Abstract Book

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ESTRO 37

this analysis (5 out of 170 randomized pts were never treated). Low-, intermediate-, and high-risk presentation was respectively 22%, 63%, and 15% (arm A) and 22%, 64%, and 14% (arm B). Six-month androgen deprivation was used in 44% and 45% of pts in arm A and B, respectively. A toxicity stopping rule was activated during the first 3-months of patients’ follow-up though was never triggered. Grade-2 GU toxicity rates at baseline, 5fx, and W12 were 2%, 17%, and 11% vs. 5%, 19% and 6% for pts in arms A and B, respectively (mainly moderate irritative and voiding symptoms). Only one case of obstructive grade-3 GU toxicity was observed at W12 in arm B (TURP-dependent). Two cases of grade-2 GI toxicity (2.5%) were observed at 5fx in arm A. During months 6 to 18, the incidence of grade-2 GU toxicity was 8% and 4% in arms A and B, respectively. One case of grade-3 GU toxicity (0.4%) was observed in arm A. The incidence of grade-2 GI toxicity was below 2% in both arms. Concerning IPSS-based QoL rates, the rate of pts satisfied at baseline, W12 and 18-months were 80%, 78%, and 89% for arm A and 77%, 80% and 88% for arm B, respectively. No changes in EORTC QLQ-PR25 scores for GU, GI, and sexual domains were observed in both arms between baseline and W12, while an improvement was observed at 18 months for GU domains. Conclusion With a minimum follow-up of 18-months it is worth to underline the good tolerance and toxicity profile of both treatment arms in this study with minimal impact on GU QoL. Nonetheless, the potential influence of OTT and urethra-sparing on outcome and long-term tolerance requires a much longer follow-up to confirm these preliminary good results. OC-0504 5-year efficacy and quality of life outcomes of a multi-institutional HDR-Like prostate SBRT trial D. Fuller 1 , B. Kane 2 , C. Medbery 3 , K. Underhill 4 , J. Gray 5 , A. Peddada 6 , R. Chen 7 1 Genesis Healthcare Partners, Radiation Oncology, San Diego, USA 2 California Cancer Center, Radiation Oncology, Fresno, USA 3 Southwest Radiation Oncology, Radiation Oncology, Oklahoma City, USA 4 Benefis Sletten Cancer Institute, Radiation Oncology, Great Falls, USA 5 Sarah Cannon Research Institute, Radiation Oncology, Nashville, USA 6 Penrose-St. Francis Health Services, Radiation Oncology, Colorado Springs, USA 7 University of North Carolina at Chapel Hill, Radiation Oncology, Chapel Hill, USA Purpose or Objective Stereotactic body radiation therapy (SBRT) is an emerging treatment for prostate cancer with potential advantages compared to standard radiation therapy, though with relatively few large series described with long-term data. We report efficacy and quality of life (QOL) results of a multi-center Phase II trial that used a novel, 4-day SBRT regimen. Material and Methods 259 patients with biopsy-proven prostate adenocarcinoma were enrolled from 18 centers: 112 with low-risk (LR), and 147 with intermediate-risk (IR) disease. Patients were treated with SBRT, delivering a heterogeneous isodose distribution emulating High Dose Rate (HDR) brachytherapy, to 38 Gy in 4 fractions. Toxicities were assessed using CTCAE v3 criteria, biochemical failure defined by the Phoenix definition, and Quality of Life (QOL) assessed using the Expanded Prostate Cancer Index Composite Short Form (EPIC-26) questionnaire capturing urinary, bowel, sexual, and hormonal functions.

Conclusion In this population of localized PC patients treated from 2011-2016, TR following the use of ADT-RT was variable. Using pre-treatment T levels, ADT duration, BMI, age, and race, a predictive nomogram can estimate the likelihood of TR. OC-0503 Weekly vs. every-other-day prostate cancer SBRT: 18-months results from a randomized phase II trial T. Zilli 1 , S. Jorcano 2 , S. Bral 3 , C. Rubio 4 , A. Bruynzeel 5 , A. Oliveira 6 , U. Abacioglu 7 , H. Minn 8 , Z. Symon 9 , R. Miralbell 10 1 Hôpitaux Universitaires de Genève, Radiation Oncology, Geneva, Switzerland 2 Teknon Oncologic Institute- Barcelona- Spain, Radiation oncology, Barcelona, Spain 3 Onze-Lieve-Vrouwziekenhuis- Aalst- Belgium, Radiation oncology, Aalst, Belgium 4 Hospital Universitario Sanchinarro- Madrid- Spain, Radiation Oncology, Madrid, Spain 5 VU University Medical Center- Amsterdam- the Netherlands, Radiation Oncology, Amsterdam, The Netherlands 6 Portuguese Institut of Oncology- Porto- Portugal, Radiation Oncology, Porto, Portugal 7 Neolife Medical Center- Istanbul- Turkey, Radiation Oncology, Istanbul, Turkey 8 University Hospital Turku- Turku- Finland, Radiation Oncology, Turku, Finland 9 Sheba Medical Center- Ramat Gan- Israel, Radiation Oncology, Ramat Gan, Israel 10 Geneva University Hospital- Geneva- Switzerland and Teknon Oncologic Institute- Barcelona- Spain, Radiation Oncology, Geneva and Barcelona, Switzerland Purpose or Objective To present the 18-month toxicity results from a prospective multicenter phase II randomized trial of short vs. protracted urethra-sparing stereotactic body radiotherapy (SBRT) for localized prostate cancer (PCa). Material and Methods From 08/2012 through 12/2015, 170 patients (pts) from nine European institutions with cT1c-3aN0M0 PCa and a low risk of nodal involvement (≤20%, according to Roach et al.) were recruited and randomized according to two different overall treatment time (OTT) schedules: either 9 days (arm A, 84 pts), or 28 days, once-a-week, the same week-day (arm B, 86 pts).The prescribed dose was 36.25 Gy in 5 fractions of 7.25 Gy to the prostate ± seminal vesicles in both arms. The prostatic urethra, with a surrounding margin of 3 mm, received a lesser dose of 5 x 6.5 Gy = 32.5 Gy. All patients were treated either with a VMAT or IMRT technique under stereotactic conditions using Novalis linacs and ExacTrac image-guided technology. Genitourinary (GU) and gastrointestinal (GI) toxicity (CTCAE v4.03 grading scale), IPSS, and QoL scores (EORTC QLQ-PR25) were assessed at baseline, at the 5 th fraction (5fx), 12 th weeks (12W) (acute toxicity) and every 6 months since SBRT. Results 82 (median age 70 years) and 83 (median age 69 years) pts, respectively, from arms A and B, were retained for