Patent Publication Number: US-2022229282-A1

Title: Light irradiation device and light irradiation system

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application is a Bypass Continuation of International Application No. PCT/JP2020/030964, filed on Aug. 17, 2020, which claims priority to Japanese Patent Application No. 2019-190447, filed on Oct. 17, 2019. The contents of these applications are incorporated herein by reference in their entirety. 
    
    
     TECHNICAL FIELD 
     The disclosed embodiments relate to a light irradiation device and a light irradiation system. 
     BACKGROUND ART 
     In cancer treatment, surgical, radiological, and pharmacological (chemical) methods are used alone or in combination, and development of each of these techniques is progressing in recent years. However, there are many cancers for which a satisfactory treatment technique has not yet been found, and further development of the treatment techniques is expected. A method called photodynamic therapy (PDT) is known as one of these cancer treatment techniques. In PDT, a photosensitizer is administered intravenously and then irradiated with light, to generate reactive oxygen in cancer cells and kill the cancer cells (see, for example, Non-Patent Literature 1). However, in PDT, the photosensitizer is accumulated with low selectivity in the cancer cells, so that the magnitude of the side effects caused by the uptake of the photosensitizer into normal cells is an issue and thus, PDT is not widely used as a treatment technique. 
     Therefore, a treatment technique that is attracting attention in recent years is near-infrared photoimmunotherapy (NIR-PIT). NIR-PIT uses a conjugate in which two compounds, an antibody against a specific antigen of cancer cells and a photosensitizer (for example, IRDye 700DX), are bound. When administered intravenously, this conjugate selectively accumulates in cancer cells in the body. Subsequently, if irradiation with light having an excitation wavelength (for example, 690 nm) of the photosensitizer in the conjugate is performed, the conjugate is activated and exhibits an anticancer effect (see, for example, Patent Literature 1). Selective accumulation of antibodies in the cancer and local light irradiation in NIR-PIT allow for reduction of side effects compared to PDT. Further, in NIR-PIT, irradiation with light in the near-infrared region of 690 nm (NIR irradiation) is performed, for example, and thus, an effect of the NIR irradiation on the immune system can also be expected (see, for example, Non-Patent Literature 2). 
     A certain wavelength region including the 690 nm region of the example described above is also called a spectroscopic window of a living body. Although light in this wavelength region is absorbed less by biological components than light in other wavelength regions, the light does not sufficiently penetrate when light irradiation is performed from the body surface, and thus, there is a problem in that NIR-PIT cannot be applied to cancers deep inside the body. Therefore, in recent years, research is being conducted on NIR-PIT in which light irradiation is performed at a position closer to the cancer cells, instead of light irradiation from the body surface (see, for example, Non-Patent Literature 3). For example, Patent Literature 2 to Patent Literature 4 disclose devices that can be used in such PDT and NIR-PIT. All of the devices described in Patent Literature 2 to Patent Literature 4 are inserted into a living body lumen such as blood vessel to be used, so that the deep inside of the body can be irradiated with a light transmitted by an optical fiber. Also, in the device described in Patent Literature 5, a wound is caused with a laser light in body tissues. 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: JP 2014-523907 W 
     Patent Literature 2: JP 2018-000867 A 
     Patent Literature 3: JP 2007-528752 W 
     Patent Literature 4: JP 2001-037892 A 
     Patent Literature 5: JP 2009-533078 W 
     Non-Patent Literature 
     Non-Patent Literature 1: Makoto Mitsunaga, Mikako Ogawa, Nobuyuki Kosaka Lauren T. Rosenblum, Peter L. Choyke, and Hisataka Kobayashi, Cancer Cell-Selective In Vivo Near Infrared Photoimmunotherapy Targeting Specific Membrane Molecules, Nature Medicine 2012 17(12): p. 1685-1691 
     Non-Patent Literature 2: Kazuhide Sato, Noriko Sato, Biying Xu, Yuko Nakamura, Tadanobu Nagaya, Peter L. Choyke, Yoshinori Hasegawa, and Hisataka Kobayashi, Spatially selective depletion of tumor-associated regulatory T cells with near-infrared photoimmunotherapy, Science Translational Medicine 2016 Vol. 8 Issue 352, ra110 
     Non-Patent Literature 3: Shuhei Okuyama, Tadanobu Nagaya, Kazuhide Sato, Fusa Ogata, Yasuhiro Maruoka, Peter L. Choyke, and Hisataka Kobayashi, Interstitial near-infrared photoimmunotherapy: effective treatment areas and light doses needed for use with fiber optic diffusers, Oncotarget 2018 Feb. 16; 9(13): p. 11159-11169 
     SUMMARY 
     Technical Problem 
     Herein, an optical fiber generally transmits light by total light reflection using a difference in refractive index between a core and a clad covering an outer peripheral surface of the core, and emits light from the core exposed on a distal end of the optical fiber. On the other hand, in a device that is used so as to be inserted into a living body lumen to irradiate a deep inside of the body with light, a direction of the light irradiation is preferably a direction of tissues surrounding the living body lumen, i.e. a direction intersecting with a long axial direction of the device. In this regard, the devices described in Patent Literature 4 and Patent Literature 5 include a guide means (guide member), and the optical fiber is moved using the guide means, so that the distal end of the optical fiber can be oriented in a direction intersecting with the long axial direction of the device. However, the techniques described in Patent Literature 4 and Patent Literature 5 have had a problem that the device has a complicated structure and an increased diameter. In addition, for the devices described in Patent Literature 2 and Patent Literature 3, the light irradiation in the direction intersecting with the long axial direction of the device is not taken into consideration. 
     It is noted that this problem is not limited to PDT and NIR-PIT, and is common to all devices used in examinations or treatments including a light irradiation process in the body. Further, such a problem is not limited to devices to be inserted into a blood vessel, and is common to all devices to be inserted into living body lumens, such as a vascular system, a lymphatic system, a biliary system, a urinary system, a respiratory system, a digestive system, a secretory gland, and a reproductive organ. 
     The disclosed embodiments have been contrived to solve at least a part of the above-mentioned problems, and an object of the disclosed embodiments is to decrease a diameter of a device that can emit light from an optical fiber in a direction intersecting with a long axial direction of the device. 
     Solution to Problem 
     The disclosed embodiments have been made to solve at least a part of the above-described problems, and can be implemented as the following aspects. 
     (1) According to one aspect of the disclosed embodiments, a light irradiation device having an elongated outer shape is provided. The light irradiation device includes: an optical fiber that emits a light from its distal end and includes a curved part, in which the curved part orients the distal end in a direction intersecting with a long axial direction of the light irradiation device; a light transmitting holding member that retains a shape of the curved part of the optical fiber. The optical fiber includes a core, or the optical fiber includes the core and one or more covering layers, and the holding member has a refractive index lower than of a member constituting an outer surface of the optical fiber. 
     According to this configuration, while the distal end of the optical fiber is oriented in the direction intersecting the long axial direction of the light irradiation device by the curved part, the shape of the curved part is retained by the holding member. Thereby, movement of the optical fiber by using a guide means simplifies the configuration of the light irradiation device compared to a configuration in which the distal end of the optical fiber is oriented in a direction intersecting with the long axial direction of the light irradiation device, so that the diameter of the light irradiation device can be decreased. In addition, the holding member has a refractive index lower than of the member constituting the outer surface of the optical fiber. Thus, the light inside the optical fiber can be reflected at a boundary between the member constituting the outer surface of the optical fiber and the holding member e.g. compared to a case where the shape of the curved part is retained using a holding member having a refractive index equivalent to or higher than that of the member constituting the outer surface of the optical fiber. As a result, the light irradiation device having this configuration makes it possible to reduce light leakage from the inside of the optical fiber. 
     (2) In the light irradiation device according to the aspect described above, the holding member may be arranged at least adjacent to an inner peripheral side of the curved part. 
     According to this configuration, the shape of the curved part of the optical fiber can be retained at least from the inner peripheral side of the curved part. The inner peripheral side of the curved part is, in other words, a direction in which the distal end of the optical fiber is oriented, i.e. a direction in which the light is emitted from the optical fiber. Herein, in general, the material for forming the holding member has a refractive index higher than of air. Thus, for example, the light leakage in the direction not for the light emission from the optical fiber can be further reduced, by leaving a void on the outer peripheral side (direction in which the light is not emitted from the optical fiber) of the curved part without disposing the holding member. 
     (3) In the light irradiation device according to the aspects described above, the holding member includes an inner holding member arranged adjacent to the inner peripheral side of the curved part and an outer holding member arranged adjacent to the outer peripheral side of the curved part, and the outer holding member may have a refractive index lower than of the inner holding member. 
     According to this configuration, the shape of the curved part can be firmly retained from different directions of the inner peripheral side and the outer peripheral side of the curved part. The outer holding member disposed on the outer peripheral side of the curved part has a refractive index lower than of the inner holding member disposed on the inner peripheral side of the curved part. Thus, the light leakage from the outer holding member arranged in the direction not for the light emission from the optical fiber can be more reduced compared to the light leakage from the inner holding member arranged in the direction of the light emission from the optical fiber. 
     (4) In the light irradiation device according to the aspects described above, the inner holding member includes a first inner holding member disposed on the distal end side and a second inner holding member disposed on the proximal end side, and the second inner holding member may have a refractive index lower than of the first inner holding member and higher than of the outer holding member. 
     According to this configuration, since the inner holding member includes the first inner holding member disposed on the distal end side and the second inner holding member disposed on the proximal end side, a degree of the light leakage can be changed by controlling the refractive indices of the first and second inner holding members. The second inner holding member has a refractive index lower than of the first inner holding member and higher than of the outer holding member. Thus, the light leakage from the outer holding member arranged in the direction not for the light emission from the optical fiber can be more reduced compared to the light leakage from the first and second inner holding members arranged in the direction of the light emission from the optical fiber. Furthermore, the light leakage from the second inner holding member disposed on the proximal end side can be more reduced compared to the light leakage from the first inner holding member disposed on the distal end side. 
     (5) The light irradiation device according to the aspects described above further includes a hollow shaft accommodating the optical fiber and the holding member, wherein the proximal end side with respect to the holding member within the hollow shaft may be filled with a resin member having a refractive index lower than of the holding member. 
     According to this configuration, since the proximal end side with respect to the holding member within the hollow shaft is filled with the resin member, the elongated shape of the light irradiation device can be maintained. In addition, since the resin member has the refractive index lower than of the holding member, the light leakage can be reduced via the resin member. 
     (6) In the light irradiation device according to the aspects described above, a part on the distal end side of the curved part protrudes from the distal end of the hollow shaft, and the holding member may cover the periphery of the curved part protruding from the hollow shaft. 
     According to this configuration, a part on the distal end side of the curved part, i.e. the distal end of the optical fiber is protruded from the distal end of the hollow shaft, so that the light emitted from the distal end of the optical fiber can be prevented from being blocked by the hollow shaft. In addition, since the holding member covers the periphery of the protruding curved part, the periphery of the protruding curved part can be protected. 
     (7) The light irradiation device according to the aspects described above further includes the hollow shaft accommodating the optical fiber and the holding member, wherein a part on the distal end side of the curved part protrudes from the distal end of the hollow shaft, and the holding member may cover the periphery of the curved part protruding from the hollow shaft and have substantially the same outer diameter as of the hollow shaft so as to be joined to the distal end of the hollow shaft. 
     According to this configuration, a part on the distal end side of the curved part, i.e. the distal end of the optical fiber is protruded from the distal end of the hollow shaft, so that the light emitted from the distal end of the optical fiber can be prevented from being blocked by the hollow shaft. In addition, since the holding member covers the periphery of the protruding curved part, the periphery of the protruding curved part can be protected. 
     (8) According to an aspect of the disclosed embodiments, a light irradiation system is provided. This light irradiation system includes the light irradiation device according to the aspects described above, an elongated tubular catheter into which the light irradiation device is inserted, wherein the catheter has a light transmitting portion for transmitting the inside light to the outside, at a position corresponding to the distal end of the optical fiber in inserting the light irradiation device into the catheter. 
     According to this configuration, the light irradiation system includes separately the light irradiation device, and the catheter having a light transmitting portion for transmitting the inside light to the outside, at a position corresponding to the distal end of the optical fiber, and therefore the degree of freedom in designing the device can be improved and the range of procedures can be expanded. 
     It is noted that the disclosed embodiments can be realized in various aspects, for example, the disclosed embodiments can be realized in aspects such as a catheter, a light irradiation device, a light irradiation system in which the catheter and the light irradiation device are provided separately or integrally, and a manufacturing method of the catheter, the light irradiation device, and the light irradiation system. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is an explanatory diagram illustrating a configuration of a light irradiation system according to the first embodiment. 
         FIG. 2  is an explanatory diagram illustrating a cross-sectional configuration taken along line A-A of  FIG. 1 . 
         FIG. 3  is a top view of a light irradiation device viewed from direction B in  FIG. 1 . 
         FIG. 4  is an explanatory diagram illustrating a usage state of the light irradiation system. 
         FIG. 5  is an explanatory diagram illustrating a configuration of a light irradiation device according to the second embodiment. 
         FIG. 6  is an explanatory diagram illustrating a cross-sectional configuration taken along line C-C of  FIG. 5 . 
         FIG. 7  is an explanatory diagram illustrating a configuration of a light irradiation device according to the third embodiment. 
         FIG. 8  is an explanatory diagram illustrating a cross-sectional configuration taken along line D-D of  FIG. 7 . 
         FIG. 9  is an explanatory diagram illustrating a configuration of a light irradiation device according to the fourth embodiment. 
         FIG. 10  is an explanatory diagram illustrating a cross-sectional configuration taken along line E-E of  FIG. 9 . 
         FIG. 11  is an explanatory diagram illustrating a configuration of a light irradiation device according to the fifth embodiment. 
         FIG. 12  is an explanatory diagram illustrating a configuration of a light irradiation device according to the sixth embodiment. 
         FIG. 13  is an explanatory diagram illustrating a configuration of a light irradiation device according to the seventh embodiment. 
         FIG. 14  is an explanatory diagram illustrating a configuration of a light irradiation device according to the eighth embodiment. 
         FIG. 15  is an explanatory diagram illustrating a configuration of a light irradiation device according to the ninth embodiment. 
         FIG. 16  is an explanatory diagram illustrating a configuration of a light irradiation device according to the tenth embodiment. 
         FIG. 17  is an explanatory diagram illustrating a configuration of a light irradiation system according to the eleventh embodiment. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     First Embodiment 
       FIG. 1  is an explanatory diagram illustrating a configuration of a light irradiation system according to the first embodiment. The light irradiation system is inserted into a living body lumen such as a vascular system, a lymphatic system, a biliary system, a urinary system, a respiratory system, a digestive system, a secretory gland, and a reproductive organ to be used. The light irradiation system emits a light transmitted through an optical fiber, from the living body lumen toward living tissues. The light irradiation system can be used in photodynamic therapy (PDT) and near-infrared photoimmunotherapy (NIR-PIT), for example. The light irradiation system includes a catheter  1  and a light irradiation device  2  that is inserted into the catheter  1  to be used. In  FIG. 1 , the catheter  1  and the light irradiation device  2  are illustrated separately. 
     In  FIG. 1 , an axis passing through a center of the catheter  1  and an axis passing through a center of the light irradiation device  2  are represented by an axis O (dash-dot-dash line). Hereinafter, in a state where the light irradiation device  2  is inserted into the catheter  1 , it is assumed that axes passing through the centers of the light irradiation device  2  and the catheter  1  coincide with the axis O, but the axes passing through the centers of the light irradiation device  2  and the catheter  1  when the light irradiation device  2  is inserted into the catheter  1  may be different from each other. Further, in  FIG. 1 , an X-axis, a Y-axis, and a Z-axis that are orthogonal to each other are illustrated. The X-axis corresponds to a long axial direction (axis O direction) of the catheter  1  and the light irradiation device  2 , the Y-axis corresponds to a height direction of the catheter  1  and the light irradiation device  2 , and the Z-axis corresponds to a width direction of the catheter  1  and the light irradiation device  2 . Hereinafter, the left side (a −X-axis direction) in  FIG. 1  is referred to as a “distal end side” of the catheter  1 , the light irradiation device  2 , and each constitution component, and the right side (a +X-axis direction) in  FIG. 1  is referred to as a “proximal end side” of the catheter  1 , the light irradiation device  2 , and each constitution component. End portions of the catheter  1 , the light irradiation device  2 , and each constitution component located on the distal end side are referred to as a “distal end”, and the distal end and a vicinity thereof are referred to as a “distal end portion”. In addition, an end portion located on the proximal end side is referred to as a “proximal end”, and the proximal end and the vicinity thereof are referred to as a “proximal end portion”. The distal end side corresponds to a “distal side” inserted into a living body, and the proximal end side corresponds to a “proximal side” operated by an operator such as a doctor. These features are common to each drawing after  FIG. 1  illustrating an overall configuration. 
     The catheter  1  has an elongated tube shape and includes a shaft  110 , a distal tip  120 , and a connector  140 . The shaft  110  is an elongated member extending along the axis O. The shaft  110  has a substantially hollow cylindrical (tubular) shape and both ends of the shaft  110 , i.e., a distal end portion  110   d  and a proximal end portion  110   p,  are open. The shaft  110  includes a lumen  110 L inside the shaft  110 . The lumen  110 L functions as a guide wire lumen for inserting a guide wire through the catheter  1  during delivery of the catheter  1 . The lumen  110 L functions as a device lumen for inserting the light irradiation device  2  into the catheter  1  after the delivery of the catheter  1 . Using a single lumen as both the guide wire lumen and the device lumen, as described above, makes it possible to reduce the diameter of the catheter  1 . The shaft  110  may have any outer diameter, inner diameter, and length. 
     The distal tip  120  is a member that is joined to the distal end portion of the shaft  110  and advances in a living body lumen ahead of other members. As illustrated in  FIG. 1 , to facilitate the progress of the catheter  1  in the living body lumen, the distal tip  120  has an outer shape with a diameter that decreases from the proximal end side to the distal end side. A through-hole  120   h  penetrating the distal tip  120  in a direction of the axis O is formed in a substantially central part of the distal tip  120 . Here, an opening diameter Φ 1  of the through-hole  120   h  is smaller than an inner diameter Φ 2  of the lumen  110 L of the shaft  110 . Therefore, as illustrated in  FIG. 1 , at a boundary between the shaft  110  and the distal tip  120 , an inner surface  120   i  of the distal tip  120  protrudes and forms a step. An opening  120   o  of the distal tip  120  leads to the through-hole  120   h  and is used when inserting a guide wire (not illustrated) into the catheter  1 . The distal tip  120  may have any outer diameter and length. 
     The connector  140  is a member arranged on the proximal end side of the catheter  1  and gripped by the operator. The connector  140  includes a connection portion  141  having a substantially cylindrical shape and a pair of blades  142 . A distal end portion of the connection portion  141  is joined to the proximal end portion  110   p  of the shaft  110 , and a proximal end portion of the connection portion  141  is joined to the blades  142 . The blades  142  may have a structure that is integrally formed with the connector  140 . An opening  140   o  of the connector  140  leads to the lumen  110 L via the inside of the connector  140 , and is used when inserting the light irradiation device  2  into the catheter  1 . The connection portion  141  may have any outer diameter, inner diameter, and length, and the blades  142  may have any shape. 
     The shaft  110  of the catheter  1  is further provided with a light transmitting portion  139  and first marker portions  131  and  132 . The light transmitting portion  139  transmits light inside the shaft  110  to the outside. The light transmitting portion  139  is a hollow member having a substantially cylindrical shape, an outer diameter that is substantially the same as the outer diameter of the shaft  110 , and an inner diameter that is substantially the same as the inner diameter Φ 2  of the lumen  110 L of the shaft  110 . In other words, the light transmitting portion  139  is provided wholly in the circumferential direction, and wholly transmits light inside the shaft  110  to the outside in the circumferential direction. The light transmitting portion  139  is joined to the shaft  110  at each of the proximal end side and the distal end side. The light transmitting portion  139  can be formed of a transparent resin material having light-transmitting properties, such as an acrylic resin, polyethylene terephthalate, and polyvinyl chloride. 
     The first marker portions  131  and  132  function as marks indicating positions of the light transmitting portion  139 . The first marker portion  131  is provided close to the distal end portion of the light transmitting portion  139 , and functions as a mark indicating a position of the distal end portion of the light transmitting portion  139 . The first marker portion  132  is provided close to the proximal end portion of the light transmitting portion  139 , and functions as a mark indicating a position of the proximal end portion of the light transmitting portion  139 . The first marker portions  131  and  132  are hollow members each having a substantially cylindrical shape. In the example of  FIG. 1 , the first marker portions  131  and  132  are respectively arranged in recess portions formed in an outer surface of the shaft  110  and are joined to the outer surface of the shaft  110 . In other words, the first marker portions  131  and  132  are each embedded in the outer surface of the shaft  110  to surround the shaft  110  in the circumferential direction. It is noted that the first marker portions  131  and  132  may be joined to the outer surface of the shaft  110  without the recess portions, and may protrude from the outer surface of the shaft  110 . At least one of the first marker portions  131  and  132  may be omitted. 
     The light irradiation device  2  has an elongated outer shape and includes a shaft  210 , a distal tip  220 , a connector  240 , an optical fiber  250 , and a holding member  260 . The shaft  210  is an elongated member extending along the axis O. The shaft  210  has a hollow and substantially cylindrical (tubular) shape with both end portions, a distal end portion  210   d  and a proximal end portion  210   p  being opened. An opening for exposing the distal end of the optical fiber  250  is formed on the outer peripheral surface on the distal end side of the shaft  210  (described later in  FIG. 3 ). The optical fiber  250  and the holding member  260  are accommodated in (inside) the shaft  210 . A void portion inside the shaft  210  excluding the optical fiber  250  and the holding member  260  is filled with a resin member  270 . Note that the shaft  210  corresponds to the “hollow shaft”. 
     The distal tip  220  is a member that is joined to the distal end portion  210   d  of the shaft  210  and advances ahead of other members in the lumen  110 L of the catheter  1 . As illustrated in  FIG. 1 , the distal tip  220  is an almost columnar member extending in the long axis direction of the light irradiation device  2 . Here, it is preferable that an outer diameter Φ 3  of the distal tip  220  and the shaft  210  (in other words, outer diameter Φ 3  of the light irradiation device  2 ) is larger than the opening diameter Φ 1  of the through-hole  120   h  of the catheter  1  and smaller than an inner diameter Φ 2  of the shaft  110  and the light transmitting portion  139  of the catheter  1  (Φ 1 &lt;Φ 3 &lt;Φ 2 ). 
     The connector  240  is a member arranged on the proximal end side of the light irradiation device  2  and gripped by the operator. The connector  240  includes a connection portion  241  having a substantially cylindrical shape and a pair of blades  242 . A distal end portion of the connection portion  241  is joined to the proximal end portion  210   p  of the shaft  210 , and a proximal end portion of the connection portion  241  is joined to the blades  242 . The blades  242  may have a structure that is integrally formed with the connector  240 . 
       FIG. 2  is an explanatory diagram illustrating a cross-sectional configuration taken along line A-A in  FIG. 1 . The X-axis, Y-axis, and Z-axis illustrated in  FIG. 2  correspond to the X-axis, Y-axis, and Z-axis respectively in  FIG. 1 . As illustrated in the figure, the optical fiber  250  includes a core  250   c  extending in the long axial direction (axis O direction) of the light irradiation device  2 , and a clad  250   cl  that covers an outer peripheral surface (outer surface) of the core  250   c.  The core  250   c  is disposed substantially in the center of the clad  250   cl  and has a higher optical refractive index than of the clad  250   cl.  The clad  250   cl  has a uniform refractive index. The optical fiber  250  transmits the light by total light reflection using a difference in refractive index between the core  250   c  and the clad  250   cl.  In this optical fiber  250 , the clad  250   cl  corresponds to a “covering layer” that covers the core  250   c  and corresponds to a “member constituting the outer surface of the optical fiber  250 ”. 
     The optical fiber  250  according to the first embodiment is a plastic optical fiber in which the core  250   c  and the clad  250   cl  are both made of a resin. The core  250   c  can be made of e.g. a polymethylmetacrylate (PMMA), a polystyrene, a polycarbonate, a deuterated polymer, a fluorine-based polymer, a silicon-based polymer, a norbornene-based polymer, or the like. The core  250   c  is classified into a single-mode and a multi-mode depending on the number of modes for propagating the light, but either the single-mode or the multi-mode may be used in the first embodiment. Additionally, in the case of the multi-mode core  250   c,  the core  250   c  is classified into a step index and a graded index depending on a refractive index distribution, but either the step index or the graded index may be used in the first embodiment. The clad  250   cl  can be made of e.g. a fluorine-based polymer. For the optical fiber  250 , a quartz glass optical fiber or a multi-component glass optical fiber may be employed instead of the plastic optical fiber. A longitudinal length of the optical fiber  250  can be arbitrarily determined. 
     As illustrated in  FIG. 1 , the distal end side of the optical fiber  250  is inserted inside the shaft  210  and fixed by the resin member  270 . The proximal end side of the optical fiber  250  passes through the inside of the connector  240  and is pulled out to the outside. The proximal end portion of the optical fiber  250  is connected to a light source  3  via a connector not illustrated, directly, or indirectly via another optical fiber. The light source  3  is e.g. a laser light generator that generates a laser light at any wavelength. 
       FIG. 3  is a top view of the light irradiation device  2  viewed from direction B in  FIG. 1 . As illustrated in  FIG. 1 , a curved part  251  where the optical fiber  250  is curved in the +Y-axis direction is formed on the distal end portion of the optical fiber  250 . As illustrated in  FIG. 3 , the distal end (distal end surface) of the optical fiber  250  is arranged so as to be exposed on the outer peripheral surface (outer surface) of the shaft  210 . On the distal end of the optical fiber  250 , the clad  250   cl  is removed and the core  250   c  is exposed. A laser light LT generated by the light source  3  and transmitted through the optical fiber  250  is emitted from the exposed core  250   c.  That means, the core  250   c  exposed on the distal end of the optical fiber  250  functionally serves as a light irradiation portion  239  that emits the light LT to the outside. Thus, in the configuration of the first embodiment, the distal end of the optical fiber  250  that emits the laser light LT is oriented in a direction intersecting with the long axial direction (axis O direction) of the light irradiation device  2 , by the curved part  251  of the optical fiber  250 . Thereby, the light LT is emitted from the core  250   c  (light irradiation portion  239 ) exposed on the distal end of the optical fiber  250  toward one direction of the side surface of the light irradiation device  2 . 
     On the distal end (distal end surface) of the optical fiber  250 , the core  250   c  may be subjected to a well-known process (e.g. a process of diagonally cutting a distal end surface, a process of forming a notch, a sandblast process, and a chemical process). A resin body or a light reflecting mirror for transmitting, refracting, or amplifying the laser light LT may be disposed on or near the distal end of the core  250   c.  The resin body can be formed, for example, by applying an acrylic ultraviolet-curable resin containing dispersed fine quartz powder, and curing the resin using ultraviolet light. 
     The holding member  260  is a member for retaining a shape (curved shape) of the curved part  251  of the optical fiber  250 . The holding member  260  is disposed inside the shaft  210  and at a position of the curved part  251  of the optical fiber  250  ( FIG. 1 ). The holding member  260  is arranged so as to cover the entire outer peripheral surface of the curved part  251  of the optical fiber  250  ( FIG. 2 ). The holding member  260  is made of a light transmissive resin. Here, light transmissive resin means a resin that is transparent or translucent and has a property of transmitting light. As the light transmissive resin, for example, any resin such as an epoxy resin filled with an inorganic powder can be used. In the light transmissive resin used for the holding member  260 , a light transmissivity in a wavelength range used in PDT or NIR-PIT (e.g. 650 nm to 700 nm) is preferably higher than the light transmissivity in another wavelength range. The holding member  260  may be formed by mixing plural different types of light transmissive resins. 
     This light transmitting holding member  260  has a refractive index  6 R lower than a refractive index R 5  of the member constituting the outer surface of the optical fiber  250  (i.e. clad  250   cl ) (R 6 &lt;R 5 ). In addition, the resin member  270  has a refractive index R 7  lower than the refractive index R 6  of the holding member  260  (R 7 &lt;R 6 ). That means, the relationship between the refractive index R 5  of the clad  250   cl,  the refractive index R 6  of the holding member  260 , and the refractive index R 7  of the resin member  270  is represented by “R 7 &lt;R 6 &lt;R 5 ”. Representative values such as catalogue values can be used for the refractive index R 5  of the clad  250   cl,  the refractive index R 6  of the holding member  260 , and the refractive index R 7  of the resin member  270 . 
     Here, it is assumed that a first member and a second member having different refractive indices are arranged adjacent to each other. In this case, generally, the greater a difference in refractive index between the first member and the second member is, the more likely it is that a light advancing from the first member to the second member is totally reflected at a boundary surface between the first and second members (i.e. the light does not advance to the second member). On the other hand, the smaller the difference in refractive index between the first member and the second member, the more likely it is that the light advances from the first member to the second member while being refracted at the boundary surface between the first and second members. In this regard, in the light irradiation device  2  according to the first embodiment, the refractive index R 6  of the holding member  260  is lower than the refractive index R 5  of the clad  250   cl  constituting the outer surface of the optical fiber  250  (R 6 &lt;R 5 ). Thereby, for example, the light inside the optical fiber  250  can be reflected at a boundary between the clad  250   cl  and the holding member  260 , compared to the case where the shape of the curved part  251  is retained using the holding member having a refractive index equivalent to or higher than the refractive index of the clad  250   cl.  Thus, the light leakage can be reduced via the holding member  260 . In addition, the resin member  270  has a refractive index R 7  lower than the refractive index R 6  of the holding member  260  (R 7 &lt;R 6 ). For this reason, when comparing the resin member  270  with the holding member  260 , the difference in refractive index between the resin member  270  and the clad  250   cl  is larger than the difference in refractive index between the holding member  260  and the clad  250   cl.  Consequently, the light leakage can be reduced via the resin member  270 . 
     The optical fiber  250  consists only of the core  250   c  and need not have any covering layer such as the clad  250   cl.  In this case, the core  250   c  corresponds to the “member constituting the outer surface of the optical fiber  250 ”. At this time, the refractive index R 6  of the holding member  260  is lower than a refractive index R 51  of the core  250   c  (R 6 &lt;R 51 ). The optical fiber  250  may further include a cover for covering the outer peripheral surface of the clad  250   cl.  In this case, the clad  250   cl  and the cover correspond to the “covering layer” for covering the core  250   c,  and the cover corresponds to the “member constituting the outer surface of the optical fiber  250 ”. At this time, the refractive index R 6  of the holding member  260  is lower than a refractive index R 52  of the cover (R 6 &lt;R 52 ). Furthermore, when the cover is composed of a plurality of layers, the outermost cover corresponds to the “member constituting the outer surface of the optical fiber  250 ”. At this time, the refractive index R 6  of the holding member  260  is lower than a refractive index R 53  of the outermost cover (R 6 &lt;R 53 ). 
       FIG. 1  will be explained again. Second marker portions  231  and  232  are further disposed on the shaft  210  of the light irradiation device  2 . The second marker portions  231  and  232  function as marks indicating positions of the light irradiation portion  239  (i.e. the distal end of the optical fiber  250 ). As illustrated in  FIG. 3 , the second marker portion  231  is provided close to the distal end side of the light irradiation portion  239 , and functions as a mark indicating a position of the distal end side of the light irradiation portion  239 . The second marker portion  232  is provided close to the proximal end side of the light irradiation portion  239 , and functions as a mark indicating a position of the proximal end side of the light irradiation portion  239 . The second marker portions  231  and  232  are hollow members each having a substantially cylindrical shape. In the example of  FIG. 1 , the second marker portions  231  and  232  are respectively arranged in recess portions formed in the outer surface of the shaft  210  and are joined to the outer surface of the shaft  210 . In other words, the second marker portions  231  and  232  are each embedded in the outer surface of the shaft  210  to surround the shaft  210  in a circumferential direction. It is noted that the second marker portions  231  and  232  may be joined to the outer surface of the shaft  210  without the recess portions, and may protrude from the outer surface of the shaft  210 . At least one of the second marker portions  231  and  232  may be omitted. 
     The first marker portions  131  and  132  of the catheter  1  and the second marker portions  231  and  232  of the light irradiation device  2  can be formed of a radiopaque resin material or a radiopaque metal material. For example, when a resin material is used, the first marker portions  131  and  132  and the second marker portions  231  and  232  can be formed by using a mixture of a radiopaque material, such as bismuth trioxide, tungsten, or barium sulfate, and a resin material, such as a polyamide resin, a polyolefin resin, a polyester resin, a polyurethane resin, a silicon resin, or a fluororesin. When a metal material is used, for example, the first marker portions  131  and  132  and the second marker portions  231  and  232  can be formed of a radiopaque material such as gold, platinum, tungsten, or an alloy containing these elements (for example, a platinum-nickel alloy). 
     The shaft  110  of the catheter  1 , the shaft  210  of the light irradiation device  2 , and the resin member  270  of the light irradiation device  2  are preferably antithrombotic, flexible, and biocompatible, and can be formed of a resin material or a metal material. For example, a polyamide resin, a polyolefin resin, a polyester resin, a polyurethane resin, a silicon resin, a fluororesin, and the like can be employed as the resin material. For example, stainless steel such as SUS304, a nickel-titanium alloy, a cobalt-chromium alloy, tungsten steel and the like can be employed as the metal material. Further, the shaft  110  and the shaft  210  can be formed as a bonded structure in which a plurality of the above-mentioned materials are combined. The distal tip  120  of the catheter  1  and the distal tip  220  of the light irradiation device  2  are preferably flexible, and can be formed of, for example, a resin material such as polyurethane and a polyurethane elastomer. The connector  140  of the catheter  1  and the connector  240  of the light irradiation device  2  can be formed of a resin material such as a polyamide, a polypropylene, a polycarbonate, a polyacetal, and a polyether sulfone. 
       FIG. 4  is an explanatory diagram illustrating a usage state of the light irradiation system. A method of using the light irradiation system will be described with reference to  FIGS. 1 and 4 . First, an operator inserts a guide wire into a living body lumen. Next, the operator inserts a proximal end side of the guide wire from the opening  120   o  of the distal tip  120  of the catheter  1  illustrated in  FIG. 1 , through the lumen  110 L so that the guide wire protrudes from the opening  140   o  of the connector  140 . Subsequently, the operator pushes the catheter  1  into the living body lumen along the guide wire, and the light transmitting portion  139  of the catheter  1  is delivered to a target site for light irradiation (for example, in the case of NIR -PIT, a vicinity of a cancer cell). Thus, by inserting the guide wire from the through-hole  120   h  formed in the distal tip  120  of the catheter  1 , the operator can easily deliver the catheter  1  to the target site in the living body lumen. It is noted that, during delivery, the operator can position the catheter  1  in the living body lumen, while observing, in an X-ray image, the positions of the first marker portions  131  and  132  arranged in the vicinity of the light transmitting portion  139 . Afterwards, the surgeon removes the guide wire from the catheter  1 . 
     Next, the operator inserts the light irradiation device  2  from the opening  140   o  of the connector  140  of the catheter  1 . The operator pushes the light irradiation device  2  toward the distal end side of the catheter  1 , along the lumen  110 L of the catheter  1 . Here, as described above, if the outer diameter Φ 3  of the light irradiation device  2  is smaller than the diameter Φ 2  of the lumen  110 L of the catheter  1  and larger than the diameter Φ 1  of the through-hole  120   h  of the distal tip  120 , a distal end surface  220 e of the light irradiation device  2  abuts against the inner surface  120   i  of the distal tip  120  when the light irradiation device  2  is inserted into the catheter  1 , and thus, it is possible to prevent the light irradiation device  2  from being advanced beyond the distal end of the catheter  1  ( FIG. 4 ). 
     After that, the operator aligns the light irradiation portion  239  (distal end of the optical fiber  250 ) with the light transmitting portion  139  in the direction of the axis O (X-axis direction), while observing, in an X-ray image, a positional relationship between the first marker portions  131  and  132  and the second marker portions  231  and  232 . Thus, the laser light LT emitted from the light irradiation portion  239  (distal end of the optical fiber  250 ) can be transmitted through the light transmitting portion  139  of the catheter  1  and emitted to a living tissue on the outside. It is noted that, in the catheter  1  according to the first embodiment, the light transmitting portion  139  is provided in the entire circumferential direction. Therefore, in the light irradiation system according to the first embodiment, the operator only needs to achieve alignment between the light transmitting portion  139  and the light irradiation portion  239  in the direction of the axis O (X-axis direction), and does not need to achieve alignment between the light transmitting portion  139  and the light irradiation portion  239  in the circumferential direction. 
     As explained above, in the light irradiation device  2  according to the first embodiment, while the distal end of the optical fiber  250  is oriented in a direction intersecting with the long axial direction (axis O direction) of the light irradiation device  2  by the curved part  251 , the shape of the curved part  251  is retained by the holding member  260  ( FIG. 4 ). Thereby, for example, movement of the optical fiber by using a guide means simplifies the configuration of the light irradiation device  2  compared to a configuration in which the distal end of the optical fiber is oriented in a direction intersecting with the long axial direction of the light irradiation device, so that the diameter of the light irradiation device  2  can be decreased. In addition, the refractive index R 6  of the holding member  260  is lower than the refractive index R 5  of the clad  250   cl  (member constituting the outer surface of the optical fiber  250 ). Thereby, as explained in  FIG. 2 , for example, the light inside the optical fiber  250  can be reflected at the boundary between the clad  250   cl  and the holding member  260 , compared to the case where the shape of the curved part  251  is retained using the holding member having a refractive index equivalent to or higher than the refractive index of the clad  250   cl.  As a result, the light irradiation device  2  according to the first embodiment makes it possible to reduce light leakage from the inside of the optical fiber  250 . 
     In the light irradiation device  2  according to the first embodiment, the proximal end side with respect to the holding member  260  within the shaft  210  (hollow shaft) is filled with the resin member  270 . Thereby, the elongated shape of the light irradiation device  2  can be easily retained. In addition, the refractive index R 7  of the resin member  270  is lower than the refractive index R 6  of the holding member  260 . Consequently, as explained in  FIG. 2 , the light leakage can be reduced via the resin member  270 . 
     Further, the light irradiation system according to the first embodiment separately includes the light irradiation device  2 , and the catheter  1  having the light transmitting portion  139  for transmitting the inside light LT to the outside, which is disposed at a position corresponding to the distal end (i.e. the light irradiation portion  239 ) of the optical fiber  250 . Consequently, the degree of freedom in designing the device can be improved and also the range of procedures can be expanded. 
     Second Embodiment 
       FIG. 5  is an explanatory diagram illustrating a configuration of a light irradiation device  2 A according to the second embodiment.  FIG. 6  is an explanatory diagram illustrating a cross-sectional configuration taken along line C-C of  FIG. 5 . Alight irradiation system according to the second embodiment includes the catheter  1  explained in the first embodiment and the light irradiation device  2 A illustrated in  FIG. 5  and  FIG. 6 . The light irradiation device  2 A includes a holding member  260 A instead of the holding member  260  and does not include the resin member  270 . The holding member  260 A is arranged adjacent to the inner peripheral side of the curved part  251  of the optical fiber  250 . The inner peripheral side of the curved part  251  means the inner side of the curved part on the outer peripheral surface of the optical fiber  250 , and means, in the examples of  FIG. 5  and  FIG. 6 , the +Y-axis direction side. The resin member  270  is disposed on the outer peripheral side ( FIG. 5  and  FIG. 6 : −Y-axis direction side) of the curved part  251  of the optical fiber  250 . A dimensional relationship in refractive index between the clad  250   cl,  the holding member  260 A, and the resin member  270  is the same as in the first embodiment. 
     In this way, the configuration of the holding member  260 A of the light irradiation device  2 A can be modified in various ways, and the holding member  260 A may be disposed only on the inner peripheral side of the curved part  251  of the optical fiber  250 . In the example of  FIG. 6 , the holding member  260 A is disposed on the inner peripheral side of the curved part  251  over a range of about 170 degrees in the circumferential direction, but the range in which the holding member  260 A is arranged can be arbitrarily changed. The angular range may be e.g. 30 degrees, 90 degrees, or 270 degrees. In the examples of  FIG. 5  and  FIG. 6 , although the outer peripheral side of the curved part  251  is filled with the resin member  270 , the outer peripheral side of the curved part  251  need not be filled with the resin member  270 , and may be e.g. a void. 
     Also, the light irradiation system according to the second embodiment as described above makes it possible to exhibit an effect similar to that in the first embodiment described above. In addition, in the light irradiation device  2 A according to the second embodiment, the shape of the curved part  251  of the optical fiber  250  can be retained from at least the inner peripheral side of the curved part  251 . The inner peripheral side of the curved part  251  is, in other words, a direction in which the distal end of the optical fiber  250  is oriented (i.e. a direction toward the light irradiation portion  239 ) and is the direction in which the light LT is emitted from the optical fiber  250 . Herein, in general, the whole of the materials constituting the holding member  260 A has a refractive index higher than of air. Thus, the light leakage in the direction not for the light emission from the optical fiber  250  can be further reduced, by leaving a void on the outer peripheral side (direction in which the light is not emitted from the optical fiber  250 ) of the curved part  251  without disposing the holding member  260 A and the resin member  270 , as in the light irradiation device  2 A according to the second embodiment. 
     Third Embodiment 
       FIG. 7  is an explanatory diagram illustrating a configuration of a light irradiation device  2 B according to the third embodiment.  FIG. 8  is an explanatory diagram illustrating a cross-sectional configuration taken along line D-D of  FIG. 7 . A light irradiation system according to the third embodiment includes the catheter  1  explained in the first embodiment and the light irradiation device  2 B illustrated in  FIG. 7  and  FIG. 8 . The light irradiation device  2 B includes a holding member  260 B instead of the holding member  260 . The holding member  260 B includes an inner holding member  261  and an outer holding member  262 . 
     The inner holding member  261  is arranged adjacent to the inner peripheral side of the curved part  251  of the optical fiber  250 . The outer holding member  262  is arranged adjacent to the outer peripheral side of the curved part  251  of the optical fiber  250 . In the example of  FIG. 8 , the inner holding member  261  is disposed on the inner peripheral side of the curved part  251  over a range of about 170 degrees in the circumferential direction, and the outer holding member  262  is disposed on the outer peripheral side of the curved part  251  over the remaining angular range (range of about 190 degrees) in the circumferential direction. However, the angular range in which the inner holding member  261  is disposed in the circumferential direction and the angular range in which the outer holding member  262  is disposed in the circumferential direction can be arbitrarily changed. 
     The inner holding member  261  and the outer holding member  262  are each made of different light transmissive resins. The outer holding member  262  has a refractive index R 62  lower than a refractive index R 61  of the inner holding member  261  (R 62 &lt;R 61 ). As in the first embodiment, the refractive indices R 61  and R 62  of the holding member  260 B (inner holding member  261  and outer holding member  262 ) are both lower than the refractive index R 5  of the clad  250   cl  constituting the outer surface of the optical fiber  250 . Thus, a dimensional relationship therebetween is represented by R 62 &lt;R 61 &lt;R 5 . 
     As described above, the configuration of the holding member  260 B of the light irradiation device  2 B can be modified in various ways, and the holding member  260 B may include the inner holding member  261  and the outer holding member  262  which are each made of different light transmissive resins. Also, the light irradiation system according to the third embodiment as described above makes it possible to exhibit an effect similar to that in the first embodiment described above. In the light irradiation device  2 B according to the third embodiment, the shape (curved shape) of the curved part  251  can be firmly retained from different directions of the inner peripheral side and the outer peripheral side of the curved part  251 . In addition, the refractive index R 62  of the outer holding member  262  disposed on the outer peripheral side (the opposite side to the light LT-emitting side, i.e. −Y-axis direction in the example of  FIG. 7 ) of the curved part  251  is lower than the refractive index R 61  of the inner holding member  261  disposed on the inner peripheral side (the light LT-emitting side, i.e. +Y-axis direction in the example of  FIG. 7 ) of the curved part  251 . For this reason, when comparing the outer holding member  262  with the inner holding member  261 , the difference in refractive index between the outer holding member  262  and the clad  250   cl  is larger than the difference in refractive index between the inner holding member  261  and the clad  250   cl.  Thus, the light leakage from the outer holding member  262  arranged in the direction not for the light emission from the optical fiber  250  can be more reduced compared to the light leakage from the inner holding member  261  arranged in the direction of the light emission from the optical fiber  250 . 
     In the light irradiation device  2 B according to the third embodiment, the dimensional relationship between the refractive index R 61  of the inner holding member  261  and the refractive index R 62  of the outer holding member  262  may be reversed (R 61 &lt;R 62 ). Also, the refractive index R 61  of the inner holding member  261  and the refractive index R 62  of the outer holding member  262  may be substantially equal. Also in this way, the same effect as in the first embodiment can be exhibited, and the shape of the curved part  251  can be firmly retained from different directions of the inner peripheral side and the outer peripheral side of the curved part  251 . 
     Fourth Embodiment 
       FIG. 9  is an explanatory diagram illustrating a configuration of a light irradiation device  2 C according to the fourth embodiment.  FIG. 10  is an explanatory diagram illustrating a cross-sectional configuration taken along line E-E of  FIG. 9 . A light irradiation system according to the fourth embodiment includes the catheter  1  explained in the first embodiment and the light irradiation device  2 C illustrated in  FIG. 9  and  FIG. 10 . The light irradiation device  2 C includes a holding member  260 C instead of the holding member  260 . The holding member  260 C includes an inner holding member  261 C and an outer holding member  262 C. 
     As illustrated in  FIG. 10 , the inner holding member  261 C is disposed on the inner peripheral side of the curved part  251  of the optical fiber  250  over a range of about 100 degrees in the circumferential direction. Similarly, the outer holding member  262 C is disposed on the outer peripheral side of the curved part  251  of the optical fiber  250  over a range of about 100 degrees in the circumferential direction. In the examples of  FIG. 10 , although a portion in the remaining angle range in the circumferential direction is filled with the resin member  270 , the portion in the remaining angle range in the circumferential direction of the curved part  251  need not be filled with the resin member  270 , and may be e.g. a void. The materials of the inner holding member  261 C and the outer holding member  262 C are the same as in the third embodiment. A dimensional relationship in refractive index between the inner holding member  261 C, the outer holding member  262 C, and the clad  250   cl  is the same as in the third embodiment (R 62 &lt;R 61 &lt;R 5 ). 
     As described above, the configuration of the holding member  260 C of the light irradiation device  2 C can be modified in various ways, and the holding member  260 C may include the inner holding member  261 C and the outer holding member  262 C, which are arranged apart from each other in the circumferential direction. Also, the light irradiation system according to the fourth embodiment as described above makes it possible to exhibit an effect similar to those in the first and third embodiments described above. 
     Fifth Embodiment 
       FIG. 11  is an explanatory diagram illustrating a configuration of a light irradiation device  2 D according to the fifth embodiment. A light irradiation system according to the fifth embodiment includes the catheter  1  explained in the first embodiment and the light irradiation device  2 D illustrated in  FIG. 11 . The light irradiation device  2 D includes a holding member  260 D instead of the holding member  260 . The holding member  260 D includes a first inner holding member  261 D, a second inner holding member  263 D, and an outer holding member  262 D. 
     The first inner holding member  261 D is disposed on the inner peripheral side of the curved part  251  of the optical fiber  250  and on the distal end side (−X-axis direction) of the light irradiation device  2 D. The second inner holding member  263 D is disposed on the inner peripheral side of the curved part  251  of the optical fiber  250  and on the proximal end side (+X-axis direction) of the light irradiation device  2 D. The first inner holding member  261 D and the second inner holding member  263 D correspond to the “inner holding members”. The outer holding member  262 D is arranged adjacent to the outer peripheral side of the curved part  251  of the optical fiber  250 . A peripheral range in which the first inner holding member  261 D, the second inner holding member  263 D, and the outer holding member  262 D are disposed can be arbitrarily determined. For example, it is allowed to adopt a configuration in which the first inner holding member  261 D and the second inner holding member  263 D are disposed in a predetermined angular range in the circumferential direction, and the outer holding member  262 D is disposed in the remaining angular range in the circumferential direction, as in the third embodiment. In addition, for example, it is allowed to adopt an arrangement in which the first inner holding member  261 D and the second inner holding member  263 D are disposed in a predetermined angular range in the circumferential direction, the outer holding member  262 D is disposed in another predetermined angular range in the circumferential direction, and the remaining angular range in the circumferential direction is filled with the resin member  270 , as in the fourth embodiment. 
     The first inner holding member  261 D, the second inner holding member  263 D, and the outer holding member  262 D are each made of different light transmissive resins. The second inner holding member  263 D has a refractive index R 63  lower than the refractive index R 61  of the first inner holding member  261 D and higher than of the outer holding member  262 D (R 62 &lt;R 63 &lt;R 61 ). As in the first embodiment, the refractive indices R 61 , R 63 , and R 62  of the holding member  260 D (first inner holding member  261 D, second inner holding member  263 D, and outer holding member  262 D) are all lower than the refractive index R 5  of the clad  250   cl  constituting the outer surface of the optical fiber  250 . Thus, a dimensional relationship therebetween is represented by R 62 &lt;R 63 &lt;R 61 &lt;R 5 . 
     As described above, the configuration of the holding member  260 D of the light irradiation device  2 D can be modified in various ways, and the inner holding member of the holding member  260 D may include the first inner holding member  261 D and the second inner holding member  263 D which are each made of different light transmissive resins. Three or more inner holding members may be disposed on the inner peripheral side of the curved part  251  of the optical fiber  250 . Also, the light irradiation system according to the fifth embodiment as described above makes it possible to exhibit an effect similar to that in the first embodiment described above. In the light irradiation device  2 D according to the fifth embodiment, since the inner holding member includes the first inner holding member  261 D disposed on the distal end side and the second inner holding member  263 D disposed on the proximal end side, a degree of the light leakage can be changed by controlling the refractive indices R 61  and R 63  of the first and second inner holding members  261 D and  263 D. The refractive index R 63  of the second inner holding member  263 D is lower than the refractive index R 61  of the first inner holding member  261 D and higher than the refractive index R 62  of the outer holding member  262 D. Thus, the light leakage from the outer holding member  262 D arranged in the direction not for the light emission from the optical fiber  250  can be more reduced compared to the light leakage from the first and second inner holding members  261 D and  263 D arranged in the direction of the light emission from the optical fiber  250 . Furthermore, the light leakage from the second inner holding member  263 D disposed on the proximal end side can be more reduced compared to the light leakage from the first inner holding member  261 D disposed on the distal end side. 
     Sixth Embodiment 
       FIG. 12  is an explanatory diagram illustrating a configuration of a light irradiation device  2 E according to the sixth embodiment. A light irradiation system according to the sixth embodiment includes the catheter  1  explained in the first embodiment and the light irradiation device  2 E illustrated in  FIG. 12 . The light irradiation device  2 E does not include the resin member  270  explained in the first embodiment, and a portion inside the shaft  210 , where the optical fiber  250  and the holding member  260  are not accommodated, is a void. As described above, the configuration of the light irradiation device  2 E can be modified in various ways, and the light irradiation device  2 E need not include the resin member  270 , and may include another reinforcing member in place of the resin member  270 . As another reinforcing member, for example, a braided body or a coil body can be employed. Such a reinforcing member may be disposed inside the shaft  210  or embedded in a thick-walled portion of the shaft  210 . Also, the light irradiation system according to the sixth embodiment as described above makes it possible to exhibit an effect similar to that in the first embodiment described above. 
     Seventh Embodiment 
       FIG. 13  is an explanatory diagram illustrating a configuration of a light irradiation device  2 F according to a seventh embodiment. A light irradiation system according to the seventh embodiment includes the catheter  1  explained in the first embodiment and the light irradiation device  2 F illustrated in  FIG. 13 . The light irradiation device  2 F does not have the distal tip  220 , and includes an optical fiber  250 F instead of an optical fiber  250 , and includes an optical fiber  250 F instead of the optical fiber  250 , and a holding member  260 F instead of the holding member  260 . 
     The optical fiber  250 F is arranged such that a part of the distal end side of the curved part  251  protrudes from the distal end of the shaft  210 . The protruding length of the curved part  251  can be arbitrarily determined. The holding member  260 F covers the periphery of the curved part  251  protruding from the shaft  210 . In other words, the holding member  260 F covers the entire surface in the circumferential direction of the curved part  251  protruding from the shaft  210 . The holding member  260 F is shaped such that the diameter gradually decreases from the proximal end side toward the distal end side and the distal end portion is rounded. Since the holding member  260 F is arranged along the curved part  251  that is curved in the +Y-axis direction, the shape of the holding member  260  with the decreasing diameter is asymmetric with respect to the axis O in the cross section illustrated in  FIG. 13 . The largest outer diameter of the holding member  260 F is equal to the outer diameter Φ 3  of the shaft  210  (in other words, the outer diameter Φ 3  of the light irradiation device  2 F. A material and a refractive index of the holding member  260 F are the same as those in the first embodiment. 
     As described above, the configuration of the light irradiation device  2 F can be modified in various ways, and the light irradiation device  2 F may be configured such that the curved part  251  of the optical fiber  250 F protrudes from the shaft  210 , and the holding member  260 F that covers the periphery of the protruding curved part  251  is further provided. At this time, the shape of the holding member  260 F can be arbitrarily changed. For example, the holding member  260 F need not cover the entire periphery of the curved part  251  protruding from the shaft  210 , and may cover at least a part of the curved part  251 . Also, the light irradiation system according to the seventh embodiment as described above makes it possible to exhibit an effect similar to that in the first embodiment described above. In the light irradiation device  2 F according to the seventh embodiment, a part on the distal end side of the curved part  251 , i.e. the distal end of the optical fiber  250 F is protruded from the distal end of the shaft  210  (hollow shaft), so that the light LT emitted from the distal end of the optical fiber  250 F can be prevented from being blocked by the shaft  210 . In addition, since the holding member  260 F covers the periphery of the protruding curved part  251 , the periphery of the protruding curved part  251  can be protected. 
     Eighth Embodiment 
       FIG. 14  is an explanatory diagram illustrating a configuration of a light irradiation device  2 G according to the eighth embodiment. Alight irradiation system according to the eighth embodiment includes the catheter  1  explained in the first embodiment and the light irradiation device  2 G illustrated in  FIG. 14 . The light irradiation device  2 G has a holding member  260 G having a shape different from that in the seventh embodiment, in the configuration in which the curved part  251  of the optical fiber  250 F explained in the seventh embodiment protrudes from the shaft  210 . The holding member  260 G covers the periphery (entire surface in the circumferential direction) of the curved part  251  protruding from the shaft  210 . The holding member  260 G is an almost columnar member having a substantially constant outer diameter, and the outer diameter of the holding member  260 G is substantially the same as the outer diameter Φ 3  of the shaft  210 . The holding member  260 G is joined to the distal end portion of the shaft  210 . For the joining, any joining agent such as an epoxy adhesive can be used. As described above, the configuration of the light irradiation device  2 G can be modified in various ways, and may include the holding member  260 G having a different shape from that in the seventh embodiment. Also, the light irradiation system according to the eighth embodiment as described above makes it possible to exhibit an effect similar to those in the first and seventh embodiments described above. 
     Ninth Embodiment 
       FIG. 15  is an explanatory diagram illustrating a configuration of a light irradiation device  2 H according to the ninth embodiment. A light irradiation system according to the ninth embodiment includes the catheter  1  explained in the first embodiment and the light irradiation device  2 H illustrated in  FIG. 15 . The light irradiation device  2 H has a holding member  260 H having a shape different from that in the seventh embodiment, in the configuration in which the curved part  251  of the optical fiber  250 F explained in the seventh embodiment protrudes from the shaft  210 . The holding member  260 H includes a distal end side holding member  261 H and a proximal end side holding member  262 H. The distal end side holding member  261 H is disposed on the distal end of the light irradiation device  2 H to cover the distal periphery (entire surface in the circumferential direction) of the curved part  251  protruding from the shaft  210 . The proximal end side holding member  262 H is disposed between the distal end side holding member  261 H and the shaft  210  to cover the proximal periphery (entire surface in the circumferential direction) of the curved part  251  protruding from the shaft  210 . The distal end side holding member  261 H and the proximal end side holding member  262 H are both an almost columnar member having a substantially constant outer diameter. The outer diameter of the distal end side holding member  261 H and the outer diameter of the proximal end side holding member  262 H are both substantially equal to the outer diameter Φ 3  of the shaft  210 . As described above, the configuration of the light irradiation device  2 H can be modified in various ways, and may include the holding member  260 H having a different shape from that in the seventh embodiment. Also, the light irradiation system according to the ninth embodiment as described above makes it possible to exhibit an effect similar to those in the first and seventh embodiments described above. 
     Tenth Embodiment 
       FIG. 16  is an explanatory diagram illustrating a configuration of a light irradiation device  2 I according to the tenth embodiment. A light irradiation system according to the tenth embodiment includes the catheter  1  explained in the first embodiment and the light irradiation device  2 I illustrated in  FIG. 16 . The light irradiation device  2 I has a shaft  210 I instead of the shaft  210 , an optical fiber  250 I instead of the optical fiber  250 , and a light irradiation portion  239 I instead of the light irradiation portion  239 . 
     Similarly to the shaft  210  according to the first embodiment, the shaft  210 I has a hollow and almost cylindrical shape in which both a distal end portion and a proximal end portion are opened. Unlike the shaft  210  according to the first embodiment, the shaft  210 I has no opening for exposing the distal end of the optical fiber  250 I. A portion of the shaft  210 I, on which the distal end of the optical fiber  250 I abuts, is made of a light transmissive resin, and configured to allow transmission of the laser light LT. Similarly to the optical fiber  250  according to the first embodiment, the optical fiber  250 I has the curved part  251  where the optical fiber  250 I is curved in the +Y-axis direction, on the distal end portion. Unlike the optical fiber  250  according to the first embodiment, the optical fiber  250 I is arranged such that its distal end (distal end surface) abuts on the inner peripheral surface of the shaft  210 I. The light LT emitted from the core  250   c  exposed on the distal end of the optical fiber  250 I is transmitted through the shaft  210 I and emitted to the outside. Thereby, in the tenth embodiment, a part of the shaft  210 I functionally serves as the light irradiation portion  239 I. 
     As described above, the configuration of the light irradiation device  2 I can be modified in various ways, and the distal end of the optical fiber  250 I need not be disposed so as to be exposed on the outer peripheral surface of the shaft  210 I. In this case, a portion of the shaft  210 I, on which the distal end of the optical fiber  250 I abuts, may have a thickness smaller than of the other portion to allow transmission of the light LT. In addition, a resin body or a light reflecting mirror for transmission, refraction, and amplification of the light LT may be disposed on the portion of the shaft  210 I, on which the distal end of the optical fiber  250 I abuts. The whole of the shaft  210 I may be formed of the light transmissive resin. Also, the light irradiation system according to the tenth embodiment as described above makes it possible to exhibit an effect similar to that in the first embodiment described above. 
     Eleventh Embodiment 
       FIG. 17  is an explanatory diagram illustrating a configuration of a light irradiation system according to the eleventh embodiment. The light irradiation system according to the eleventh embodiment includes the catheter  1  explained in the first embodiment and a light irradiation device  2 J illustrated in  FIG. 17 . The light irradiation device  2 J does not have the shaft  210 , the distal tip  220 , and the connector  240  explained in the first embodiment, and is composed of an optical fiber  250 J and a holding member  260 J. A configuration of the optical fiber  250 J is the same as of the optical fiber  250  explained in the first embodiment, and a configuration of the holding member  260 J is the same as of the holding member  260  explained in the first embodiment. In this way, the configuration of the light irradiation device  2 J can be modified in various ways, and need not include at least a part of each of the shaft  210 , the distal tip  220 , and the connector  240 . Also, the light irradiation system according to the eleventh embodiment as described above makes it possible to exhibit an effect similar to that in the first embodiment described above. In addition, in the light irradiation device  2 J according to the eleventh embodiment, the configuration of the light irradiation device  2 J can be simplified, so that the light irradiation device  2 J can be easily manufactured and a manufacturing cost of the light irradiation device  2 J can be reduced. In addition, when the diameter of the light irradiation device  2 J can be decreased, device delivery from a forceps port of a small diameter endoscope such as an oral endoscope or a nasal endoscope becomes possible. 
     Modifications of Embodiment 
     The disclosed embodiments are not limited to the above-described embodiments, and may be implemented in various modes without departing from the spirit of the disclosed embodiments. The following modifications can be applied, for example. 
     [First Modification] 
     In the first to eleventh embodiments above, examples of the configurations of the catheter  1 , and the light irradiation devices  2 , and  2 A to  2 J have been described. However, the configurations of the catheter  1  and the light irradiation device  2  can be modified in various ways. For example, the light irradiation system may be constituted by only the light irradiation device  2  without the catheter  1 . 
     For example, a reinforcing layer formed of a braided body or a coil body may be embedded in the shaft  110  of the catheter  1  and the shaft  210  of the light irradiation device  2 . Thus, it is possible to improve the torquability and the shape retention of the catheter  1  and the light irradiation device  2 . For example, a coating formed of a hydrophilic or hydrophobic resin may be applied to the outer surface of the catheter  1  and the outer surface of the light irradiation device  2 . Thus, the slidability of the catheter  1  in the living body lumen can be improved. Further, the slidability of the light irradiation device  2  in the lumen  110 L of the catheter  1  can be improved. Moreover, the outer surface of the catheter  1  or the outer surface of the light irradiation device  2  may be coated with an antithrombotic material such as heparin. This makes it possible to suppress a decrease in laser output due to thrombus adhesion to the inner and outer surfaces of the catheter  1  and the outer surface of the light irradiation device  2  caused by the irradiation with the emission light (laser light) LT. 
     For example, the catheter  1  may include an expansion portion expandable in a radial direction (YZ-direction). For example, a balloon formed of a flexible thin film or a mesh body having wires arranged in a mesh shape can be used as the expansion portion. The expansion portion may be provided on at least one of the distal end side of the light transmitting portion  139  and the proximal end side of the light transmitting portion  139  in the shaft  110 . Thus, after the catheter  1  is positioned in the living body lumen, the catheter  1  can be fixed in the living body lumen by expanding the expansion portion. Further, if a balloon is used as the expansion portion, the bloodstream at the site being irradiated with light can be blocked, and thus, it is possible to prevent that the bloodstream blocks the light. 
     For example, the catheter  1  may be configured as a multi-lumen catheter including a plurality of lumens different from the lumen  110 L. Similarly, the light irradiation device  2  may be configured as a multi-lumen catheter including a separate lumen different from the lumen into which the first optical fiber  250  is inserted. In this case, the shaft  210  can be made using a hollow member having a substantially cylindrical shape, and the distal tip  220  can be provided with a through-hole extending along the direction of the axis O. 
     For example, the inner surface of the distal tip  120  of the catheter  1  and the outer surface of the distal tip  220  of the light irradiation device  2  may be formed of a magnetic material and may be configured to attract each other. Thus, as illustrated in  FIG. 4 , a state where the light irradiation device  2  is inserted into the catheter  1  and the distal tip  220  is pressed against the distal tip  120  can be easily maintained. For example, it is allowed to adopt a configuration in which the distal tip  120  of the catheter  1  is omitted and the distal end side of the shaft  110  is opened. 
     [Second Modification] 
     In the above first to eleventh embodiments, regarding the light irradiation devices  2 , and  2 A to  2 J, examples of the configurations of the optical fibers  250 ,  250 F,  250 I, and  250 J, and the holding members  260 ,  260 A to  260 H, and  260 J have been described. However, these configurations can be modified in various ways. For example, the shape of the curved part  251  for allowing the distal end of the optical fiber  250  to intersect with the long axial direction of the light irradiation device  2  is not limited to the shape illustrated in the figures, and any shape can be adopted. For example, the optical fiber  250  may have a separate curved part different from the curved part  251  for allowing the distal end of the optical fiber  250  to intersect with the long axial direction of the light irradiation device  2 . This curved part can be disposed e.g. on the proximal end side of the curved part  251 . The shape of the curved part can be arbitrarily determined and may be e.g. a spiral shape, a wave shape, or a bellows shape, along the inner peripheral surface of the shaft  210 . 
     For example, longitudinal ranges (axis O direction) of the holding member  260  arranged adjacent to the periphery of the curved part  251 , the inner holding member arranged adjacent to the inner peripheral side of the curved part  251 , and the outer holding member arranged adjacent to the outer peripheral side of the curved part  251  can be arbitrarily determined. For example, the outer holding member arranged adjacent to the outer peripheral side of the curved part  251  may be disposed up to the distal end (boundary surface between the shaft  210  and the distal tip  220 ) of the shaft  210 . 
     For example, the light irradiation device  2  may include only the outer holding member arranged adjacent to the outer peripheral side of the curved part  251  without including the inner holding member arranged adjacent to the inner peripheral side of the curved part  251 . For example, as in the fifth embodiment, the outer holding member arranged adjacent to the outer peripheral side of the curved part  251  may include a first outer holding member disposed on the distal end side and a second outer holding member disposed on the proximal end side. The outer holding member arranged adjacent to the outer peripheral side of the curved part  251  may include three or more outer holding members. 
     [Third Modification] 
     In the first to eleventh embodiments described above, the examples of the configurations of the light transmitting portion  139 , and the light irradiation portions  239  and  239 I have been described. However, the configurations of the light transmitting portion  139  and the light irradiation portion  239  can be modified in various ways. For example, the light transmitting portion  139  may be formed of a radiopaque material, to integrally form the light transmitting portion  139  and the first marker portions  131  and  132 . Similarly, at least the distal end portion (light irradiation portion  239 ) of the clad  250   cl  may be formed of a radiopaque material to integrally form the light irradiation portion  239  and the second marker portions  231  and  232 . 
     For example, the light transmitting portion  139  may be formed by thinning a part of the shaft  110 . For example, at least one side of the light transmitting portion  139  may be formed as a notch (through hole that communicates between the inside and outside of the shaft) formed on the shaft  110 . In this way, the light transmitting portion  139  can be easily formed. For example, the range in the axis O direction (X-axis direction) and the range in the circumferential direction (YZ-axis direction), where the light transmitting portion  139  is disposed, can be arbitrarily changed. Specifically, for example, the light transmitting portion  139  may be disposed over a wide range in the axis O direction. 
     For example, the catheter  1  may further include a separate marker portion disposed at any position, such as the distal end side and the proximal end side of the light transmitting portion  139 . For example, the light irradiation device  2  may further include a separate marker portion disposed at any position, such as the distal end side and the proximal end side of the light transmitting portion  239 . The shapes of the marker portions of the catheter  1  and the light irradiation device  2  can be arbitrarily determined, and may be a shape extending over the whole or a part of the circumferential direction (YZ direction), a shape extending in the axis O direction (X-axis direction), or a shape surrounding the periphery of the shaft. In addition, the distal tip  120  of the catheter  1  or the distal tip  220  of the light irradiation device  2  may be configured as the marker portions. 
     [Fourth Modification] 
     The configurations of the catheter  1 , and the light irradiation devices  2 , and  2 A to  2 J according to the first to eleventh embodiments, and the configurations of the catheter  1 , and the light irradiation devices  2 , and  2 A to  2 J according to the first to third modifications may be combined as appropriate. For example, the configuration explained in the sixth embodiment (configuration not including the resin member  270 ) may include the holding member  260  explained in the second to fifth embodiments or the seventh to ninth embodiments. For example, the configuration explained in the tenth embodiment (configuration in which the distal end of the optical fiber  250  abuts on the inner peripheral surface of the shaft  210 ) may include the holding member  260  explained in the second to fifth embodiments or the seventh to ninth embodiments. For example, the configuration explained in the eleventh embodiment (configuration not including the shaft  210 , the distal tip  220 , and the connector  240 ) may include the holding member  260  explained in the second to fifth embodiments or the seventh to ninth embodiments. 
     Although the aspects have been described based on the embodiments and the modifications, the embodiments of the above-described aspects are for facilitating understanding of the aspects, and do not limit the aspects. The aspects can be modified and improved without departing from the spirit of the aspects and the scope of the claims, and equivalent aspects are included in the aspects. Further, unless a technical feature is described as essential in the present specification, the technical feature may be omitted as appropriate. 
     DESCRIPTION OF REFERENCE NUMERALS 
       1  . . . Catheter 
       2 ,  2 A to  2 J . . . Light irradiation device 
       3  . . . Light source 
       110  . . . Shaft 
       120  . . . Distal tip 
       131 ,  132  . . . First marker portion 
       139  . . . Light transmitting portion 
       140  . . . Connector 
       141  . . . Connection portion 
       142  . . . Blade 
       210 ,  210 I . . . Shaft 
       220  . . . Distal tip 
       231 ,  232  . . . Second marker portion 
       239 ,  239 I . . . Light irradiation portion 
       240  . . . Connector 
       241  . . . Connection portion 
       242  . . . Blade 
       250 ,  250 F,  250 I,  250 J . . . Optical Fiber 
       250   c  . . . Core 
       250   cl  . . . Clad 
       251  . . . Curved part 
       260 ,  260 A to  260 H,  260 J . . . Holding member 
       261 ,  261 C . . . Inner holding member 
       261 D . . . First inner holding member 
       261 H . . . Distal end side holding member 
       262 ,  262 C,  262 D . . . Outer holding member 
       262 H . . . Proximal end side holding member 
       263 D . . . Second inner holding member 
       270  . . . Resin member