Abstract:
A prostate immobilizing balloon that on full inflation cups the prostate to hold it during treatment is combined with a locking member so that the balloon does not shift during use. Methods of using same are also provided.

Description:
PRIOR RELATED APPLICATIONS 
       [0001]    This application is a continuation-in-part of Ser. No. 12/410,639 filed Mar. 25, 2009 (issued as U.S. Pat. No. 8,454,648). 
         [0002]    It is also a continuation-in-part of each of the following: Ser. No. 11/623,702 filed on Jan. 16, 2007 (ABD); Ser. No. 11/933,018 filed on Oct. 31, 2007 (ABD); Ser. No. 11/966,544 filed on Dec. 28, 2007 (ABD); Ser. No. 12/034,470 filed on Feb. 20, 2008 (U.S. Pat. No. 8,080,031); Ser. No. 12/141,270 filed on Jun. 18, 2008 (ABD); Ser. No. 12/410,639 filed on Mar. 25, 2009 (U.S. Pat. No. 8,454,648); Ser. No. 12/412,017 filed on Mar. 26, 2009 (ABD); Ser. No. 12/748,494, filed on Mar. 29, 2010 (U.S. Pat. No. 8,241,317); Ser. No. 13/299,348 filed on Nov. 17, 2011 (U.S. Pat. No. 8,679,147); Ser. No. 13/444,626 filed Apr. 11, 2012 (U.S. Pat. No. 8,603,129); Ser. No. 14/065,127 filed on Oct. 28, 2013 (pending); Ser. No. 14/198,087 filed on Mar. 5, 2014 (pending); Ser. No. 14/445,946 filed on Jul. 29, 2014 (pending), Ser. No. 14/517,932 filed on Oct. 20, 2014 (pending), and Ser. No. 12/707,389 filed on Feb. 17, 2010 (U.S. Pat. No. 8,500,771). Each of these U.S. applications is incorporated by reference in its entirety for all purposes. 
     
    
     FIELD OF THE DISCLOSURE 
       [0003]    The present disclosure relates to rectal balloons that are used for immobilizing the region surrounding the prostate. In particular, a rectal balloon with locking stopper is provided. 
       BACKGROUND OF THE DISCLOSURE 
       [0004]    Treatment of prostate cancer using radiation therapy is difficult due to the prostate&#39;s position near radiation-sensitive tissues, and is further complicated by prostate motion. Adenocarcinoma of the prostate commonly occurs in the posterior portion of the prostate gland, which is in very close proximity to the rectal wall. To date, external beam radiation treatment, urethrograms, CT scans and magnetic resonance imaging (MRI) have all been used to visually localize the prostate, as well as the normal critical structures in the surrounding area. 
         [0005]    U.S. Pat. No. 5,476,095 proposes an insertable pickup probe for use in providing diagnostic MRI images. The pickup probe, in its preferred embodiment, is proposed for use in imaging the male prostate and comprises an elongated shaft supporting an inflatable patient interface balloon at its distal end. The interface balloon comprises an inner balloon and an outer balloon, between which a receiving coil is positioned. A lumen for air supply is provided in the shaft for expanding the inner balloon against the outer balloon to place the receiving coil in close proximity to the area of interest in order to provide MRI images. 
         [0006]    Typically, the planning of radiation therapy for the treatment of prostate cancer involves the patient undergoing a CT-based simulation scan of the pelvis to determine the location of the prostate gland. In the simulation phase, the patient is placed on CT equipment that is preferably similar to the radiation treatment equipment (except that it does not generate the high energy radiation beam). The simulation equipment is positioned to simulate the delivery of the sequence of treatment beams prescribed by the treating oncologist. Normally, during the simulation procedure, CT images are acquired. These CT images allow the oncologist to locate the position of the tumor and help to facilitate the composition of a radiation treatment plan. This treatment plan delineates the positions of the radiation equipment components for delivery of the treatment beams. 
         [0007]    During the actual treatment phase, the patient is placed in the same position on the treatment equipment as in the simulation scans. Radiation-emitting devices are generally known and used for radiation therapy in the treatment of patients. Typically, a radiation therapy device includes a gantry, which can be swiveled around a horizontal axis of rotation in the course of a therapeutic treatment. A linear accelerator is located in the gantry for generating a high-energy radiation beam for therapy. During treatment, the radiation beam is provided by this equipment and is delivered to the patient at the precise location as delineated by the physician during simulation. A further feature of radiation therapy involves portal images, which are commonly used in radiation therapy to verify and record the patient tumor location. Portal images include manual (film) and electronic images (EPI) taken before and/or after the treatment. 
         [0008]    During external beam radiation therapy, radiation is directed to the target prostate, which is near the rectal wall. Typically, a plurality of beams are used, and where the beams cross the highest radiation is provided. A misdirected radiation beam may perforate the rectal wall causing radiation proctitus (rectal bleeding). This toxicity is related to the total radiation dose prescribed and the volume of the anterior rectal wall receiving a high radiation dose. A major factor limiting radiation oncologists&#39; attempts to reduce the volume of the anterior rectal wall receiving a high radiation dose is the position of the prostate gland as well as the intrinsic motion up to 5 mm in the anterior to posterior direction caused by rectal peristalsis. Accordingly, oncologists generally will add a margin to the radiation field in order to ensure that the entire prostate gland receives the prescription dose. This margin is typically on the order of 5 to 15 mm. As a consequence, lower doses of radiation may need to be used so as not to overexpose radiation sensitive healthy structures. However, this may lead to inadequate radiation treatment and a higher probability of local cancer recurrence. 
         [0009]    US20030028097 proposes an insertable probe for immobilizing a region of interest during staging and radiation therapy thereof. In particular, a balloon is proposed having a rectangular cross section connected to a shaft. The shaft extends to an end of the balloon so as to allow fluid flow through an interior of the shaft and into the balloon so as to selectively inflate the balloon once the balloon is installed into the rectal cavity. The balloon, shaft and handle are bonded together so that they move radially as a single unit when torque is applied. A syringe is provided which connects the shaft and serves as an air pump to deliver a volume-limited amount of air to the air lumen of the shaft to the balloon. A stop cock is provided to maintain the air within the balloon. 
         [0010]    One of the problems with the subject of US20030028097 is the discomfort associated with installing the rectal balloon within the rectal cavity. In particular, a relatively sturdy and wide diameter shaft is connected to a relatively large thick-walled balloon. Because the balloon is not supported by anything other than by the shaft, the balloon is formed of a relatively rugged and thick material. Because of the relatively large size of the shaft and the thick material of the rectangular-cross section balloon, the installation of the rectal balloon creates a large amount of discomfort for a patient. In addition, it is often difficult for the medical personnel to know exactly how far within the rectum the balloon has been installed. Thus, it is difficult to achieve a standardized and fixed position of the balloon during each and every use. The medical personnel must generally approximate the desired position of the balloon within the rectal cavity. As such, a need has developed whereby the rectal balloon can be formed of a minimal diameter shaft and of a balloon of relatively thin material. 
         [0011]    When the rectal balloon of US20030028097 is in an inflated condition, the outer surface is generally rounded. As such, the prostate will tend to balance on the curved (convex) surface rather than be properly seated thereon. Since seating is important for proper use, this device requires that the physician approximate a seated position rather than providing any feedback of the seated position. When the balloon is in an outwardly curved (convex) inflated condition, the prostate will have a tendency to slide to one side of the balloon or the other. As such, a need developed to provide a rectal balloon that retains the prostate in a proper seated position when the balloon is in a fully inflated condition. 
         [0012]    As discussed above, a very important consideration when treating patients using radiation therapy is that the proper dose of radiation reaches the treatment site. This is very important whether the treatment method utilizes implanted radiation seeds or external beams of radiation. Excessive dosing of the patient can lead to severe side effects including impotence and urinary incontinence. In fact, estimates provide that as many as half the patients treated suffer incontinence and/or impotence. A proper treatment plan should deliver an adequate amount of radiation to the treatment site while minimizing the dose delivered to the surrounding tissues, and thus minimizing these side effects. 
         [0013]    U.S. Pat. No. 6,963,771 describes a method, system and implantable device for radiation dose verification. The method includes (a) placing at least one wireless implantable sensor in a first subject at a target location; (b) administering a first dose of radiation therapy into the first subject; (c) obtaining radiation data from the at least one wireless implantable sensor; and (d) calculating a radiation dose amount received by the first subject at the target location based on the radiation data obtained from the at least one wireless sensor during and/or after exposure to the first administered dose of radiation to determine and/or verify a dose amount of radiation delivered to the target location. 
         [0014]    U.S. Pat. No. 7,361,134 proposes a method of determining the dose rate of a radiation source including locating three or more detectors in the vicinity of a source. Each of the detectors provides an output indicative of the amount of radiation received from the source and determines the location of the source from at least some of the detector outputs. International Pub. No. WO2008148150 proposes a semiconductor radiation sensor. 
         [0015]    US20090236510 proposes a radiation dosimeter for measuring a relative dose of a predetermined radiation type within a detection region by using a plurality of scintillating optical fibers. US20060094923 proposes a marker comprising a wireless transponder configured to wirelessly transmit a location signal in response to a wirelessly transmitted excitation energy. 
         [0016]    A significant cause of patient discomfort associated with rectal balloons of the prior art is the buildup of gas pressure when the balloon is inserted into the rectum. This buildup of gas pressure can also affect the ability to properly seat the balloon in a desired position. Furthermore, gas buildup is now known to cause a significant amount of prostate movement. Therefore, a device that could eliminate same would be of benefit in allowing margin reductions and thus fewer side effects. 
         [0017]    In addition, the rectal balloon is known to move with peristalsis, and movement of the balloon thereby can affect prostate immobilization. Anal clenching will also cause significant movement. Thus, a need exists for a rectal balloon apparatus that is prevented from moving during treatment. 
       BRIEF SUMMARY OF THE DISCLOSURE 
       [0018]    A rectal balloon apparatus comprises a shaft having a fluid passageway extending therethrough. A lumen may be positioned with or be integral to the shaft for movement of rectal gas or other rectal fluids. A flexible tip with one or more openings may be disposed on the end of the shaft and/or the rectal gas relieving lumen inserted into the rectum. The shaft may have a locking device that is slidable longitudinally along the shaft. The locking device may be locked at a desired indicia on the shaft to fix the amount of movement of the shaft into the rectum. In one embodiment, a splitting device disposed with the ends of the shaft and the rectal gas relieving lumen that are not inserted into the rectum may split the lumen from the fluid passageway of the shaft. The lumen port on the splitting device may have a luer lock device for placement of a lumen port cap to prevent the back flow of rectal fluids. A syringe may be positioned with the luer lock to flush the lumen. 
         [0019]    A balloon may be affixed over an end of the shaft such that the fluid passageway communicates with an interior of the balloon. The balloon can be converted from a non-inflated condition to an inflated condition. A radiation-detecting sensor may be positioned at any location with the balloon, the shaft, and/or the rectal gas relieving lumen for sensing the amount of radiation delivered. A motion detecting sensor may be positioned at any location with the balloon, the shaft, and/or the rectal gas relieving lumen for sensing the amount of motion or movement of the balloon or surrounding area, such as the part of the rectal wall near the prostate, the shaft, the rectal gas relieving lumen, the radiation sensor, any fiducial markers, and/or any other part of the apparatus. The balloon may have a generally laterally flat surface when in the inflated condition, with a longitudinal groove formed in the laterally flat surface. One or more fiducial markers may be positioned at any location with the balloon, the shaft, and/or the rectal gas relieving lumen. A fiducial marker may be positioned with the flexible tip at the end of the shaft and/or lumen inserted into the rectum. Other types of sensors may be positioned with the balloon, the shaft and/or the lumen. A processor may be used to interpret the information from the different sensors and fiducial markers. 
         [0020]    The invention includes one or more of the following embodiments in any and all possible combination(s) thereof:
       A locking stopper for a rectal balloon, the stopper having a hemispherical head portion with smoothly rounded surface adjacent the anus, and either a radially central hole or slit therethrough, such that the stopper can be positioned over a balloon shaft or lumen. A base portion of the stopper adjacent the head portion is connected to the head portion and has a hinge that snap closes, squeezing the device slightly over the balloon shaft, thus locking it into position during use. This is very different from other stoppers used on various medical tubing, because the hemispherical distal surface of the stopper is sized and shaped for a comfort fit against the anus, the size (1-2 inches in diameter) preventing further movement and the smoothly rounded surface providing comfort. As used herein, “hemisphere” means half of a sphere (e.g. a half an orange or egg), but perfect sphericity is not required, only that the surface be sufficiently rounded for comfort to delicate tissues.   A prostate immobilizing balloon, said balloon comprising: an inflatable balloon having a proximal end and a distal end; said balloon further comprising a depressed central seating area when fully inflated, wherein said central seating area retains the prostate in a seated position in said central seating area when said balloon is fully inflated and in use in a rectum of a patient; a first lumen communicating with an interior of said balloon, said first lumen having a closable valve; a locking member around said first lumen, said locking member being movable between a locked position and an unlocked position, said locking member having an inner surface suitable for gripping said first lumen when said locking member is in said locked position; a second lumen extending from past said proximal end of said balloon to past said distal end of said balloon, said second lumen having a closed distal tip and one or more ports adjacent said closed distal tip and distal to said balloon; and one or more fiducial markers on a surface thereof.   A locking device for use on a shaft of a prostate immobilizer comprising: a positioning member having a head portion and a stem portion, said stem portion extending from said head portion, said head portion and said stem portion having a channel formed therein, said channel suitable for receiving the shaft therein; and a locking member connected to said stem portion, said locking member being movable between a locked position and an unlocked position, said locking member having a surface suitable for gripping the shaft when said locking member is in said locked position; said head portion having a generally hemispherical shape at one end thereof and a generally flat surface at the opposite end thereof, and said locking member positioned adjacent to said generally flat surface.   Any locking device herein described, said locking member being hingedly connected to said stem portion.   Any locking device herein described, said stem portion having a lip formed thereon, said locking member having a latch formed thereon, said latch engaging said lip when said locking member is in said locked position.   Any locking device herein described, said stem portion having an outer surface flush with a surface of said head portion, said locking member having an outer surface flush with another surface of said head portion when in said locked position.   Any locking device herein described, said head portion having a longitudinal split formed therein so as to open to said channel, said longitudinal split having an opening suitable for allowing the shaft to pass therethrough and into said channel.   A locking device for use on a shaft of a prostate immobilizer comprising: a positioning member having a head portion and a stem portion, said stem portion extending from said head portion, said head portion and said stem portion having a channel formed therein, said channel suitable for receiving the shaft therein; a locking member connected to said stem portion, said locking member being movable between a locked position and an unlocked position; said locking member having a surface suitable for gripping the shaft when said locking member is in said locked position; said head portion having a generally hemispherical shape at one end thereof and a generally flat surface at the opposite end thereof, and said locking member positioned adjacent to said generally flat surface; said stem portion having a lip formed thereon, said locking member having a latch formed thereon, said latch engaging said lip when said locking member is in said locked position; said stem portion having an outer surface flush with a surface of said head portion, said locking member having an outer surface flush with another surface of said head portion when in said locked position.   A prostate immobilizing device, said device comprising: an inflatable balloon having a proximal end and a distal end; said balloon further comprising a depressed central seating area when fully inflated, wherein said central seating area retains the prostate in a seated position in said central seating area when said balloon is fully inflated and in use in a rectum of a patient; a first lumen communicating with an interior of said balloon, said first lumen having a closable valve; any locking member herein described around said first lumen.   Any prostate immobilizing device as herein described, a second lumen extending from past said proximal end of said balloon to past said distal end of said balloon, said second lumen having a closed distal tip and one or more ports adjacent said closed distal tip and distal to said balloon.   Any prostate immobilizing device as herein described, further comprising one or more fiducial markers on a surface thereof, preferably a fiducial marker on a distal tip thereof.   A method of treating prostate cancer by external beam radiation therapy (XRT), comprising: inserting a prostate immobilizing balloon of herein described into a rectum of a patient with a cancerous prostate; inflating said balloon sufficiently to immobilize said prostate in said central seating area; locking said locking member adjacent an anus; and treating said prostate with XRT.   A method of treating prostate cancer by external beam radiation therapy (XRT), comprising: inserting a prostate immobilizing balloon as described into a rectum of a patient with a cancerous prostate; allowing rectal gas to exit the rectum via said one or more ports until no further exiting gas is evident; inflating said balloon sufficiently to immobilize said prostate in said central seating area; locking said locking member adjacent an anus; treating said prostate with XRT; and allowing rectal gas to exit the rectum via said one or more ports during said treating step.   A method of treating prostate cancer by external beam radiation therapy (XRT), comprising: inserting a prostate immobilizing balloon of claim  9  into a rectum of a patient with a cancerous prostate; allowing rectal gas to exit the rectum via said one or more ports until no further exiting gas is evident; inflating said balloon sufficiently to immobilize said prostate in said central seating area; determining the position of said one or more fiducial markers and positioning said balloon such that said fiducial markers are in a desired position; locking said locking member adjacent an anus; treating said prostate with XRT; and allowing rectal gas to exit the rectum via said one or more ports during said treating step.   A prostate immobilizing balloon, said balloon comprising: an inflatable balloon having a proximal end and a distal end; said balloon being sized and shaped for use in a rectum (about 100-120 cc, and about 1-1.5×3-4 inches); a first lumen communicating with an interior of said balloon, said first lumen having a closable valve; the locking member as described around said first lumen.   A method of treating prostate cancer by external beam radiation therapy (XRT), comprising: inserting the prostate immobilizing balloon of claim  14  into a rectum of a patient with a cancerous prostate; inflating said balloon sufficiently to immobilize said prostate; locking said locking member adjacent an anus; and treating said prostate with XRT.   Any prostate immobilizing balloon, said locking member having a hemispherical distal surface for comfortably positioning adjacent an anus when in use.   A method of treating prostate cancer by external beam radiation therapy (XRT), comprising: inserting a prostate immobilizing balloon as herein described into a rectum of a patient with a cancerous prostate; allowing rectal gas to exit the rectum via said one or more ports until no further exiting gas is evident; inflating said balloon sufficiently to immobilize said prostate in said central seating area; determining the position of said one or more fiducial markers and positioning said balloon such that said fiducial markers are in a desired position; locking said locking member adjacent an anus; treating said prostate with XRT; and allowing rectal gas to exit the rectum via said one or more ports during said treating step.       
 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0039]    A better understanding of the present disclosure can be obtained with the following detailed descriptions of the various disclosed embodiments in the drawings: 
           [0040]      FIG. 1  is a side elevational view showing a rectal balloon apparatus in an uninflated condition. 
           [0041]      FIG. 2  is a side elevational view of a rectal balloon apparatus in an inflated condition. 
           [0042]      FIG. 3  is an isolated view showing the compact folding of the balloon over the end of the shaft. 
           [0043]      FIG. 4  is a top view of an inflated balloon showing the application of fiducial markers, radiation detecting sensors, and motion detecting sensors. 
           [0044]      FIG. 5  is a side view, partially transparent, of a balloon in a first inflated condition. 
           [0045]      FIG. 6  is a side view, partially transparent, of a balloon in a second inflated condition. 
           [0046]      FIG. 7  is a side view of a locking device in the locked position with the rectal balloon apparatus positioned within the anal canal. 
           [0047]      FIG. 7A  is a perspective isolated view of the locking device in the unlocked position. 
           [0048]      FIG. 8  is side view of the balloon of the rectal balloon apparatus positioned within the rectum and in an inflated condition. 
           [0049]      FIG. 9  is side view of the balloon of the rectal balloon apparatus in an inflated condition. 
           [0050]      FIG. 10  is side view, partially transparent, of a balloon in the inflated condition with a rectal gas relieving lumen integral with a shaft, and radiation detecting sensors and motion detecting sensors positioned with the balloon. 
           [0051]      FIG. 11  is side view of a balloon in the inflated condition with a rectal gas relieving lumen inside the fluid passageway of a shaft, a splitting device, and a lumen port cap positioned with the lumen port of the splitting device. 
           [0052]      FIG. 12  is an enlarged view of the balloon of  FIG. 11 . 
           [0053]      FIG. 13  is an enlarged view of the splitting device of  FIG. 11  showing the lumen port cap disposed with a luer lock. 
           [0054]      FIG. 14A  Mean frequency of rectal gas according to region and type of ERB used. The mean incidences of gas in one or more regions and in the anterior region differedat statistically significant levels (p&lt;0.00001 and p&lt;0.0000001, respectively) between the standard and gas-release ERBs. Error bars represent the standard deviation of the mean of within patient means. 
           [0055]      FIG. 14B  size of gas pockets. From Wooton 2012. 
           [0056]      FIG. 15  perspective of a gas release balloon cut about half way showing exterior lumen having holes along its length, thus allowing the release of gas trapped along the balloon. 
       
    
    
     DETAILED DESCRIPTION 
       [0057]      FIG. 1  shows a rectal balloon apparatus  10  comprising a shaft  12  having a fluid passageway extending therethrough. A balloon  14  is affixed over the end  16  of the shaft  12 . The balloon  14  is shown in an uninflated or deflated condition. The fluid passageway of the shaft  12  can communicate with the interior of the balloon  14 . Also shown is the locking device  13 , which is shown in more detail in  FIGS. 7 and 7A  and discussed below in detail therewith. The locking device  13  serves to assure reproducibility in the positioning of the balloon  14  during radiation therapy. 
         [0058]    The shaft  12  may be a generally longitudinal shaft, which has the fluid passageway extending through the center thereof. As used herein, fluid may mean gas, such as air, or liquid, such as water or saline. The shaft  12  is preferably made of a flexible material. A valve assembly  22  may be affixed to the shaft  12  opposite the balloon  14 . The valve assembly  22  can have a variety of configurations.  FIG. 1  illustrates the valve assembly  22  as an inline valve assembly configuration. The valve assembly  22  may also be an angled valve assembly configuration. The valve assembly  22  includes a stopcock  26 . A valve  28  facilitates the ability of the stopcock  26  to open and close so as to selectively allow the fluid to pass into the shaft  12 . A port  30  allows the valve assembly  22  to be connected to a supply of the fluid. When the stopcock  26  is opened by the rotation of the valve  28 , the fluid will flow through the valve assembly  22 , through the interior passageway of the shaft  12  and into the interior of the balloon  14 . The valve  28  can then be closed so as to maintain the inflated configuration of the balloon  14 . When the procedure is finished and the fluid needs to be removed from the balloon  14 , the valve  28  of stopcock  26  can then be opened so as to allow for the release of fluid therethrough. 
         [0059]    The opposite end  16  of the shaft  12  may contact the end  32  of the balloon  14 . The end  16  may be suitably curved (rounded or dome-shaped) so as to allow the shaft  12  to facilitate the introduction of the balloon  14  into the rectal cavity. The shaft  12  may have indicia  34  formed therealong. It can be seen that the indicia  34  has numerical references associated therewith. These numerical references are indicative of the distance that the balloon  14  has been inserted into the rectum. As such, the indicia  34  provide a clear indication to the medical personnel of the desired location of the rectal balloon  14 . An anal dilator ring  19  is shown adjacent an end of the balloon  14 . 
         [0060]      FIG. 2  illustrates an isolated view of the apparatus  10  after being installed within the rectum. The fluid can be introduced through the valve assembly  22  and through the interior passageway of the shaft  12  so as to inflate the balloon  14 . The balloon  14  may have a seating area  15  so that the prostate can be properly positioned thereon. When the balloon  14  is installed and inflated (˜100 cc), the prostate may reside on the flat surface  15  in a seated position. After the procedure has been completed, the balloon  14  can be deflated and easily pulled outwardly of the rectum in its deflated condition. In  FIG. 2 , it can be seen that the locking device  13  has been moved along the shaft  12  (from its position in  FIG. 1 ) to indicia  34 , specifically at the number “20.” This serves to assure that the balloon  14  will be in a proper position during subsequent radiation treatments. 
         [0061]      FIG. 3  shows that the balloon  14  is neatly folded and compressed over the outer diameter of the shaft  12 . The shaft  12  may have a rounded end abutting the end  32  of the balloon  14 . As such, a comfortable rounded profile may be provided at this end  32 . The balloon  14  may be pre-vacuumed during production to produce a minimal profile during use. The anal dilator ring  19  is placed over the shaft  12 . 
         [0062]      FIG. 4  is a top view of the balloon  14  showing the area of the balloon  14  that preferably engages with the prostate. Central seating area  46  for the prostate is shown as having a groove  52  formed thereon. The groove  52  may be generally rectangular-shaped and may engage with the tip of the prostate, reducing lateral motion. Other configurations of the groove  52  are contemplated. The central seating area  46  and the groove  52  enhance the holding stability of the balloon  14 . The head portion  17  of the balloon  14  may be generally tapered. This shape makes insertion of the balloon  14  into the rectum easier for medical personnel and more comfortable for the patient. The balloon  14  may have a thermally welded bond  53  connecting it to the shaft  12 . Other forms of bonding are also contemplated. 
         [0063]    A first radiation detecting sensor  70  may be located within the groove  52  of the central seating area  46 . The sensor  70  allows the treating physician to determine the real time delivery dose of radiation being received at the treatment area when the balloon  14  is in place. The sensor  70  may located in the middle of the groove  52 . This location is ideally centrally located on the prostate when the balloon  14  is in place. However, the radiation detecting sensor  70  may be positioned at any other location with the balloon, the shaft, or a rectal gas relieving lumen (not shown). A second radiation detecting sensor  70 B is shown disposed with the shaft, and a third radiation detecting sensor  70 A is shown positioned with the balloon surface. A radiation detecting sensor may be positioned with any surface of the balloon, the shaft, or a rectal gas relieving lumen. It is also contemplated that a radiation detecting sensor may be positioned unattached in the interior of the balloon. 
         [0064]    As shown in  FIG. 5 , a fourth radiation detecting sensor  70 C is positioned on the curved surface  44  of the balloon that is not adjacent the treatment area. Although only one radiation detecting sensor is preferably used, it is contemplated that more than one radiation sensor  70 ,  70 A,  70 B,  70 C may be used. By positioning the sensor(s)  70 ,  70 A,  70 B,  70 C near or adjacent to the prostate or other targeted anatomies, an accurate measurement of the radiation delivered to the prostate and/or other targeted anatomies, such as seminal vesicles, may be achieved. The sensors  70 ,  70 A,  70 B,  70 C can be chosen from any of the available sensors that enable the user to monitor radiation dosage. International Pub No. WO 2008/148150 proposes the preferable type of semiconductor radiation sensor that is contemplated. U.S. Pat. No. 7,361,134 also proposes a type of radiation sensor that is contemplated. It is also contemplated that a radiation sensor using scintillating fiber optics may be used. The sensor  70 ,  70 A,  70 B,  70 C may be positioned with the balloon, the shaft, or the gas relieving lumen with an adhesive, such as an epoxy glue. However, other attachment means are contemplated as are known in the art. 
         [0065]    Six fiducial markers  72  are shown positioned with the balloon  14 . Although a plurality of markers  72  are shown, it is contemplated that there may be only one or more fiducial markers  72 . It is contemplated that one or more fiducial markers  72 A may be positioned anywhere with the balloon, the shaft, or the gas relieving lumen (not shown). A fiducial marker  72 A is shown positioned at the very end of the shaft. The fiducial markers  72 ,  72 A may be made of a tungsten material, which may be detected by an MRI or CT scan. Other materials that may be visible on an MRI or CT scan are also contemplated, such as barium sulfate. Fiducial markers in powder or liquid form are contemplated. Through the use of these fiducial markers  72 ,  72 A on the balloon  14  or shaft  12 , a treating physician may get a clear image of the position of anterior and posterior walls of the rectum, and/or the position of the rectum relative to the prostate. Fiducial markers  72  may be positioned in spaced relation to each other with the top surface of the balloon  14 . For illustrative purposes, three of the fiducial markers  72  are positioned in linear alignment on one side of the groove  52 . Another three fiducial markers  72  are arranged on the opposite side of the groove  52 . Other combinations and locations of markers  72 ,  72 A are contemplated. A further benefit can be realized by utilizing an additional fiducial marker in the form of a gold seed marker implanted into the prostate. The gold seed marker combined with the fiducial markers  72  allows for triangulation to make certain that the balloon, rectum, and prostate are in the correct positions for treatment. 
         [0066]    A first motion detecting sensor  73  is shown within the groove  52  of the central seating area  46 . The motion detecting sensor  73  allows the treating physician to determine the movement of any of the radiation sensors  70 ,  70 A,  70 B,  70 C, fiducial markers  72 ,  72 A, the shaft, the gas relieving lumen, the balloon surface and the surrounding area, such as the part of the rectal wall near the prostate, and/or any other part of the apparatus. Although the motion detecting sensor  73  is shown in the groove  52 , one or more motion detecting sensors  73  may be positioned at any other location with the balloon, the shaft, or the gas relieving lumen (not shown). A second motion detecting sensor  73 A is shown placed at a different location with the surface the balloon. As shown in  FIG. 5 , a third motion detecting sensor  73 B may be positioned with the curved surface of the balloon that is not adjacent the treatment area. Although only one motion detecting sensor is preferably used, it is contemplated that more than one motion detecting sensor  73 ,  73 A,  73 B may be used. The motion detecting sensors  73 ,  73 A,  73 B may be selected from any of the available sensors that enable the user to detect motion. It is contemplated that disposable sensors may be used. It is also contemplated that an electromagnetic type motion detecting sensor may be used. Other types of sensors are contemplated. 
         [0067]      FIG. 5  is an isolated view of the balloon  14  as inflated to a first inflated condition. In this condition, the balloon  14  has a central seating portion  46 , a head portion  17  and a posterior portion  44 . When inflated, the central seating area  46  has a lateral flatness for the prostate to rest upon. The lateral flatness of the seating area  46  will prevent the prostate from sliding to one side or the other, and not deform the prostate. The bottom portion  44  is rounded and contacts the rectal wall. The head portion  17  is generally tapered so as to facilitate easier insertion of the balloon  14 . The material of the balloon  14  may be formed of a non-latex material, such as medical grade polyurethane, so as to avoid allergic reactions. The shaft  12  is shown extending into the interior of the balloon  14 . A plurality of holes  48  may be formed in the shaft  12  through which the balloon  14  is filled with air or other fluid. 
         [0068]    For all embodiments shown in all Figures, the balloons, such as balloon  14  in  FIG. 5 , may have a posterior or bottom portion, such as bottom portion  44 , that is made from a different thickness film material than the seating portion, such as seating portion  46 . By way of example, the posterior (bottom) portion  44  may be made with a thicker material than the seating (top) portion  46 . The thicker material may allow a support structure for the balloon  14 , and the thinner material may allow for the seating portion  46  to maintain its shape or have a distal bulge, such as bulge  47  shown in  FIG. 6 . It is also contemplated that the posterior portion  44  may be thinner than the seating portion  46 . The balloon may be made from two or more materials with different thicknesses attached together, such as by thermally welded bond. It is also contemplated that the balloon may be made from two or more materials with the same thickness but with different elasticity properties, such as different modulus of elasticity. 
         [0069]    It can be seem that each of the holes  48  is spaced from and offset by 90° from an adjacent hole around the diameter of shaft  12 . Other arrangements and orientations are contemplated. A total of six holes may preferably be formed in the shaft  12  within balloon  14  so as to allow the fluid to pass from an interior of shaft  12  to the interior of the balloon  14 . Other numbers of holes are contemplated. This arrangement of holes  48  facilitates complete extraction of the fluid from the balloon  14 . Under certain circumstances, one of the holes may become clogged or blocked by contact between the body and the balloon, and the staged arrangement assures that the unblocked holes  48  allow the fluid to continues to be easily extracted. In  FIG. 5 , it can be seen that additional fiducial markers  72  are positioned on the opposite side of balloon  14 . 
         [0070]      FIG. 6  is an isolated view of the balloon  14  as inflated to a second, more inflated condition (˜120 cc). In the second inflated condition, the balloon  14  has a first bulge  47  formed at the head portion  17 . The balloon also has a laterally flat seating portion  46 . The distal bulge  47  can be utilized in certain conditions to better isolate the prostate and stabilize the seminal vesicles. 
         [0071]    Turning to  FIG. 7 , the prostate immobilizer  10  has a shaft  12  having a fluid passageway  64  extending therethrough, a balloon  14  extending over an end  16  of the shaft  12  such that the fluid passageway  64  communicates with an interior  66  of the balloon  14 , a rectal gas relieving lumen  60  extending within the shaft  12  so as have an end  62  opening adjacent an end  68  of the balloon  14 , and a locking device  13  for locking a position of the shaft  12  of the prostate immobilizer  10 . The device  13  is adjustably slidable along the shaft  12 . The device  13  serves to assure uniformity in the positioning of the balloon  14  in the rectal cavity  2  adjacent the prostate  3  during radiation therapy. 
         [0072]    The end  16  of the shaft  12  is adjacent the end  68  of the balloon  14 . The end  16  of the shaft  12  is suitably rounded so as to allow the shaft  12  to facilitate the introduction of the balloon  14  into the rectal cavity  2 . The prostate immobilizer  10  is inserted into the rectal cavity  2  through anus  1 . The shaft indicia  34  has numerical references associated therewith. The numerical references are indicative of the distance that the balloon  14  is inserted into the anus  1 . The indicia  34  provide a clear indication to medical personnel of the position of the balloon  14  in the rectal cavity  2  for repeatability for subsequent treatments. The balloon  14  can be removed and re-inserted into the rectal cavity  2 . The locking device  13  is affixed to the shaft  12  so that the balloon  14  will be repositioned for a same distance into the rectal cavity  2  adjacent the prostate  3 . 
         [0073]    The locking device  13  is shown as positioned where indicia  34  number “25”. The anal dilator ring  19  is affixed to the shaft  12  adjacent the balloon  14 . The anal dilator ring  19  may displace the anal verge so as to displace the anal tissue and delineate the anatomy. The anal dilator ring  19  has a diameter greater than a diameter of the shaft  12 . 
         [0074]    Once the balloon  14  is positioned in a desired location adjacent the prostate  3 , medical personnel position the locking device  13  so that it is adjacent the anus  1  and holds the prostate immobilizer  10  in position. The balloon  14  is shown in an inflated condition. The seating area  15  is positioned adjacent the prostate  3  when in the rectal cavity  2 . The prostate immobilizer  10  is inserted and removed from the anus  1  in the deflated condition. The lateral flatness of the seating area  15  resists and inhibits the prostate  3  motion. The rounded outer surface of the balloon  14  generally contacts the wall of the rectal cavity  2 . The balloon  14  can be formed of a non-latex material, such as polyurethane, so as to avoid allergic reactions. 
         [0075]    The gas relieving lumen  60 , although shown on the interior of the shaft  12 , can be in any other orientation, such as on the outer surface of the shaft  12 , that allows for the removal of rectal gas, but preferably is integral with or immediately adjacent the fluid filling shaft. End  62  of the lumen  60  has one or more openings that allow for rectal gas or other bodily fluids to escape from the rectal cavity  2  and out of the lumen  60 . A one-way valve can be included along the length of the lumen  60  so as to only allow rectal gas or other bodily fluids to pass from the rectal cavity  2  to the outside environment through the gas relieving lumen  60 . The interior of the shaft  12  may be in fluid communication with the interior  66  of the balloon  14  so as to allow fluids to pass into and out of the interior  66  of the balloon  14  for inflation and deflation. 
         [0076]    During subsequent radiation treatments, the locking device  13  can be affixed to the shaft  12  in the same position as shown in  FIG. 7 . As such, when the balloon  14  is inserted, the shaft  12  can be urged forward until the locking device  13  contacts the entrance of the anus. The medical personnel may thus be confident that the balloon  14  is in the proper position. This is accomplished accurately regardless of any change of medical personnel, any squeezing of the sphincter muscles by the patient, and any variations in the amount of lubrication jelly that is used. Repeatability is typically assured. Reproducibility is particularly important when a radiation sensor is used in conjunction with the balloon. It is desirable that the radiation detecting sensor be in the substantially same location each time that it is detecting radiation. When the locking device is affixed to the shaft, it will not be easily displaced. The smooth contour of the outer surface contacting the anus provides comfort to the patient. 
         [0077]    In  FIG. 7A , the locking device  13  is in an unlocked position prior to attaching to the shaft  12  (not shown). The device  13  has a positioning member  18  and a locking member  38 . The positioning member  18  has a head portion  20  and a stem portion  320 . The stem portion  320  is integrally formed adjacent an end  24  of the head portion  20 . The positioning member  18  has a channel  340  formed therein. The channel  340  extends through each of the head portion  20  and the stem portion  320 . The positioning member  18  has a longitudinal split  36  formed therein. The longitudinal split  36  extends through the head portion  20 . The longitudinal split  36  communicates with the channel  340 . The locking member  38  has a locked position and an unlocked position. The locking member  38  is hingedly connected to the stem portion  320  of the positioning member  18 . The head portion  20  of the positioning member  18  has a hemispherical shape. The stem portion  320  of the positioning member  18  has an outer surface flush with an outer surface of the head portion  20 . The longitudinal split  36  extends for the entire length of the head portion  20 . The longitudinal split  36  has a width slightly greater than the diameter of the shaft  12 . This allows the shaft  12  to be introduced into the channel  340 . The channel  340  is sized so as to friction fit the shaft, or the channel can have protrusions to fit the shaft such that closing the device locks it in place. 
         [0078]    The stem portion  320  has an outer surface  40  that is flush with an outer surface of the head portion  20 . As such, the locking device  13  has smooth contours on the outer surface thereof. The stem portion  320  has a lip  480  extending and angling upwardly and outwardly of the outer surface  40 . The lip  480  is generally adjacent to the wall of the longitudinal split  36  of the head portion  20 . A curved surface  470  is formed on the interior of the stem portion  320  and has a plurality of ribs formed thereon. The curved surface  470  devices a portion of the channel  340 . The longitudinally-extending ribs on the curved surface  470  of channel  340  provide a structure that can suitably grip the outer surface of the shaft so as to facilitate the ability to fix the position of the locking device  13  on shaft  12 . Alternatively, the interior can be smooth but made of a tacky material that grips the shaft and/or lumen. 
         [0079]    The locking member  38  is hingedly connected to the stem portion  320 . The locking member  50  includes a latch  50  that has an edge that will engage the lip  480  of the stem portion  320 . The inner surface  51  of the locking member  50  includes a curved area  53 . Curved area  53  has ribs to grip and generally corresponds with the location of the curved surface  470  of stem portion  320 . As such, curved area  53  will cooperate with the curved surface  470  so as to define the channel  340  of the positioning member  18  when the locking member  38  is in a locked position. The locking member  38  also has an inner surface  52  which will reside in proximity with the end  24  of the head portion  20 . 
         [0080]      FIG. 8  shows an anatomical side view of the rectal balloon apparatus  10  positioned within a patient&#39;s rectum, as it would be during use. The balloon  14  is shown in an inflated condition and positioned up against and between the anterior wall  92  and the posterior wall  94  of the rectum  96 . It can be seen that the balloon  14  is positioned adjacent the prostate  90 , and that the balloon has been inflated enough to expand the rectum significantly. The fully inflated balloon thus compresses the prostate, tending to immobilize it in position adjacent the inflated balloon, and this reduction in motion allows the treating physician to reduce the treatment margins, thus irradiating less healthy tissue. Further, we now have clinical evidence, that the gas releasing lumen, which allows gas to escape during treatment, even further reduces the mobility of the prostate over a similar balloon lacking the gas release feature, allowing a further reduction in treatment margins. 
         [0081]    Additionally, it can be seen that a radiation detecting sensor  70  and a motion detecting sensor  73  are generally positioned adjacent the anterior wall  92  of the rectum  96 . It is also contemplated that a plurality of fiducial markers may also be positioned adjacent the anterior wall and/or the posterior wall  94  of the rectum  96 , and the balloon position adjusted as needed to ensure reproducible positioning as determined by visualizing the location of the fiducial markers. Thus, when a treating physician can determine the position of the plurality of fiducial markers he or she may obtain a clear image of the contours of the anterior wall  92  and the posterior wall  94  of the rectum  96  by essentially “connecting the dots.” The radiation sensor  70  may be used to detect the amount of radiation being received by the target areas, such as the rectal-prostate interface. The motion detecting sensor  73  may detect the movement of any of the sensors, markers, balloon surface or surrounding area, balloon shaft, or other part of the apparatus, allowing the balloon to be repositioned if needed.  FIG. 8  also shows the importance of the flexible aspect of the shaft  12  (which allows the technician to move the shaft as needed for filling etc. without inadvertently changing the position of the balloon) and the utilization of the locking device  13 . The locking device  13  and numerical indicia provides an initial indication of the depth of positioning of the balloon  14 . Thus, the device can be inserted to the same depth with every treatment, and then locked in place against further ingress. The lateral flatness of the balloon  14  is thereby assuredly positioned adjacent the prostate. 
         [0082]    The radiation detecting sensor  70  is thereby attempted to be positioned at the same location during all treatments. The sensor  70  can then be used to determine the amount of radiation delivered during each treatment, both daily radiation doses and accumulative radiation for the course of treatment. Treatment is of course halted when the proper radiation level or dosage has been reached. 
         [0083]      FIG. 9  is a side view of a rectal balloon apparatus  110  having a balloon  114  with a rectal gas relieving lumen  116  positioned with a surface of the shaft  112 . The gas release lumen  116  extends to an exterior of the balloon  114 . First opening  118  allows rectal gas or other fluids to pass from an exterior of the balloon  114  into the lumen  116 . The rectal gas passes through the lumen  116  to another opening at the opposite end of the lumen  116 , and into the atmosphere. The lumen  116  will have a portion extending interior of the balloon  114 . The ends of the balloon  114  will be sealed around the lumen  116  and the shaft  112 . A flexible lumen tip with ports (or holes), like lumen tip  156  shown in  FIG. 12 , may be positioned over first opening  118 . The flexible lumen tip with ports may provide for patient comfort when the shaft  112  is inserted into the rectum, and also serve to minimize fecal material from entering and clogging or obstructing the gas release lumen  116 . 
         [0084]    A first radiation detecting sensor  140  may be located with the balloon  114 . The sensor  140  is preferably located adjacent the prostate when the balloon  114  is in place. However, the radiation detecting sensor  140  may be positioned at any other location with the balloon  114 , the shaft  112 , or the lumen  116 , including the flexible lumen tip, such as tip  156  in  FIG. 12 . A second radiation detecting sensor  140 A is shown disposed with the shaft, and a third radiation detecting sensor  140 B is shown positioned with the lumen. It is also contemplated that a radiation detecting sensor may be positioned unattached in the interior of the balloon. As shown in  FIG. 10 , a fourth radiation detecting sensor  140 C may be positioned on the surface of the balloon that is not adjacent the treatment area. International Pub No. WO 2008/148150 proposes a type of semiconductor radiation sensor that is contemplated. U.S. Pat. No. 7,361,134 also proposes a type of radiation sensor that is contemplated. It is also contemplated that a radiation sensor using scintillating fiber optics may be used. Although only one radiation detecting sensor is preferably used, it is contemplated that more than one radiation sensor  140 ,  140 A,  140 B,  140 C may be used. 
         [0085]    Six fiducial markers  142  are shown positioned with the balloon  114 . Although a plurality of markers  142  are shown, it is contemplated that there may be only one or more fiducial markers  142 . It is contemplated that one or more fiducial markers  142  may be positioned anywhere with the balloon  114 , the shaft  112 , or the lumen  116 , including a lumen tip with ports. A fiducial marker  142 A is shown positioned at the end of the shaft  112 . The fiducial markers  142 ,  142 A may be made of a tungsten material, which may be detected by an MRI or CT scan. Other materials that may be visible on an MRI or CT scan are also contemplated, such as barium sulfate. Fiducial markers in powder or liquid form are contemplated. Other combinations and locations of markers  142 ,  142 A are contemplated. 
         [0086]    A first motion detecting sensor  143  is shown positioned with the balloon  114 . The motion detecting sensor  143  allows the treating physician to determine the movement of the any of the radiation detecting sensors  140 ,  140 A,  140 B,  140 C, fiducial markers  142 ,  142 A, balloon shaft  112 , lumen  116 , or the balloon  114  and the surrounding area, such as the part of the rectal wall near the prostate. One or more motion detecting sensors  143  may be positioned at any location with the balloon, the shaft, or the lumen. A second motion detecting sensor  143 A is shown placed at a different location with the surface the balloon. The motion detecting sensors  143 ,  143 A may be selected from any of the available sensors that enable the user to detect motion. 
         [0087]      FIG. 10  is a side view of a rectal balloon apparatus  120  having a balloon  124  with the gas pressure relieving activity of the rectal gas release lumen  126  integrated with the shaft  122 . The shaft  122  extends to an exterior of the balloon  124 , and has an opening  128  outside of the balloon  124 . A one-way valve means  130  may be formed within the shaft  122 . The one-way valve means  130  allows rectal gas to pass from the exterior of the balloon  124 , into the opening  128 , and through the one-way valve means  130  into the shaft  122 . The one-way valve means  130  prevents fluid or rectal gas from escaping through opening  128  from the interior of the shaft  122  when closed, but when open, the one-way valve means  130  operates to allow bodily gas to escape through the interior of the shaft  122  when the balloon  124  is installed in the rectum. Air or other fluid may be introduced into the balloon  124  so as to inflate the balloon  124 , while at the same time, closing the one-way valve means  130 , thus introducing fluid only to the balloon and not to the patient, and thereafter opened again. It is also contemplated that there may be no one-way valve means, and gas freely escapes via a completely separate air passageway throughout the treatment period. A flexible lumen tip with ports, like tip  156  in  FIG. 12 , may be positioned over opening  128 . The tip shown is closed, and the ports are adjacent thereto, but still distal to the balloon structure. The flexible tip or cap with ports may provide for patient comfort when the shaft  122  is inserted into the rectum, and the closed tip prevents or minimizes bodily material from entering the shaft  122 . Radiation detecting sensors  140 ,  140 A,  140 B,  140 C, fiducial markers  142 ,  142 A, and motion detecting sensors  143 ,  143 A may be positioned with the shaft  122  and/or the balloon  124  of  FIG. 10  as shown in  FIG. 9 . A sensor and/or fiducial marker may be positioned with a flexible tip with ports positioned over first opening  118  of lumen  116 . 
         [0088]      FIG. 11  shows a balloon  154  positioned with shaft  162  having a fluid passageway for inflating and deflating the balloon  154 , and the lumen  152  (best shown in  FIG. 12 ) for allowing gas pressure to escape from beyond the end of the balloon. The shaft  162  has ports in the area of the balloon for inflation and deflation, such as previously described. A flexible tip or closed cap  156  is positioned on the end of the lumen  152 . Rectal gas may enter the port  168  adjacent the cap  156 , and flow through the lumen  152 , escaping through the lumen port  150  on the splitting device  158 . One or more lumen tip ports  168  are contemplated. As shown in greater detail in  FIG. 13 , the splitting means  158  splits the lumen  152  from the fluid passageway of the shaft  162 . Returning to  FIG. 11 , anal dilator or collar  164  may be constructed of a hard material and locked over the shaft  162 . The collar  164  may have a hinge and a locking mechanism. Valve assembly  170  includes a control knob  172 . Turning the control knob  172  serves to close the valve assembly  170  so as to selectively allow the fluid to pass into the shaft  162 . A port  174  allows the valve assembly to be connected to a supply of the fluid. 
         [0089]    Turning to  FIG. 12 , radiation detecting sensors  140 ,  140 A,  140 B,  140 C, fiducial markers  142 ,  142 A, and motion detecting sensors  143 ,  143 A may be positioned with the shaft  162  and/or the balloon  154  similarly as shown in  FIG. 9 . A sensor and/or fiducial marker may be positioned with flexible lumen tip  156 . 
         [0090]    In  FIG. 13 , the lumen port  150  on the splitting device  158  may have a lip formation  182  for placement of a lumen port cap  180 . A luer lock formation or device is contemplated. It is contemplated that the cap  180  may be threadingly attached with the lumen port  150 . Other attachment means as are known in the art are contemplated. The cap advantageously prevents fluid from escaping the lumen  152 . 
         [0091]    A retrospective study was performed comparing to quantify the effects an ERB with a passive gas release conduit had on the incidence of rectal gas (Wooten 2012). Fifteen patients who were treated with a standard ERB and with a gas-release ERB (both from RadiaDyne) were selected and location and cross-sectional area of gas pockets and the fraction of time they occurred on lateral kilovoltage (kV) images were analyzed. Gas locations were classified as trapped between the ERB and anterior rectal wall, between the ERB and posterior rectal wall, or superior to the ERB, e.g towards the sigmoidal colon. The results, shown in  FIGS. 14A  and B show that the gas-release ERB significantly decreased the number of fractions in which gas was present, primarily by decreasing the incidence of gas trapped between the rectal balloon and the anterior rectal wall. Therefore, the study recommended that gas-release ERBs be used in patients undergoing radiation therapy for prostate cancer. 
         [0092]    Another study by Su found that compared to non-gas release balloons, gas release balloon reduced the magnitude of intrafractional prostate motion in both AP and SI directions. Thus, it allowed smaller treatment margins (Su 2012). 
         [0093]    The prevalence of gas found in the anterior region is consistent with previous findings and knowing that gas is most likely to be trapped in the anterior region is important because gas trapped there will not only displace the prostate, but also push the anterior rectal wall into the treatment field. This could potentially alter the prostate and rectal dose distribution and possibly the treatment outcome. 
         [0094]    In X-ray conformal or intensity-modulated radiation therapy, such a change in dose distribution would likely be small, and the negative effects of gas would stem mostly from organ displacement. However, in proton radiation therapy, gas in the treatment field can escalate dose to normal tissue to an unacceptably high level because of the extreme sensitivity of protons to the medium they travel through. A proton beam&#39;s range, and thus energy deposition, is extremely sensitive to the density of the medium through which the beam passes. Gas in the posterior and sigmoid regions can also displace the prostate, but this occurrence was not common when using either model of ERB in our analysis. 
         [0095]    The cross-sectional areas of gas pockets did not change significantly with respect to ERB model used demonstrating that, although gas occurs less often with the gas-release balloon, the severity of the gas is not decreased by it. A possible explanation for this result could be hasty gas-release ERB insertion that does not allow time for gas to escape through the conduit before being trapped when the balloon is inflated. 
         [0096]    If this is the case, the gas-release ERB could be used to better advantage by slow, careful insertion, giving the gas time to escape during all points of the insertion. Thus, inflation would not begin until the technician was reasonably sure that sufficient time was allowed for all gas to escape. Alternatively, additional gas releasing lumens can be glued to the exterior of the balloon, especially on the anterior side which sits adjacent the prostate, with holes there along to allow anterior gas pockets to escape. 
         [0097]    This shown in  FIG. 15 , a cross sectioned half of a gas release balloon having an exterior mounted gas release lumen. The balloon is made of bottom layer  1501  welded  1503  to top layer  1501  around the edges. If desired, this balloon can be shaped as described above, but such details are omitted from this figure for the sake of clarity. An optional central lumen is bifurcated at this point, providing a gas release passageway  1507 , as well as a balloon filling passageway  1509  that allows air to enter the balloon. Exterior gas release lumen  1511  is mounted to the outer layer of the balloon, e.g., by gluing or other welding process, and that lumen  1511  has openings  1513  along its length for allowing the escape of gas pockets trapped alongside the balloon. The posterior of the balloon can also be equipped with a similar lumen  1515 , but this is optional, as gas on this side of the balloon may present less of a problem due to the distance from the prostate. Central lumen  1507 / 1509  is optional in this embodiment, although shown herein, because the exterior lumen can serve the insertion function and can be provided with closed distal tip and ports. 
         [0098]    An important advantage of passive gas release over catheterization is that it continues to work during patient treatment. Although existing rectal gas may be removed by a catheter at the beginning of treatment, gas may continue to build up during the course of the treatment, and this occurance has been documented. The passive gas release balloon described herein alleviates build of gas upstream of the balloon, and if provided with an exterior gas release passageway mounted on an exterior surface of the balloon, even gas trapped alongside the balloon can be assured of release. 
         [0099]    The foregoing disclosure and description of the invention are illustrative and explanatory thereof, and various changes in the details of the illustrated apparatus and system, and the construction and method of operation may be made without departing from the spirit of the invention. 
         [0100]    The following are incorporated by reference herein in their entireties for all purposes. 
         [0101]    Wooten et al., Effectiveness of a novel gas-release endorectal balloon in the removal of rectal gas for prostate proton radiation therapy J. APPL. CLIN. MED. PHYS. 13(5): 190-197 (2012). 
         [0102]    Su, et al., Abstract 3192 Reduction of Prostate Intrafraction Motion using Gas-release Rectal Balloons, I. J. Radiation Oncology*Biology*Physics 81(2) (S. 2011). 
         [0103]    Su et al., Reduction of prostate intrafraction motion using gas-release rectal balloons, 5869 Med. Phys. 39 (10): 5869 (2012). 
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