ENDORECTAL BALLOON WITH GAS LUMEN AND STOPPER

1 . A prostate immobilizing balloon, said balloon comprising:

i) an inflatable balloon having a proximal end and a distal end;

ii) 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;

iii) a first lumen communicating with an interior of said balloon, said first lumen having a closable valve;

iv) 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;

v) 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

vi) one or more fiducial markers on a surface thereof.

2 . The prostate immobilizing balloon of claim 1 , said locking member having a hemispherical distal surface for comfortably positioning adjacent an anus when in use.

3 . A method of treating prostate cancer by external beam radiation therapy (XRT), comprising:

a) inserting a prostate immobilizing balloon of claim 1 into a rectum of a patient with a cancerous prostate;

b) allowing rectal gas to exit the rectum via said one or more ports until no further exiting gas is evident;

c) inflating said balloon sufficiently to immobilize said prostate in said central seating area;

d) determining the position of said one or more fiducial markers and positioning said balloon such that said fiducial markers are in a desired position;

e) locking said locking member adjacent an anus;

f) treating said prostate with XRT; and

g) allowing rectal gas to exit the rectum via said one or more ports during said treating step.

4 . A method of treating prostate cancer by external beam radiation therapy (XRT), comprising:

a) inserting a prostate immobilizing balloon of claim 2 into a rectum of a patient with a cancerous prostate;

b) allowing rectal gas to exit the rectum via said one or more ports until no further exiting gas is evident;

c) inflating said balloon sufficiently to immobilize said prostate in said central seating area;

d) determining the position of said one or more fiducial markers and positioning said balloon such that said fiducial markers are in a desired position;

e) locking said locking member adjacent an anus;

f) treating said prostate with XRT; and

g) allowing rectal gas to exit the rectum via said one or more ports during said treating step.