Stereotactic Ablative Radiotherapy (SABR) for Low Risk Prostate Cancer With Injectable Rectal Spacer

Inclusion Criteria:

* All patients must be willing and capable to provide informed consent to participate in the protocol.
* Eligible patients must have appropriate staging studies identifying them as AJCC stage T1 (a, b, or c) or T2a or T2b adenocarcinoma of the prostate gland. The patient should not have direct evidence of regional or distant metastases after appropriate staging studies. Histologic confirmation of cancer will be required by biopsy performed within 180 days of registration.
* The patient's Zubrod performance status must be 0-2.
* The Gleason score should be less than or equal to 6 or 3+4 if \< 50% of a 12 core biopsy was involved.
* The serum PSA should be less than or equal to 10 ng/ml.
* Study entry PSA must not be obtained during the following time frames: 10 day period following prostate biopsy; following initiation of ADT; within 30 days after discontinuation of finasteride; or within 90 days after discontinuation of dutasteride.
* Age ≥ 18 years.
* Patients may have used prior hormonal therapy, but it should be limited to no more than 9 months of therapy prior to enrollment.
* The ultrasound, or CT based volume estimation of the patient's prostate gland should be ≤ 60 grams.

Exclusion Criteria:

* Subjects who have had previous pelvic radiotherapy or have had chemotherapy or surgery for prostate cancer.
* Subjects who have plans to receive other concomitant or post treatment adjuvant antineoplastic therapy while on this protocol including surgery, cryotherapy, conventionally fractionated radiotherapy, hormonal therapy, or chemotherapy given as part of the treatment of prostate cancer.
* Subjects who have undergone previous transurethral resection of the prostate (TURP) or cryotherapy to the prostate. Subjects who have significant urinary obstructive symptoms; AUA score must be ≤15 (alpha blockers allowed).
* Subjects who have a history of significant psychiatric illness.
* Men of reproductive potential who do not agree that they or their partner will use an effective contraceptive method such as condom/diaphragm and spermacidal foam, intrauterine device (IUD), or prescription birth control pills.
* Prior invasive malignancy (except non-melanomatous skin cancer) unless disease free for a minimum of 3 years (e.g., carcinoma in situ of the breast, oral cavity, or cervix are all permissible).
* Severe, active co-morbidity, defined as follows:

  * Unstable angina and/or congestive heart failure requiring hospitalization within the last 6 months.
  * Transmural myocardial infarction within the last 6 months.
  * Acute bacterial or fungal infection requiring intravenous antibiotics at the time of registration.
  * Chronic Obstructive Pulmonary Disease exacerbation or other respiratory illness requiring hospitalization or precluding study therapy within 30 days before registration.
  * Hepatic insufficiency resulting in clinical jaundice and/or coagulation defects; note, however, that laboratory tests for liver function and coagulation parameters are not required for entry into this protocol.
  * Acquired Immune Deficiency Syndrome (AIDS) based upon current CDC definition; note, however, that HIV testing is not required for entry into this protocol. The need to exclude patients with AIDS from this protocol is necessary because the treatments involved in this protocol may be significantly immunosuppressive. Protocol-specific requirements may also exclude immuno-compromised patients.
  * Patients with history of inflammatory colitis (including Crohn's Disease and Ulcerative colitis) are not eligible.
* Subjects with a known allergy to polyethylene glycol hydrogel (spacer material) or contraindication to spacer products (Duraseal or SpaceOAR).
* Subjects with evidence of extraprostatic extension (T3a) or seminal vesicle involvement (T3b) on clinical evaluation.