The purpose of this research study is to learn more about the outcomes and early and late side effects of treating early stage prostate cancer with high dose rate brachytherapy.

Inclusion Criteria:

• Histologically or cytologically confirmed diagnosis of early stage prostate cancer.
• Must be considered either low-risk (T1-T2a, Gleason ≤ 6, PSA < 10 ng/mL) or favorable intermediate-risk (Gleason 3 +4 = 7, percentage of positive biopsy cores < 50%, no more than one NCCN intermediate risk factor).
• Prior androgen deprivation therapy is allowed and may have been initiated up to 6 months prior to the date of the HDR implant. The complete duration of androgen deprivation therapy can range from 4 months to 36 months provided it has been initiated no more than 6 months prior to the date of the HDR implant.
• At least 18 years of age.
• ECOG performance status ≤ 2
• Able to understand and willing to sign an IRB approved written informed consent document (or that of legally authorized representative, if applicable).

Exclusion Criteria:

• Prior radiation therapy to the prostate or lower pelvis encompassing the prostate.
• A history of other malignancy ≤ 5 years previous with the exception of basal cell or squamous cell carcinoma of the skin which were treated with local resection only.
• Currently receiving any other investigational agents.
• Uncontrolled intercurrent illness including, but not limited to, ongoing or active infection, symptomatic congestive heart failure, unstable angina pectoris, or cardiac arrhythmia.
• Unable to undergo general, spinal or local anesthesia.
• Prior TURP with a sufficiently large defect that would compromise the integrity of the implant per clinician's assessment.