Assessing the Potential for Reduced Toxicity Using Focal Brachytherapy in Early Stage, Low Volume Prostate Cancer

Inclusion Criteria: * Men ≥ 21 years of age with a life expectancy estimated to be \> 10-years. * Diagnosis of adenocarcinoma of the prostate confirmed by MSKCC or participating site pathology review. * Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1 * Prostate cancer clinical stage T1c-T2a * PSA \< 10ng/mL (this will be the PSA level prompting the prostate biopsy) * MRI evidence of one-sided disease performed within 3 months of registration * Prostate size \<60 cc at time of treatment- if the prostate is larger, hormonal therapy is allowed to achieve the required size Screening biopsy parameters: * Minimum of 10 biopsy cores * Gleason grade 7 in two cores or less, with no primary Gleason grade 4 or 5 in any cores * Unilateral cancer (only right-sided or left-sided, not bilateral) * No more than 50 % cancer in any one biopsy core * No more than 25 % of cores containing cancer * Repeat transrectal or transperineal prostate biopsy that must meet the following parameters: * Minimum of 12 biopsy cores * Unilateral cancer (only right-sided or left-sided, not bilateral) * Gleason grade 7 in two cores or less, with no primary Gleason grade 4 or 5 in any cores * No more than 50 % cancer in any one biopsy core * No more than 25 % of cores containing cancer Subject Exclusion Criteria: * Medically unfit for anesthesia * Evidence or suspicion of extracapsular extension on MRI * IPSS score \> 18 * Unable to receive MRI * Prior radiotherapy for the current disease