This prospective, 2-arm clinical trial aims to evaluate the use of rectal spacers in patients with localized prostate cancer scheduled for Proton Beam Therapy (PBT). Up to 50 subjects will be enrolled in this study.

Study visits will include screening, spacer placement, treatment planning, end-of-treatment assessment, and follow-up visits at 1, 3, and 6 months.

Inclusion Criteria

1. Subjects greater than 18 years old with prostate cancer
2. Subjects must have histologically confirmed adenocarcinoma of the prostate with biopsy taken within 12 months and must be planned to undergo proton beam therapy with rectal spacer
3. Subjects must have clinical stage T1-T3 with no posterior extra capsular extension of the prostate cancer
4. PSA less than or equal to 20 ng/mL
5. Gleason Score less than or equal to 7
6. Capacity to comprehend and readiness to sign a written informed consent form

Exclusion Criteria

1. Planned Pelvic lymph node radiotherapy.
2. Metastatic disease.
3. Prior local prostate cancer therapy
4. Active Inflammatory bowel disease requiring treatment with steroids.
5. Prior radical prostatectomy.
6. Active urinary tract infection.
7. Acute or chronic inflammation or infection of the prostate.