Abstract Book

S834

ESTRO 37

EP-1545 Evaluation of a customized workflow to assess rectum and bladder during VMAT prostate cancer RT I. Moschini 1 , E. Donno 1 , A. De Pasquale 1 , A. Terulla 2 , E. Villaggi 2 , D. Piva 1 1 Ospedale Guglielmo Da Saliceto Piacenza, Radioterapia, Piacenza, Italy 2 Ospedale Guglielmo Da Saliceto Piacenza, Fisica Sanitaria, Piacenza, Italy Purpose or Objective Volumetric Modulated Arc Therapy (VMAT) for the treatment of prostate cancer enables a better conformity to the target while sparing the surrounding normal tissues and potentially allows to increase the dose to the target. The scope of this work is to evaluate the feasibility of using a customized workflow in a commercial software to determine volume changes and dose distribution modification to rectum and bladder in every fraction Five patients were selected in this retrospective feasibility study. Patients (median age 73 years) were affected by GS 6 (3+3) low risk prostatic adenocarcinoma and were treated through IGRT (image-guided radiation therapy) using Varian Clinac 2100C/D equipped with kV imaging system with CBCT option. The total prescribed dose for each patient was 70 Gy, in 28 fractions. VMAT treatment plans were created in Eclipse Varian TPS. Daily CBCT (cone-beam CT) were carried out before delivery for on-line match anatomy position verification. After treatment, rectum and bladder volumes were manually delineated on every single CBCT (transferred to MIM 6.6 Software) and then compared with the volume outlined in the planning CT by means of a customized workflow to take into account online image registration and get statistical values of volumes. Furthermore, for each daily CBCT, DVH (Dose-Volume Histogram) for those organs were also evaluated and compared with the planned DVH. Results Total CBCT analyzed were 140. Anatomy changes from planning volumes reach differences of 270 cc for bladder and 123 cc for rectum. Mean variation in the position of center of mass along the 3 directions is up to 1,1 cm for bladder and up to 1,4 cm for rectum. Overall compliance with OAR dose constraints is assessed by frequency values of deviation from those based on 2.5 Gy equivalent QUANTEC: V55Gy, V60Gy for rectum and V60Gy for bladder. Conclusion The impact of interfractional anatomical changes on daily dosimetric OAR constraints can be take into account for replanning strategies by means of MIM software through a customized workflow allow an in-depth quantitative evaluation of daily CBCT. Further investigations are needed to improve statistics and clinical correlations among daily anatomical changes to OAR dose, in order to assess the robustness of the course of RT and get quantitative parameters to guide decision-making replanning evaluation strategies. EP-1546 Outcomes of monotherapeutic permanent brachytherapy for Japanese localized prostate cancer N. Katayama 1 , K. Watanabe 1 , A. Takamoto 2 , Y. Oiwa 2 , H. Okawa 1 , H. Ihara 1 , K. Katsui 1 , M. Takemoto 3 , Y. Nasu 2 , S. Kanazawa 1 1 Okayama University Graduate School of Health Sciences, Department of Radiology, Okayama, Japan 2 Okayama University Graduate School of Health Sciences, radiation treatment. Material and Methods

Department of Urology, Okayama, Japan 3 Himeji Red Cross Hospital, Department of Radiotherapy, Himeji, Japan Purpose or Objective Few reports of outcome following monotherapeutic permanent prostate brachytherapy (PPB) in Japanese patients with localized prostate cancer (PCa) are available. The 13 year experience of PPB at a single center with localized PCa is reported. Material and Methods Between 2004 and 2016, the outcomes of 500 patients with low-risk or Gleason score (GS) 3+4 or less intermediate-risk PCa and with >6 months follow-up were analyzed from a cohort of 595 patients treated with PPB. All patients were treated with iodine-125 seeds. Prescription dose was 144 Gy. No patient received supplemental external beam radiotherapy. The clinical factors including pathological data reviewed by a central pathologist and follow-up data were prospectively collected. Biochemical recurrence was analyzed by the Phoenix (nadir + 2 ng/ml) definition. Urinary and rectal morbidity was evaluated using the National Cancer Institute - Common Terminology Criteria for Adverse Events, version 3.0. The Kaplan-Meier method was used to calculate rates of biochemical freedom from recurrence (BFR), disease specific survival (DSS), overall survival (OS), and morbidity. The factors associated with BFR were identified by the Cox proportional hazard The median age was 66.9 (range, 50-78) years. 41.8% received neoadjuvant hormone therapy (NAHT). Median follow-up period was 5.0 (range, 0.5-12.7) years. The 6- year BFR, DSS, and OS rates were 91.7% (low-risk: 93.6% and GS 3+4 or less intermediate-risk: 89.1%), 100%, and 97.5%, respectively. Grade 2, 3 urinary, and Grade 2 rectal toxicity was observed in 0.6%, 1.4%, and 0.8%, respectively. Multivariate analysis indicated that the dose irradiating 90% of the prostate volume (prostate D90) (p = 0.010), initial prostate-specific antigen (PSA) level (p = 0.027), and GS (p = 0.029) were significantly associated with BFR, while age, prostate volume, and NAHT were insignificant (Table 1). The median prostate doses and the 6-year BFR rates were 101.6 Gy and 86.9% for patients treated in 2004–2005 (n = 134), and 169.0 Gy and 93.8% for those treated in 2006–2016 (n = 366). model. Results