for penetration with or without sexual aids. Eighty-six men were identified as being potent at the initiation of therapy. All patients were treated to 35- 36.25 Gy in 5 fractions delivered with robotic radiosurgery. Patients who received hormonal therapy were excluded from this study. Sexual function was assessed with the Sexual Health Inventory for Men (SHIM), Expanded Prostate Index Composite (EPIC), and Utilization of Sexual Medication/ Device questionnaires at baseline and at 6, 12, 18, and 24 months. Sexual aid utilization was documented at each visit. Results: Mean age at treatment was 70. Minimum follow-up was 24 months. The median baseline SHIM was 21. Forty percent of patients utilized sexual aids prior to treatment. Potency rates declined following treatment: 100% (baseline); 68% (6 months); 69% (12 months); 66% (24 months). For patients < 70 years old, 72% maintained potency at two years. Overall sexual aid utilization increased to 65% at 24 months. Median EPIC sexual scores showed a slow decline over the first two years following treatment: 79 (baseline); 79 (6 months); 71 (12 months); 71 (24 months). However, median sexual bother scores were unchanged: 75 (baseline); 75 (6 months); 75 (12 months); 75 (24 months). Only 7 patients (9%) experience complete loss of erections at 24 months post treatment. Conclusions: Men with preserved potency undergoing SBRT monotherapy for prostate cancer have sexual outcomes within the first 24 months after treatment comparable to those reported for alternative radiation modalities. Longer follow-up is required to confirm the durability of these findings. Author Disclosure: O. Obayomi-Davies: None. T.K. Kole: None. L.N. Chen: None. S. Uhm: None. J. Kim: None. B.T. Collins: G. Consultant; Accuray. S. Suy: None. J.H. Lynch: None. A. Dritschilo: None. S.P. Collins: G. Consultant; Accuray. 179 Prospective Long-term Patient-Reported Quality of Life After Proton Therapy for Prostate Cancer A.K. Lee, S. Choi, Q.N. Nguyen, T.J. Pugh, U. Mahmood, B. Mathai, J. Johnson, X. Zhu, T. Ly, and M.F. Munsell; University of Texas MD Anderson Cancer Center, Houston, TX Purpose/Objective(s): To prospectively evaluate patient-reported quality of life (QOL) after proton therapy for prostate cancer (PCa). Materials/Methods: PCa patients treated with proton therapy (PT) were enrolled on a prospective QOL protocol and asked to complete the Expanded Prostate Cancer Index Composite (EPIC) before PT and at 3-6 months intervals following PT. Men received 75.6 Gray Equivalents (GyE) at 1.8 GyE/fraction (n Z 95) or 76-78 GyE at 2 GyE/fraction (n Z 147). Men with baseline- and 4 year post-PT surveys were included in the analysis (n Z 242). Statistically significant changes in mean scores from baseline were determined using a t-test, and clinically significant changes were based on changes > 0.5 * standard deviation of baseline. The cumulative incidence of acute and late toxicities as per modified-RTOG scale was determined by Gooley. Results: All men were followed for at least 4 years. Median age at diagnosis was 65.5 years (range, 46-82), median pre-treatment PSA was 4.5 ng/mL (0.1-18.6), 44.6% received hormone therapy (median duration 6 months), Gleason sum 6 was seen in 40.9% and Gleason sum 7 in 59.1%. Most men (61.2%) were intermediate risk and 38.8% were low risk. Statistically significant changes from baseline at 4 years post-PT were seen in multiple sexual, urinary, bowel and hormonal/vitality domains. However, clinically significant changes were not seen in any domains except for bowel scores within 3.5 years. At 4 years, no clinically significant changes were reported in any domain. At 4-years, 96.3% of men reported using 0-1 urinary pad (93.4% used 0). At least “moderate” problems with urinary function, bowel habits, bloody stools and sexual function were reported in only 3.7%, 3.8%, 0.8%, and 37.6% of men, respectively. The cumulative incidence of acute grade 2 urinary side effects (mostly a blockers) was 51.2% and acute grade 2 rectal was 8.7%. No acute grade 3 or higher toxicities. The cumulative incidence of late grade 2 urinary and rectal side effects were 17.4% and 12.4%. One patient had a late grade 3 rectal toxicity. The prevalence of late grade 2 GU/GI side effects at last contact was < 2%. The cumulative incidence of PSA failure for all patients was 6.5%. At 4-years, 93.4% of men were satisfied or extremely satisfied with their treatment. Conclusions: In this long-term prospective study, proton therapy resulted in statistically significant but not clinically significant changes in patient QOL at 4 years. Overall, the toxicity and impact on quality of life were low. Patient satisfaction rates were high. Author Disclosure: A.K. Lee: None. S. Choi: None. Q.N. Nguyen: None. T.J. Pugh: None. U. Mahmood: None. B. Mathai: None. J. Johnson: None. X. Zhu: None. T. Ly: None. M.F. Munsell: None. 180 Clinical and Treatment Factors Associated With Vaginal Stenosis After Definitive Chemoradiation for Anal Cancer K.L. Mirabeau-Beale, 1 T.S. Hong, 2 M. Ancukiewicz, 2 D.P. Ryan, 2 L.S. Blaszkowsky, 2 L.C. Drapek, 2 J.C.J. Cusack, 2 L.A. Kachnic, 3 and J.Y. Wo 2 ; 1 Harvard Radiation Oncology Program, Boston, MA, 2 Massachusetts General Hospital, Boston, MA, 3 Boston Medical Center/ Boston University, Boston, MA Purpose/Objective(s): Although VS (vaginal shortening and/or decreased width) is a known long-term toxicity after pelvic radiation therapy (RT) for gynecologic cancer, few studies have evaluated its incidence after defini- tive chemoRT for anal cancer. We retrospectively reviewed the clinical and treatment characteristics of women treated for anal cancer to identify factors associated with VS. Materials/Methods: Ninety-six consecutive women who received defini- tive chemoRT for anal squamous cell carcinoma between 2005 and 2012 comprised the study cohort. NCI CTCAE v. 4 was used to score for VS based on the medical record description of dyspareunia, vaginal dryness or difficult pelvic exam. Other clinical factors examined included age, race, body mass index (BMI), menopausal status, smoking, tumor size/lymph node status (AJCC 7th edition), immunocompromised status, and treat- ment with abdominoperineal resection (APR). The exact Wilcoxon-Mann- Whitney and Jonckheere Terpstra tests were used to assess VS risk factors. Results: Median age was 60.4 years (range, 19-97). Patient characteristics included: 26% non-White; 14% pre-menopausal; 9% immunocompro- mised; and 51% with current or prior tobacco use. Stage distribution included 17% T1, 39.5 % T2, 26.5% T3, and 17% T4 tumors; 43% were node positive. Ninety-eight percent received dose-painted IMRT to a median primary tumor dose of 50.4 Gy (range, 41.4 Gy-60 Gy). Chemotherapy included: 83% concurrent mitomycin-C and 5-fluorouracil Oral Scientific Abstract 179; Table Mean EPIC scores 0-100 (std deviation, * denotes clinically significant change) EPIC domain Baseline 1-Year 2-Year 3-Year 4-Year Change from baseline to 4-Year Statistically significant change from baseline (P value) Clinically significant change from baseline (P value) Urinary summary 90 (10.1) 88.9 89.8 89.4 89.7 0.3 .935 .99 Urinary function 96 (8.8) 93.5 93.8 93.4 93.5 2.5 .002 .99 Urinary bother 85.4 (13.2) 85.4 87 86.5 86.8 1.6 .089 .99 Bowel summary 94.8 (6.1) 87.5* 89* 90.7* 91.4 3.3 < .001 .35 Bowel function 93.8 (7.1) 88.2* 89.3* 90.9* 91.3 2.4 < .001 .95 Bowel bother 95.7 (6.7) 87* 88.7* 90.4* 91.4 4.4 < .001 .99 Sexual summary 54.5 (27.4) 51.3 49.2 48.8 46.8 7.5 < .001 .99 Sexual function 50.9 (27.5) 48.3 45.9 45.3 42.7 8.0 < .001 .99 Sexual bother 62.5 (33.2) 59.4 57.5 57.8 57 5.4 < .001 .99 International Journal of Radiation Oncology  Biology  Physics S74