ESTRO 2020 Abstract Book

S624 ESTRO 2020

Gemelli - IRCCS- Università Cattolica del Sacro Cuore, Dipartimento di Scienze Radiologiche- Radioterapiche ed Ematologiche-UOC di Radioterapia Oncologica- Gemelli- ART, Rome, Italy ; 7 Fondazione "Giovanni Paolo II"- Università Cattolica del Sacro Cuore, UO di Fisica Sanitaria, Campobasso, Italy Purpose or Objective Several trials showed a benefit in prostate cancer survival outcomes with dose escalation, with a higher toxicity rate. Aim of this study was to show the results in terms of late toxicity and long term outcomes on a series of prostate cancer patients treated by an integrated boost to the dominant intraprostatic lesion (DIL). Material and Methods Inclusion criteria of the study were: histologically proven adenocarcinoma of the prostate; cT2/3N0M0 stage, based on abdominal and pelvic Magnetic Resonance Imaging and bone scan; Gleason Score < 8; nodal involvement risk less than 20% (calculated by Roach formula); age >18 years; Eastern Cooperative Oncology Group performance status ≤ 2. The trial was approved by the Institutional Ethics Committee. Patients were treated using Intensity Modulated Radiotherapy, with a simultaneous integrated boost to the DIL, defined on the staging MRI. Prostate and seminal vesicles prescribed dose was of 72 Gy/1.8 Gy per fraction; while DIL received 80 Gy / 2 Gy per fraction. Androgen deprivation therapy was administered according to guidelines. The primary endpoint was to evaluate acute toxicity, in order to reduce the rate of acute grade > 2 GI toxicity as already reported in the preliminary analysis. Secondary endpoints were late toxicity and biochemical disease-free survival. Kaplan-Meier product-limit method was used. RTOG scale was used to evaluate toxicity. Results Forty four patients were enrolled, with a median age of 73 (59-81). Median follow up was 66.5 months (25-144 months) . The 34.1% of patients were classified in the intermediate risk group, while the others in the high and very high risk group, according the current guidelines. Actuarial 5-year late GI toxicity free survival was: 76.6% of G1; 100% of G3. Actuarial 5-year late GU toxicity free survival was: 88.8% of G1; 97.6% of G3. Nobody experienced G4 toxicity. Biochemical Disease Free Survival was of 94.9% at 5 years, with all patients experimented local control. Five-year overall survival was of 94.6% and 96.9% the metastasis free survival. Conclusion The reported results, in term of toxicity and survival outcomes are encouraging in our sample. Further studies, even on-going or with the use of more accurate imaging methodologies could demonstrate the utility of a boost to DIL. PO-1186 Impact of a low FODMAP diet on rectal gas and rectal volume during radiotherapy of prostate cancer C. Schaefer 1 , C. Zamboglou 2 , N. Volegova-Neher 2 , C. Martini 2 , N.H. Nicolay 2 , N. Schmidt-Hegemann 1 , P. Rogowski 1 , M. Li 1 , C. Belka 1,3 , A. Grosu 2,4 , T. Brunner 5 1 Ludwig-Maximilians-Universität München- University Hospital, Department of Radiation Oncology, Munich, Germany ; 2 Albert-Ludwigs-Universität Freiburg- University Hospital, Department of Radiation Oncology, Freiburg, Germany ; 3 German Cancer Consortium DKTK, Partner Site Munich, Munich, Germany ; 4 German Cancer Consortium DKTK, Partner Site Freiburg, Freiburg, Germany ; 5 Otto-von-Guericke-Universität Magdeburg- University Hospital, Department of Radiation Oncology, Magdeburg, Germany Purpose or Objective Small inter- and intrafractional prostate motion was shown to be a prerequisite for precise radiotherapy (RT) of

prostate cancer (PCa) to achieve good local control and low rectal toxicity. As rectal gas and rectal volume are known to have a relevant effect on prostate motion, this study aims to reduce these parameters by using a Low FODMAP Diet (LFD) and to show feasibility of this intervention. Material and Methods We compared a prospective intervention group (IG, n = 25) which underwent RT for PCa and whose patients were asked to follow a LFD during RT with a retrospective control group (CG, n = 25) which did not get any dietary advice. In the planning CT scan and all available cone beam CT scans rectal gas was classified based on a semiquantitative score (scale from 1 to 5) and rectal volume was measured. Furthermore, patients’ compliance was evaluated by a self-assessment questionnaire. Results Clinical and treatment characteristics were well balanced between both groups. A total of 266 (CG, 10.6 per patient) and 280 CT scans (IG, 11.2 per patient), respectively, were analysed. The frequency distribution of gas scores differed significantly from each other ( p < .001) with the IG having lower gas scores. Rectal volume was smaller in the IG (64.28 cm 3 , 95% CI 60.92 – 67.65 cm 3 , SD 28.64 cm 3 ) than in the CG (71.40 cm 3 , 95% CI 66.47 – 76.32 cm 3 , SD 40.80 cm 3 ) ( p = .02). Mean intrapatient standard deviation as a measure for the variability of rectal volume was 22 cm 3 in the IG and 23 cm 3 in the CG ( p = .81). Patients’ compliance and contentment were satisfying. Conclusion The use of a LFD significantly decreased rectal gas and rectal volume. LFD was feasible with an excellent patients’ compliance. However, prospective trials with a larger number of patients and a standardized evaluation of gastrointestinal toxicity and quality of life are reasonable. PO-1187 A gene signature-based model to predict BCR- free survival after radical prostatectomy M. Li 1 , R. SHI 1 , B. Claus 1 1 University Hospital- LMU Munich, Department of Radiation Oncology, Munich, Germany Purpose or Objective More precise methods to identify high-risk prostate cancer (PCa) patients who may suffer biochemical recurrence (BCR) after radical prostatectomy is a critical issue. We sought to construct an integrated model based on a molecular signature and clinicopathological features to optimize the risk stratification for BCR and improve biochemical recurrence-free survival (BCRFS) prediction in PCa patients after radical prostatectomy. Material and Methods Using high-throughput screening and least absolute shrinkage and selection operator (LASSO) in the training set, a gene signature for BCRFS was established and its prognostic value was validated in other five independent datasets. Multivariate Cox regression analysis was performed to evaluate the importance of risk for BCR. Time-dependent receiver operating characteristic (tROC) was used to evaluate the predictive power. Combined with traditional clinicopathological variables (Gleason score, pathological stage and surgical margin status), a decision tree was built to improve the risk stratification. Bioinformatic analyses were performed to explore potential biological processes underlying the gene signature. Results The gene signature exhibited powerful capacity in discriminating high-risk BCR patients, and multivariate Cox regression analysis demonstrated that the gene signature consistently acted as a risk factor for BCR in all six cohorts. The decision tree was able to identify high-risk subgroup powerfully. Bioinformatic analyses suggested that the gene signature was related with cell cycle process in PCa.