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intermediate-risk patients. 2) Subgroup analysis with each risk factors (T classification, GS, PSA and % of positive core) and number or risk factors. Results The median follow-up was 74 months (range, 4 - 135 months). All patients received 74 Gy (RBE) in 37 fractions and 262 (44%) patients received N-ADT with the median duration of 7 months (range, 1 - 84 months). For all patients, 5- and 10- year FFBR were 91% and 82%, respectively. N-ADT did not improve FFBR (91% vs. 91%, P = 0.925) for all patients (Figure 1). On the subgroup analysis using each risk factors and number of risk factors, N-ADT did not improve FFBR with statistically significant differences. Conclusion PT provided excellent biochemical control for patients with intermediate-risk prostate cancer. In this study, N- ADT did not improve biochemical control of patients with intermediate-risk prostate cancer. EP-1572 Effect of patient positioning on organs at risk in postoperative radiotherapy for prostate cancer S. Sawayanagi 1 , H. Yamashita 1 , M. Ogita 1 , W. Takahashi 1 , K. Nakagawa 1 1 University of Tokyo, Radiology, Tokyo, Japan Purpose or Objective The aim of this study was to find the optimal patient positioning contributing to reduction of organs at risk (OARs) dose in adjuvant or salvage radiotherapy for prostate cancer after prostatectomy. Material and Methods 12 patients who received intensity-modulated radiation therapy (66 Gy in 33 fractions) as adjuvant or salvage therapy after prostatectomy were evaluated. All patients underwent CT scans with a full bladder and an empty rectum in both the prone (on a belly board) and supine positions. The target volumes and OARs (small intestine, rectum, femurs, bladder, and sigmoid) were delineated on each CT series. A prostate bed was contoured as the clinical target volume (CTV) using Radiation Therapy Oncology Group (RTOG) consensus guidelines. The CTV was extended by 7 mm in every direction except posterior with 5 mm extension to generate the planning target volume (PTV). The PTV+0.5 cm was defined as the region extended by 0.5 cm in every direction from the PTV. The PTV+1 cm, the PTV+2 cm, the PTV+3 cm, and the PTV+4 cm were also defined as in the case of the PTV+0.5 cm. We calculated the volumes of OARs overlapping with the PTV and the extended target volumes. The overlapping volumes in the prone and supine position were compared using the paired t-test. Results The overlapping volumes of small intestine were 2.1±3.6 cc (prone, mean±95% CI) vs 11.1±10.0 cc (supine, P=0.047) with the PTV, 3.7±5.9 cc (prone) vs 17.1±14.3 cc (supine, P=0.043) with the PTV+0.5 cm (equivalent dose of 49 Gy), 5.0±7.5 cc (prone) vs 24.2±18.7 cc (supine, P=0.033) with the PTV+1 cm (equivalent dose of 36 Gy), 7.9±9.5 cc (prone) vs 38.0±29.3 cc (supine, P=0.037) with the PTV+2 cm, 12.7±11.0 cc (prone) vs 51.6±39.5 cc (supine, P=0.041) with the PTV+3 cm, and 21.8±14.1 cc (prone) vs 67.0±48.4 cc (supine, P=0.049) with the PTV+4 cm respectively. The overlapping volumes of rectum were 11.7±2.5 cc (prone) vs 13.5±2.5 cc (supine, P=0.029) with the PTV, 26.3±4.4 cc (prone) vs 30.5±4.5 cc (supine, P=0.01) with the PTV+0.5 cm, 39.6±6.3 cc (prone) vs 45.9±6.2 cc (supine, P=0.01) with the PTV+1 cm respectively. The overlapping volume of bladder with the

PTV was 66.4±11.0 cc (prone) vs 82.5±13.1 cc (supine, P=0.045). On the other hand, the overlapping volumes of femurs in the supine position were significantly smaller than the ones in the prone position. None of body mass index (BMI), the interval between prostatectomy and the start of radiotherapy, and age was single predictive factor of the overlapping volumes. Conclusion The regions receiving high-dose radiation in small intestine, rectum, and bladder may be reduced in the prone position in adjuvant or salvage radiotherapy for prostate cancer after prostatectomy. EP-1573 Long term outcomes in 1121 Australian prostate cancer patients treated with definitive radiotherapy J. De Leon 1 , A. Kneebone 2 , V. Gebski 3 , S. Cross 3 , V. Do 4 , A. Hayden 3 , D. Ngo 5 , M. Sidhom 5 , S. Turner 3 1 Illawarra Cancer Care Centre, Radiation Oncology, Illawong, Australia 2 Northern Sydney Cancer Centre, Radiation Oncology, St Leonards, Australia 3 Crown Princess Mary Cancer Care Centre, Radiation Oncology, Westmead, Australia 4 Nepean Cancer Care Centre, Radiation Oncology, Nepean, Australia 5 Liverpool Cancer Care Centre, Radiation Oncology, Liverpool, Australia Purpose or Objective Optimal definitive treatment of prostate cancer is controversial, especially in high risk patients. We report the largest prospective cohort of Australian patients treated with radiotherapy for localised prostate cancer. Material and Methods One thousand, one hundred and twenty-one patients with prostate cancer were prospectively registered and treated using a standard conformal technique to a dose of 70 to 74Gy. Patients were classified as low, intermediate or high risk based on PSA, clinical staging and Gleason score. Intermediate risk patients were treated with 0 to 6 months of hormonal therapy (ADT) and high risk patients were offered neoadjuvant and adjuvant ADT. Overall survival (OS) and biochemical relapse-free survival (bNED) were calculated using the Kaplan Meier method. Results The median age of men was 69.6 years with a range from 45 to 87 years. The majority of men had palpable disease (64%) or a Gleason score of 7 (50%). The median PSA (defined as the last PSA prior to radiotherapy or commencement of ADT) was 11.0ng/ml. The majority of patients were either classified as intermediate or high risk (86%). Overall, 61.6% of patients received either neoadjuvant or adjuvant ADT with the higher risk groups more likely to receive hormones. Adjuvant ADT use was more common the higher the risk group. Median follow-up was 92 months. Overall survival (OS) for the entire cohort was 75.7% with a median survival time of 157.1 months. OS for the low, intermediate and high risk groups was 84.5%, 78.4% and 68% respectively. Overall survival was significantly lower in the high risk group compared to the low risk group (p < 0.01). The 8-year biochemical relapse-free survival for the entire cohort was 64.8% with a median time to biochemical failure of 76 months. Biochemical relapse-