Abstract:
An apparatus and method for tailoring the radiation intensity about a radiation source, enabling affected zones of a cancerous tissue mass to receive full radiation dosage while limiting the exposure of unaffected regions where radiation exposure is not desired. The assembly includes a radiation attenuator partially covering the outer periphery of a delivery portion of a high dosage radiation catheter, thereby altering the radiation profile that exits the assembly. A method for treating a cancer affected tissue mass includes inserting a plurality of said catheters into a tissue mass about the center of mass and orienting said catheter so that said the maximum radiation intensity is facing substantially toward the center of mass. The radiation source is allowed to dwell in the catheter for a prescribed period of time to deliver the desired dosage of radiation. The radiation source is then removed from the catheter.

Description:
PRIORITY CLAIM 
     The present application claims priority to U.S. Provisional Application Ser. No. 60/820,283, filed Jul. 25, 2006 and entitled “SHIELDED HIGH DOSE RADIATION CATHETERS, which is herein incorporated by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The invention is directed generally to the field of catheters. More specifically, the invention is directed to catheters and methods utilized in high dose rate temporary brachytherapy. 
     BACKGROUND OF THE INVENTION 
     Brachytherapy is a form of internal radiation treatment where radioactive sources are placed on or within cancerous tumors. There are two major forms of brachytherapy: permanent seed implantation, wherein radioactive seeds are permanently placed within a cancerous gland or tissue mass, and high dose rate (HDR) temporary brachytherapy, which involves the temporary placement of a high intensity radiation source within or in close proximity to the cancerous tumor. 
     HDR temporary brachytherapy is particularly suited for treatment of prostate, gynecologic, breast, head and neck, lung, esophageal, bile duct, anorectal and sarcoma cancers. Tiny plastic catheters are placed in the subject tissue mass for administration of a series of radiation treatments. A computer-controlled machine, often referred to as an “afterloader,” loads a highly radioactive seed, typically made of iridium, into each of the catheters in a serial fashion. The radiation dose delivered to a particular zone of the affected tissue mass may be tailored by altering the time the seed is allowed to dwell in a particular catheter—a significant advantage of HDR temporary brachytherapy over permanent seed implantation. The catheters are removed upon completion of the treatment series. 
     Minimization of exposure of certain regions of an affected tissue mass, as well as non-cancerous neighboring tissue, is typically desired during the HDR temporary brachytherapy. For example, in the treatment of prostate cancer, it is advantageous to minimize the exposure of the urethra and rectum during HDR treatment. Generally, directing the intensity of the radiation dose toward the cancerous tumor while reducing the intensity directed away from the tumor is desired. 
     SUMMARY OF THE INVENTION 
     An apparatus and method for tailoring the radiation intensity about a radiation source is disclosed. The apparatus and method enables the desired zones of the affected tissue mass to receive full radiation dosage while limiting the exposure of unaffected regions where radiation exposure is not desired. Embodiments of the invention thus permit increased intensities and dosages of radiation during a treatment session while mitigating damage to neighboring healthy tissues, thereby reducing the number of treatment sessions. 
     In one aspect, the present disclosure is directed to an HDR catheter apparatus comprising a hollow tubular element having a central axis and a distal end portion with an outer periphery, and a radiation source removably positioned in the distal end portion. A radiation attenuator partially covers the outer periphery of the distal end portion, defining a partially shrouded zone that alters the radial profile of the radiation intensity emitted by the radiation source. The uncovered portion of the outer periphery defines a window through which radiation passes relatively unattenuated. Other embodiments of the invention will be readily apparent to the skilled artisan. 
     In another aspect of the present disclosure, a method for treating a cancerous tissue includes selecting a plurality of the HDR catheters, each having a radiation attenuator that partially covers the outer periphery of a distal end portion, the uncovered portion of the outer periphery defining a window. Each of the HDR catheters are inserted into a region about the center of the cancerous tissue mass, and oriented so that the radiation window faces substantially towards the center of the cancerous tissue mass. A radiation source can then be routed through the hollow tubular element of one of the catheters and positioned within the partially shrouded zone at the distal end portion of the HDR catheter. The radiation source is allowed to dwell in the partially shrouded zone for a prescribed period of time to deliver the desired dosage of radiation to the affected zone of the cancerous tissue mass. The radiation source is then removed from the HDR catheter. The steps are repeated for each of the catheters in the tissue mass, with dwell times varying according to the dosage requirements. The method can further utilize one or more unattenuated catheters located near or within the center of mass of the cancerous tissue mass, or where the irradiation of neighboring zones is not a concern. 
     In still another aspect of this disclosure, a system for treating a cancerous tissue mass is described with an HDR catheter comprising a hollow tubular element having a central axis, a proximal end portion, a mid portion and a distal end portion with an outer periphery, and a radiation attenuator partially covering the outer periphery of the distal end portion. The radiation attenuator defines a partially shrouded zone of the distal end, and the uncovered portion includes a window portion. An afterloader including a radiation source is detachably connected to the proximal end of the HDR catheter. The proximal end of the HDR catheter is configured to receive the radiation source from the afterloader utilizing a drive wire that motivates the radiation source to or from the partially shrouded zone of the distal end portion through the proximal end portion and the mid portion. 
     The above summary of the various representative embodiments of the invention is not intended to describe each illustrated embodiment or every implementation of the invention. Rather, the embodiments are chosen and described so that others skilled in the art may appreciate and understand the principles and practices of the invention. The figures in the detailed description that follows more particularly exemplify these embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These as well as other objects and advantages of this invention, will be more completely understood and appreciated by referring to the following more detailed description of the presently preferred exemplary embodiments of the invention in conjunction with the accompanying drawings of which: 
         FIG. 1  depicts a temporary high dose radiation delivery system according to the present invention; 
         FIG. 2  is a perspective view of a catheter according to an embodiment of the invention; 
         FIG. 3  is a cross-sectional view of the catheter of  FIG. 1  taken at line  3 - 3  of  FIG. 2 ; 
         FIG. 4  depicts a distal end portion of an embodiment of an HDR catheter in cross-section; 
         FIG. 5  is a cutaway view of a distal end portion of an embodiment of an HDR catheter; 
         FIG. 6  depicts a distal end portion of an embodiment of an HDR catheter; 
         FIG. 7  is a cross-sectional view of the HDR catheter of  FIG. 6  taken at line  7 - 7 ; 
         FIG. 8  is a cross-sectional view of a tissue mass under treatment of multifocal cancer according to an embodiment of the invention; and 
         FIG. 9  is a cross-sectional view of a tissue mass under treatment of unifocal cancer according to an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Referring to  FIGS. 1 ,  2  and  3 , a high dose radiation delivery system  10  for an HDR catheter  12  with a retractable radiation source  14  is depicted. The HDR catheter  12  comprises a tubular element  16  having a central axis  17 , a proximal end portion  18 , a mid portion  20  and a distal end portion  22  having an outer peripheral surface  24  and a free end  26 . The free end  26  may be formed or fitted with a tip portion or cutting member  27 , as shown in phantom in  FIG. 2  to aid in insertion of the HDR catheter  12 . A lumen  28  passes through the proximal end portion  18 , mid portion  20  and into the distal end portion  22  of the HDR catheter, terminating near the free end  26  of the distal end portion  22 . 
     An afterloader  30 , such as the microSelectron™ afterloader manufactured by Nucleotron Corp., is used to drive the radiation source  14  into and out of the lumen  28  by way of a drive wire  32 . The afterloader  30  is connected to the proximal end portion  18  of the HDR catheter through a coupling  34  that readily disconnects from the HDR catheter. The coupling  34  may comprise a luer lock or a compression type fitting. The afterloader  30  is capable of placing the radiation source  14  into the distal end portion  22  of the HDR catheter. 
     The outer peripheral surface  24  defines an outer circumference or periphery  36  of the distal end portion  22  when viewed in cross-section ( FIG. 3 ). In one embodiment, a radiation attenuator  38  having an outer radial surface  35 , an arc length  37 , an axial length  39  and a thickness  41  is disposed on a portion of the outer peripheral surface  24  of the distal end portion  22 , covering only a portion of the outer periphery  36 . The radiation attenuator  38  thus delineates a partially shrouded zone  40  of the distal end portion  22  of the HDR catheter having an attenuated portion  42  that is covered by the radiation attenuator  38  and a window portion  44  defined by the uncovered portion of the outer periphery  36 . Preferably, the radiation attenuator  38  is made of a high density material such as lead or tungsten. 
     In operation, the afterloader  30  is connected to the HDR catheter, the radiation source  14  and the drive wire  32  are inserted into the lumen  28  at the proximal end portion  18  of the catheter, and the radiation source  14  is made to pass through the lumen  28  and to reside within the partially shrouded zone  40  of the distal end portion  22 . The radiation source  14  emits radiation  46  having a substantially uniform radial intensity profile about a central axis  48  of the radiation source  14  which is approximately coincident with the central axis  17  of the HDR catheter. 
     The presence of the radiation attenuator  38  creates a non-uniform radiation intensity profile  50  about the central axes  48  and  17  when the radiation source  14  is lodged in the partially shrouded zone  40 . A first or “unattenuated” portion  52  of the radiation intensity profile  50  passes through the window portion  44  of the partially shrouded zone  40  with little attenuation. A second or “attenuated” portion  54  of the radiation intensity profile  50  passes through the radiation attenuator  38 , thereby reducing the intensity of the second portion  54  of the emitted radiation  46  as it passes therethrough. Generally, there is a transition portion  55  of the radiation intensity profile  50  at the confluence between the unattenuated and attenuated portions  52  and  54 . The reduction in the intensity of the attenuated portion  54  of the emitted radiation  46  may be tailored by fabricating the radiation attenuator  38  from a material having an appropriate linear or mass attenuation coefficient, or by altering the thickness  41  of the radiation attenuator  38 , or some combination thereof. Moreover, the directional characteristics of emitted radiation  46  may be modified by altering the arc length  37  of the radiation attenuator  38 . 
     Accordingly, the radiation profile exiting the partially shrouded zone  40  of the HDR catheter can be tailored for significant reduction in the intensity of the attenuated portion  54 , enabling the catheter to deliver high doses of radiation in the direction of malignant tissue while significantly reducing the exposure of neighboring healthy tissue and organs. 
     Referring to  FIGS. 4 ,  5 ,  6  and  7 , other embodiments of the invention are presented. The embodiment depicted in  FIG. 4  portrays an HDR catheter  12  with a wall thickness  56  thick enough to accommodate an inset  58  in the distal end portion  22  of the HDR catheter  12  that accepts the radiation attenuator  38  so that the outer radial surface  35  of the radiation attenuator  38  is flush with the outer circumference  36  of the HDR catheter  12 . The embodiment of  FIG. 5  portrays the distal end portion  22  encapsulated in a shrink fit wrapper  60 . The  FIGS. 6 and 7  illustrations depict the distal end portion  22  of an HDR catheter  12  including a radiation attenuator  62  having transitional surfaces  64  and  66  and a lunately shaped cross-section  68 . 
     Functionally, the embodiments presented in  FIGS. 4 ,  5 ,  6  and  7  mitigate against damage to intervening tissue along the insertion path (not depicted) of the HDR catheter  12 . The flush relationship between the outer radial surface  35  of the radiation attenuator  38  and the outer circumference  36  of the HDR catheter  12  creates an essentially smooth surface that enables the intervening tissue material to part over the distal end portion  22  during insertion, removal and rotation of the HDR catheter  12  with less resistance and less damage to the neighboring or intervening tissue. Likewise, the shrink fit wrapper  60  provides a smooth, soft surface that enables a smooth parting of intervening tissue. The shrink fit wrapper  60  provides the additional advantage of isolating the radiation attenuator  38  from contacting the body tissue, thereby reducing toxicological concerns that contact with certain materials (e.g. lead) may pose. The transitional surfaces  64  and  66  and the lunately shaped cross-section  68  of the embodiments illustrate in  FIGS. 6  and  7  provide a similar functionality. The varying thickness across the arc length  37  of the lunately shaped cross-section  68  will also create a non-uniform attenuated radiation intensity  70  that may be desirable in certain instances. Other means that enable an exterior mounting of a radiation attenuator to an HDR catheter while mitigating the effects of abrupt surface transitions may also be utilized and will be apparent to those skilled in the art by virtue of this disclosure. 
     Referring to  FIGS. 8 and 9 , a method of using a plurality of the catheters  12  is described for the treatment of a tissue mass or gland  72  such as a prostate, breast, lung, esophagus or bile duct, anorectal and sarcoma having a center of mass  74 . Some cancers, such as prostate cancer, tend to be “multi-focal” in nature, and are typically but not always characterized by cancerous cells dispersed throughout an affected region. Other cancers, such as breast cancer, tend to be “unifocal” in nature; these cancers may be characterized by a cancerous zone, depicted in phantom by numerical reference  75  in  FIG. 9  that is to some extent delineated from healthy, non-cancerous tissues. 
     The treatment of a “multi focal” cancer is depicted in  FIG. 8 . A plurality of partially attenuated catheters  76 A- 76 H, each fabricated in accordance with the aforementioned embodiments of the present invention. Each of the catheters  76 A- 76 H is fitted with a radiation attenuator  38 . The partially attenuated catheters  76 A- 76 H are inserted into the tissue mass  72  and each is rotationally oriented so the respective window portion  44  faces toward the center of mass  74  of the tissue mass  72 . The rotational orientation of a given partially attenuated catheter  76 A- 76 H may be made before or after insertion into the tissue mass  72 . An unattenuated catheter  78  having no radiation attenuator is also inserted into the tissue mass  72  in or near proximity to the center of mass  74 , or in an area that may require a higher radiation dosage. 
     Once the tissue mass  72  is configured with the catheters  76 A- 76 H and  78  as depicted, a method of treatment of the tissue mass  72  is as follows (with reference back to  FIGS. 1 ,  2  and  3 ): The afterloader  30  is coupled to catheter  76 A and the radiation source  14  and the drive wire  32  are inserted into the lumen  28  at the proximal end portion  18  of the catheter  76 A. The radiation source  14  is pushed through the lumen  28  with the guide wire  32  and positioned so that it resides within the partially shrouded zone  40  of the distal end portion  22  of the catheter  76 A. The radiation source  14  remains within the partially shrouded zone  40  for a predetermined dwell period of time before being retracted from the lumen  28  with the guide wire  32 . Once the radiation source  14  is within the afterloader  30 , the afterloader  30  is disconnected from the partially attenuated catheter  76 A. This process may be repeated for some or all of the remaining catheters  76 B- 76 H and  78 . 
     Operationally, the orientation of the attenuators  38  in  FIG. 8  reduces the intensity of radiation that irradiates neighboring regions of the tissue mass  56  while irradiating the multifocal cancerous member with a substantially uniform dosage of radiation. Preferably, the radiation source  14  is passed through the lumen  28  with expediency to limit exposure of healthy tissue and organs located adjacent the catheters  76 A- 76 H and  78 . The dwell period that the radiation source  14  spends in the partially shrouded zone  40  of a given catheter  76 A- 76 H,  78  may be tailored to the dosage requirement of for the particular zone being irradiated. 
     The treatment of a unifocal cancer is depicted in  FIG. 9 . The HDR catheters  76 A- 76 H are inserted into the tissue mass or gland  72 , but are located in a more concentrated manner near the cancerous zone  75 . The catheters  76 A- 76 H are rotationally oriented to direct unattenuated radiation toward a center of mass  80  of the cancerous zone  75 . Again, an unattenuated HDR catheter may be placed within the tissue mass or gland  72 , preferably at or near the center of mass  80  the cancerous zone  75 . 
     Operationally, the orientation of the attenuators  38  in  FIG. 9  also reduces the intensity of radiation that irradiates the regions neighboring the tissue mass  56 , as well as the healthy, non-cancerous tissues of the tissue mass  56  itself, while irradiating the unifocal cancerous zone  75  with a substantially concentrated dosage of radiation. Again, the radiation source  14  is preferably passed through the lumen  28  with expediency to limit exposure of healthy tissue and organs located adjacent the catheters  76 A- 76 H and  78 . The dwell period that the radiation source  14  spends in the partially shrouded zone  40  of a given catheter  76 A- 76 H,  78  may be tailored to the dosage requirement of for the particular zone being irradiated. 
     While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiments, it will be apparent to those of ordinary skill in the art that the invention is not to be limited to the disclosed embodiments. It will be readily apparent to those of ordinary skill in the art that many modifications and equivalent arrangements can be made thereof without departing from the spirit and scope of the present disclosure, such scope to be accorded the broadest interpretation of the appended claims so as to encompass all equivalent structures and products.