The purpose of this study is to compare reproducibility of the device position and location of the prostate rectum interface between two immobilization devices for radiation therapy of prostate carcinoma.

The investigator assessed the device position and location of the interface between rectum and prostate weekly during the course of treatment. This information was obtained using a conebeam CT scan on the treatment couch prior to a regularly scheduled radiation treatment. The conebeam CT scan is a standard tool for monitoring patient position and radiation treatment accuracy. Prior to each radiation treatment, the patient was placed in a vaclock immobilization device, then aligned with room lasers to skin tattoos. On board portal imaging was then employed using the KvKv match technique to place isocenter as simulated. For intact prostate treatment, alignment was made to implanted gold fiducial markers. For post prostatectomy patients, the alignment was to pelvic bony anatomy. After patient alignment was complete, a conebeam CT scan was obtained. The position of the anterior rectal wall and the interface between prostate and rectum was compared to the position of these structures at the time of simulation. Measurement was taken in the midline of the prostate gland between its base and apex of the maximum deviation of the rectum prostate interface from its position at the time of simulation. For post prostatectomy patients, a measurement was taken of the maximum deviation from simulation of interface between the rectum and the prostate bed/bladder. These measurements were recorded weekly by the treating radiation oncologist on the Physician Data Sheet.

The difficulty of device insertion, positioning and inflation was recorded daily by the treating personnel based on a scale in the PIDS Daily Radiation Therapist Questionnaire, from 1(none) to 5(unable to insert). These results were summarized by the clinical study coordinators on the PIDS Radiation Therapist Summary.

Patient expression of discomfort during device placement was recorded daily by treating personnel based on a scale in the PIDS Daily Radiation Therapist Questionnaire, from 1(none) to 5(intolerable). These responses will be summarized by the clinical study coordinators on the PIDS Radiation Therapist Summary.

Inclusion Criteria:

• 18 years of age or older
• Clinically localized T1-3 N0-1 M0 adenocarcinoma of the prostate
• Planned definitive radiation therapy

Exclusion Criteria:

• Prior proctectomy
• Rectal surgery within one year
• Proctitis
• Rectal carcinoma
• Anal Stenosis
• History of inflammatory bowel disease
• Scleroderma
• Systemic sclerosis
• Refusal of treatment with immobilization device

up to nine weeks

Investigator interviews patient weekly during treatment with exam as needed to assess for adverse events.