Background: The ASCO/CCO guidelines recommend brachytherapy boost for all eligible intermediate- or high-risk localized prostate cancer patients. We present efficacy, survival and late toxicity outcomes in patients treated on a prospective, single institutional protocol of MRI dose painted HDR brachytherapy boost (HDR-BT) followed by pelvic stereotactic body radiotherapy (SBRT) and androgen deprivation therapy (ADT). Methods: A phase I/II study was performed where intermediate (IR) or high-risk (HR) prostate cancer patients received HDR-BT 15Gy x 1 to the prostate and up to 22.5Gy to the MRI nodule and followed by gantry-based SBRT 25Gy in 5 weekly fractions delivered to pelvis, seminal vesicles and prostate. ADT was used for 6-18 months. CTCAEv3 was used to assess toxicities and was captured q6months x 5 years. Biochemical failure (BF; nadir + 2 definition), nadir PSA, proportion of patients with PSA < 0.4 ng/ml at 4 years (4yPSARR), incidence of salvage therapy, cause specific survival and overall survival were calculated. Day 0 was HDR-BT date for all time-to-event analyses. Results: Thirty-two patients (NCCN 3% favorable IR, 47% unfavorable IR and 50% HR) completed the planned treatment with a median follow-up of 50 months; 31 of these had an MRI nodule. Four patients had BF with actuarial 4-year BF rate of 11.5%; 3 of these received salvage ADT. Median nPSA was 0.02 ng/ml; 4yPSARR was 68.8%. One patient died (of prostate cancer) at 45 months. For late toxicities, grade 1, 2 and 3+ GU and GI toxicities were: 40.6%, 37.5%, 3% and 28.1%, 0%, 0%, respectively. Conclusions: This novel treatment protocol incorporating MRI-dose painted HDR brachytherapy boost and SBRT pelvic radiation for intermediate- and high-risk prostate cancer in combination with ADT is feasible, effective and well tolerated. Clinical trial information: 12345678.