This is a prospective clinical trial examining the use of MRI to measure internal organ motion and any resulting changes in the target volume (shape and location) during a course of post-operative radiation therapy for prostate cancer. The goal is to better understand and characterize these physiologic variations so that they can be accounted for during the treatment planning process. The ultimate longer-term clinical goal here is to provide a form of adaptive radiation therapy in the future, such that if major changes are seen over an 8-week course of radiation therapy in our study. This may argue for hypofractionating those patients who are most likely to have major shifts over time.

PRIMARY OBJECTIVES:

I. To evaluate the use of MRI in delineating clinical target volumes, as well as endorectal balloon target immobilization in patients treated with radiation following radical prostatectomy.

SECONDARY OBJECTIVES:

II. Trends over time in CTV, bladder and rectum volumes and percent change from baseline at each time point. III. Frequency of events in which the CTV falls outside the PTV. IV. Proportion of the total CTV which falls outside the PTV at each event. V. Trends over time in dose-volume exposures for bladder and rectum.

OUTLINE: Patients undergo MRI and CT scan-based simulation for treatment planning with endorectal balloon target immobilization. The treatment target volumes and surrounding organs at risk are contoured, treatment plan developed and approved.

Patients then undergo 39 fractions of image-guided intensity-modulated radiotherapy over 8 weeks. Patients also undergo weekly MRI scans of the pelvis (in the planned treatment position) during radiotherapy.

Inclusion

• Completion of a radical prostatectomy for adenocarcinoma of the prostate
• Scheduled post-operative radiation therapy as part of the patient's treatment for prostate cancer
• Subjects are capable of giving informed consent

Exclusion

• The presence of grossly visualized or palpable disease recurrence
• Patients who are unable to undergo an MRI scan such as those with an implanted permanent pacemaker or ICD
• Patients with metastatic disease or an increasing PSA