Was not meeting target enrollment; other treatment options precluded completing study

This phase II trial studies the effect of rectal spacer hydrogel before radiation therapy in reducing radiation dose to the rectum in patients with prostate cancer. Rectal spacer hydrogen is a soft gel material used to create a space between the rectum and prostate during radiation treatment. The rectal spacer gel is made up of 90% water and 10% polyethylene glycol and is injected as a liquid through a needle inserted between the rectum and prostate. It stays in place for about 3 months and is naturally absorbed into the body and removed through urine in about 6 months. By pushing the prostate further from the rectum with the hydrogel, it may help spare the rectum from receiving radiation during standard of care stereotactic body radiation therapy and brachytherapy treatment.

The purpose of this research study is to observe the effects of using an FDA-approved rectal spacer device known as the SpaceOAR Hydrogel, which is a soft gel material used to create a space between the rectum and prostate during radiation treatment. The rectal spacer gel is made up of 90% water and 10% polyethylene glycol and is injected as a liquid through a needle inserted between the rectum and prostate. It will stay in place for about 3 months and is naturally absorbed into the body and removed through urine in about 6 months. By pushing the prostate further from the rectum with the hydrogel, it will help spare the rectum from receiving radiation during the standard of care stereotactic body radiation treatment participant will be receiving, along with the brachytherapy treatment. The hydrogel rectal spacer has been shown to be very safe and effective at reducing radiation dose to the rectum during external radiation treatments, but has not been well-studied when using a combination of Stereotactic Body Radiation Therapy (SBRT) and brachytherapy. The goal of this research is to determine how effective the SpaceOAR hydrogel rectal spacer is at decreasing radiation side effects that can occur in the rectum, which can include discomfort or bleeding. The researchers also want to see how the use of this device affects the doctor's ability to perform the brachytherapy implant safely and effectively.

Inclusion Criteria:

• Histologically/biopsy confirmed adenocarcinoma of prostate within 1 year of registration
• Disease confined to the prostate. Prostate volume must be <150cc confirmed by pelvic CT (with or without contrast) or pelvic/prostate MRI (with or without contrast) +/- ultrasound, within 8 months of signing research consent
• Age >18
• Patients deemed medically suitable to undergo rectal spacer placement, external beam radiotherapy and brachytherapy at the discretion of the radiation oncologist, urologist, medical oncologist and/or internist.
• ECOG score of 0-2.
• One or more of the following risk factors for intermediate risk prostate cancer; T2b or T2c clinical stage, GS 7 (either 3+4 or 4+3), PSA 10-20.
• Ability to understand and the willingness to sign a written informed consent.
• PSA result within 6 months of simulation

Exclusion Criteria:

• Patients with disease not confined to the prostate based on imaging, biopsy, or clinical exam
• Patients with a prostate size > 100 cc based on computed tomography (CT), magnetic resonance imaging (MRI), or ultrasound measurements
• Patients who have undergone previous rectal, bowel, bladder, or prostate surgeries in the past
• Patients with previous treatments for their prostate cancer or that are currently receiving any other experimental therapies
• Patients who have undergone prior pelvic radiotherapy
• Patients with high risk prostate cancer that have any of the following risk factors; GS >= 8, PSA > 20, clinical or imaging stage T3a or higher
• Patients receiving antiandrogen therapy (ADT)
• Patients with any prior active or treated genitourinary malignancy

Sharing data is not planned unless specifically requested by another institution.