seen in CO within FHR & VHR subgroups when compared by treatment type. UVA for the entire group of patients treated with IGART (n5130) revealed the following correlations to BC: pre-tx PSA continuous (p5.02), pre-tx PSA categorical (p5.048), & nadir (p !0.001), none of which were no longer significant on MVA. HDR-B exhibited significant findings only for nadir (p !0.001). CCI did not impact BC rates. Conclusions: Excellent clinical outcomes were observed for HR prostate cancer patients regardless of treatment type; however, HDR-B resulted in superior benefit in BC rates. Despite significant differences in CO for VHR & FHR patients, respectively, treatment type was not associated with differences in clinical or biochemical endpoints for these subgroups. PSOR07 Presentation Time: 8:30 AM Salvage Low-Dose-Rate Brachytherapy with Androgen Deprivation Therapy for Locally- Recurrent Prostate Cancer Cole R. Kreofsky, MD 1 , William W. Wong, MD 2 , Steven J. Buskirk, MD 3 , Lance A. Mynderse, MD 4 , Steven E. Schild, MD 2 , Chistopher L. Deufel, PhD 1 , Torrence M. Wilson, MD 4 , Brian J. Davis, MD, PhD 1 . 1 Department of Radiation Oncology, Mayo Clinic, Rochester, MN, USA; 2 Department of Radiation Oncology, Mayo Clinic, Scottsdale, AZ, USA; 3 Department of Radiation Oncology, Mayo Clinic, Jacksonville, FL, USA; 4 Department of Urology, Mayo Clinic, Rochester, MN, USA. Purpose: Local recurrences after prior external beam radiotherapy (EBRT) for localized prostate cancer are often treated with androgen deprivation therapy (ADT). For select patients, local therapy options (salvage prostatectomy, cryotherapy or brachytherapy (BT)) may be offered with curative intent. We report our institutional experience using salvage low- dose-rate brachytherapy (LDR-BT) and ADT in the treatment of local prostate cancer recurrence after prior EBRT. Methods: Twenty-two patients underwent salvage LDR-BT between 1999 and 2015; 21 of whom had follow-up information available. All patients had received previous EBRT, had a biopsy-proven prostatic recurrence, and a negative metastatic work up that included at least a CT-pelvis and a bone scan. Median prescription dose was 120 Gy for I-125 (range: 114-126 Gy), and of the 8 pts treated with Pd-103, prescribed dose was 103.5 Gy and 112.5 Gy to 4 patients each. Median D90 doses were 128.3 Gy (range: 113.5-151.9 Gy) and 119.4 Gy (range: 67.2-175.5 Gy) for I-125 and Pd-103, respectively. Urinary function was assessed with the AUA IPSS index. Genitourinary (GU) and gastrointestinal (GI) toxicity were graded using CTCAE v4.0. Biochemical failure was defined using the Phoenix definition (nadirþ2ng/dl). Survival estimates were performed using the Kaplan-Meier method. Results: Median patient age at time of LDR-BT was 71 yrs [range: 65-87 yrs]. Median interval between primary EBRT and salvage LDR-BT was 6.8 yrs [range: 2.4-13.5 yrs]. Median time between biopsy-confirmation of recurrent disease and LDR-BT was 6.2 months (range: 2.1-60.3 mos). Gleason scores at recurrence were: GS56 (32%), GS57 (36%), and GS$8 (32%). All pts received at least 2 months of neoadjuvant ADT prior to salvage BT (median 4 months); 8 patients (36%) received adjuvant ADT after salvage-BT (median 6 mos). Median follow up was 6.0 yrs. [range: 2.2-16.3 yrs]. Six patients (28.5%) experienced biochemical failure, 4 of whom went on to develop distant metastases. 2- and 5-yr biochemical control rates were 86% and 68%, respectively (there were no biochemical failures after 5 years). There were no documented local failures. Median overall survival was 11.7 yrs; and the 5- and 10-yr survival rates were 77% and 59%, respectively. Median baseline IPSS was 6 (range: 0-13), which rose to a median post-BT IPSS maximum of 16 (range: 5-30). Time to maximum IPSS score after BT ranged from 1-41 months (median5 6 mos). Maximum GU toxicity of grade 2 or grade $3 was seen in 48% of 38% of patients, respectively. Notably, 6 (29%) patients underwent urethral dilation due to stricture formation; 8 (38%) patients had urinary incontinence requiring pads; and 9 (43%) patients reported experiencing gross hematuria. Maximum grade 2 and grade 3 GI toxicities was seen in 4 (19%) and 2 (10%) patients, respectively. Conclusion: Salvage LDR-BT with concurrent ADT is an acceptable curative-intent treatment option for locally recurrent prostate cancer after prior EBRT for very select patients. There are increased rates of significant GU side effects compared to primary LDR-BT and patients should be counseled appropriately. PSOR08 Presentation Time: 8:35 AM MR-Guided High-Dose-Rate (HDR) Brachytherapy: Simultaneous Integrated Focal Boost to Intra- Prostatic GTV(s) Marco Carlone, PhD 1 , Alexandra Rink, PhD 1 , Akbar Beiki-Ardakani, PhD 1 , Anna Simeonov, MSc, MRT 1 , Bernadeth Lao, BSc 1 , Andrew Bayley, MD 1 , Gerald O’Leary, MD 2 , Cynthia M enard, MD 1 , Peter Chung, MD 1 , Alejandro Berlin, MD, MSc 1 . 1 Radiation Medicine Program, Princess Margaret Cancer Centre, Toronto, ON, Canada; 2 University Health Network, Toronto, ON, Canada. Purpose: To determine the feasibility and dosimetric impact to surrounding organs-at-risk (OAR) of delivering a simultaneous integrated boost to multiparametric MR-identified intra-prostatic lesions in the context of whole-gland MR-guided high-dose-rate (HDR) brachytherapy for prostate cancer (PCa). Materials and Methods: Consecutive patients enrolled in our institutionally approved MR-guided whole-gland (WG) HDR study were included. Planning imaging sequences (T2, axial reconstruction, 2mm thickness) acquired after MR-guided catheter insertion were used. GTV(s) were defined in previous diagnostic or pre-implant multiparametric MR. Cognitive or deformable registration (MORFEUS) were used to delineate the GTV(s) on the post catheters insertion planning MR. PTV margins were added to each GTV: 2mm craniocaudal and 1 mm in every other direction (PTVgtv). Remaining target volumes, organs at risk and catheter digitization were not modified. A new plan (Oncentra Brachy v4.3; IPSA algorithm, and manual modifications) of WGþGTV was obtained through iterative optimizations according to our departmental guidelines, with PTVgtv dose-escalation (V125 O 95%) added as planning objective. Corresponding WG plan previously delivered was used as additional guidance for limiting dose to surrounding OAR. Maximally achievable PTVgtv D95 was recorded. Final WGþGTV plan was subsequently compared to the actually delivered WG plan through the following parameters: prostate V100 and V150; and D0.5cc for rectum, urethra and bladder. Student’s t-test was used to compare means. Results: Ten patients with high-risk PCa treated with single 15Gy WG boost were included. All patients had identifiable lesion(s) (range 1-3) located at the base (3), apex (5) and mid gland (8) levels; and within the lateral peripheral zone (44%), anterior (31%), and medial peripheral zone (25%) regions. PTVgtv mean volume was 1.5cc (0.3-5.9cc), representing an average 5.1% (0.6-30.7%) of the prostatic volume. Median number of inserted catheters for WG plan was 17 (range 14-18). Mean volume of the prostate receiving the prescribed dose (V100) was 94.8% (93.4-95.6%) and 94.8% (93.6-95.4%) in the WG and WGþGTV plans respectively. Mean PTVgtv D95 significantly increased from 123.9% (102.4-152.3%) to 136.3% (128.3-153%), in WG and WGþGTV plans respectively (p50.007). The addition of GTV integrated focal boost, translated in non- significant percentage variations in D0.5cc of rectum (mean 1.81%; 0.02- 5.2%; p50.41), urethra (mean 1.6%; -4.1-5.6%; p50.58), and bladder (mean 0.67%; -8.19-12.46%; p50.9). In all cases, resultant WGþGTV plans remained within clinically acceptable dose-constrain criteria. Conclusions: Significant dose-escalation to intra-prostatic lesions by means of planned simultaneous integrated focal boost (125-150% of prescribed dose) is feasible in the context of MR-guided whole-gland (15Gy) HDR brachytherapy. Incremental dose to surrounding OAR is minimal when compared to delivered WG plans, and remained within our clinically acceptable dose-volume criteria. Prospective studies are S51 Abstracts / Brachytherapy 15 (2016) S21eS204