ranged between 5 and 179 ng/ml (mean: 37). Gleason score (GS) was distributed as follows: 6 in 8, 7 in 49, and 8 or higher in 46 cases. NA-HT (4-15 months, mean: 7) were given to all cases. Seventy-eight Gy in 39 fractions was prescribed to the prostate and seminal vesicles in 94 cases, while the doses were reduced to 70 or 74 Gy in 9 patients due to adverse factors such as anti-coagulant therapy. No adjuvant hormonal therapy was given to any patients. As a general rule, salvage HT was not initiated until the PSA value exceeded 4 ng/ml after the judgment of PSA failure or any clinical failures were found. Outcomes were also compared with those of 70 patients previously treated with 3D-CRT delivered 70 Gy. Results: Median follow-up period was 53 months (range: 21-70). Estimated biochemical relapse-free survival (bRFS) rate based on the Phoenix definition by the Kaplan-Meyer method was 69% (95% CI = 59-79) at 4 years. Among age, NA-HT duration, GS, iPSA and T-factor, only the iPSA and T-factor were significant independent factors for bRFS outcome in both univariate and mul- tivariate analyses. 4-year bRFS rates for non-T3b cases and T3b cases were 76% (95% CI = 64-87) and 53% (95% CI = 59-79), respectively (p = 0.0033). 4-year bRFS rates for patients with PSA \=30 and PSA.30 were 79% (95% CI = 66-92) and 55% (95% CI = 40-70), respectively (p = 0.019). Only delivered dose was significantly different in patients’ backgrounds between 3D-CRT and IMRT. Mean ± SD of PSA values at salvage HT were 7.3 ± 6.1 and 8.2 ± 6.9 ng/ml, respectively (p = 0.46). Difference of the salvage hormonal therapy-free survival rate at 4 years in non-T3b cases between IMRT (85%) and 3D-CRT (69%) was marginally significant (p = 0.053), while those in cases with T3b disease, PSA \=30 and PSA.30 were not statistically significant (p = 0.42, 0.30 and 0.54, respectively). Estimated incidence of grade 2 or higher late rectal and urinary adverse events were 5.9% and 6.3% at 4 years, respectively. Conclusions: High dose localized irradiation to patients with T3-4N0M0 prostate cancer has been safely conducted and bRFS out- comes seem promising so far. Patients with non-T3b disease may receive significant benefit from high dose local IMRT combined with NAHT, although longer follow-up and additional study in prospective setting would be necessary to draw any conclusions. Author Disclosure: T. Mizowaki, Mitsumishi Heavy Industry, F. Consultant/Advisory Board; K. Takayama, Mitsubishi Heavy Industry, B. Research Grant; Y. Norihisa, None; S. Yano, None; T. Kamoto, None; E. Nakamura, None; T. Kamba, None; T. Inoue, None; O. Ogawa, None; M. Hiraoka, Mitsubishi Heavy Industry, F. Consultant/Advisory Board. 2385 Post-operative Image-guided Intensity-modulated Radiation Therapy for Prostate Cancer: Acute and Late Gastrointestinal and Genitourinary Toxicity A. Sandhu, S. K. Nath, B. S. Rose, D. R. Simpson, P. D. Nobiensky, J. Z. Wang, F. Millard, J. K. Parsons, C. J. Kane, A. J. Mundt University of California San Diego, La Jolla, CA Purpose/Objective(s): Intensity-modulated radiation therapy (IMRT) has an emerging role in the management of post-prostatec- tomy patients with prostate cancer. To account for organ motion, we have devised a unique system of prostate-bed localization using daily image-guidance to existing surgical clips. We report here on the acute and late gastrointestinal (GI) and genitourinary (GU) toxicity associated with this technique. Materials/Methods: Fifty patients (pts) were treated between 2005 and 2008 with IMRT following radical prostatectomy. Median pt age was 63 (range, 52-77). Pathologic stages were T1c (2%), T2a (4%), T2b (6%), T2c (30%), T3a (26%), T3b (28%), T4 (2%) and unavailable (2%). Median Gleason score was 7 (range 6-9). Adjuvant therapy was given to 13 pts (26%), and salvage therapy to 37 pts (74%). The median radiation dose was 68 Gy (range, 62-68) given in 34 fractions (range, 31-37). The planning target volume was generated with an 8-10 mm margin around the prostate bed, except posteriorly where it was reduced to 5 mm. Prostate bed localization was performed daily by taking orthogonal kilovoltage (kV) images (90%) or cone-beam CT (CBCT) (10%). Patients were repositioned according to the alignment of surgical clips between the kV or CBCT images and the planning digitally recon- structed radiographs (DRRs). Follow-up occurred every 3-6 months. Toxicity was graded according the Common Toxicity Criteria version 3.0. Acute toxicities were defined as events occurring during treatment or #90 days from the completion of treatment. Late toxicities were new or persisting events occurring .90 days from treatment completion. Results: Median follow-up for all 50 pts was 24 months (range, 13-38). Grade 1 and grade 2 acute GI toxicities occurred in 29 (58%) and 7 (14%) pts. Grade 1 and 2 acute GU toxicity occurred in 26 (52%) and 9 (18%) pts. No grade 3 or higher acute GI or GU toxicity was observed. In addition, no pts required treatment interruptions. Grade 1 and 2 late GI toxicity occurred in 4 (8%) and 1 (2%) pts, respectively. No grade 3 or higher late GI toxicity was observed. Grade 1, 2, and 3 late GU toxicity occurred in 4 (10%), 8 (16%) and 1 (2%) pts. The single grade 3 GU toxicity was bleeding requiring coagulation in a pt on coumadin. The 2- year cumulative incidence of grade 2 or higher late GI toxicity was 2% (95% confidence interval [C.I.], 0.3-14). The 2-year cu- mulative incidence of grade 2 or higher and grade 3 or higher late GU toxicity was 16% (95% C.I., 9-30) and 2% (95% C.I., 0.3-14), respectively. No grade 4 events were observed. Conclusions: Image-guided IMRT in the post-prostatectomy setting can reduce the incidence of acute and late GI/GU toxicity. More importantly, no severe high-grade acute or late GI/GU toxicities were observed. Author Disclosure: A. Sandhu, None; S.K. Nath, None; B.S. Rose, None; D.R. Simpson, None; P.D. Nobiensky, None; J.Z. Wang, None; F. Millard, None; J.K. Parsons, None; C.J. Kane, None; A.J. Mundt, None. 2386 Factors Influencing PSA Kinetics after External Beam Radiotherapy for Intermediate Risk Prostate Cancer D. Taussky 1 , G. Delouya 1 , G. Kaufman 2 , J. Bahary 1 , T. Nguyen 1 , P. Despre ´s 1 1 Hospital Notre-Dame CHUM, Montreal, QC, Canada, 2 Centre de Recherche, CHU Sainte-Justine, Montreal, QC, Canada Purpose/Objective(s): To study the influence of various parameters on PSA (Prostate-Specific Antigen) kinetics and especially ex- ponential PSA decay after external-beam radiotherapy (EBRT) in a randomized prospective study for intermediate risk prostate cancer. Materials/Methods: We analyzed 67 patients from our institution with intermediate risk prostate cancer (Gleason 6 + PSA 10-20 or Gleason 7 + PSA \10). Patients were randomized between either 70.2 Gy (1.8 Gy per day) or 79.2 Gy. All patients had a follow up of at least 6 PSA measurements post-EBRT. Patients were divided into two groups based on whether the behavior of their PSA S354 I. J. Radiation Oncology d Biology d Physics Volume 75, Number 3, Supplement, 2009