ESTRO 2021 Abstract Book

S1128

ESTRO 2021

Purpose or Objective Proton therapy (PT) for localized prostate cancer using the wobbler method (passive scattering) has been reported to have favorable biochemical control and late toxicities rates. In recent years, PT has been gradually shifting to scanning methods from wobbler methods. We performed a planning study to compare the dose distribution of the scanning method with that of the wobbler and the volumetric modulated arc therapy (VMAT) for patients with localized prostate cancer. Materials and Methods Thirty prostate cancer patients treated in 2016-2018 were randomly selected. Three radiotherapy plans were created for each patient with the same prescribed dose (76.0 Gy or Gy [RBE] in 38 fractions) and compared using dose-volume histograms. Dose constraints were clinical target volume (CTV) D98 ≥ 73.0 Gy (RBE), rectal wall V65 < 17%, V40 < 35%, and bladder wall V65 < 25% and V40 < 50%, respectively. CTV doses, bladder and rectum wall dose volumes (V10 - V75), Dmean, and Dmax were calculated and tested by Wilcoxon's rank-sum test. P < 0.05 was determined to be statistically significant. Results The dose coverage of CTV was favorable with the scanning and the wobbler than with the VMAT. Wide ranges of the rectal and bladder wall volumes of V10 - V70 were significantly lower with the scanning method compared with the wobbler method and the VMAT (P < 0.05). The wobbler method yielded better dose distribution of the rectum and bladder wall in the low dose range (V10-20) and near the maximum dose compared with the VMAT. Conclusion Compared with the wobbler method and the VMAT, the scanning method enables further reduction of the rectal and bladder doses while maintaining the CTV dose. PO-1378 Metastasis-directed therapy for oligorecurrent prostate cancer: a pooled analysis P. Ost 1 , A. Berlin 2 , S. Siva 3 , D. Reynders 4 , R. Phillips 5 , R. Glicksman 6 , F. Faroudi 7 , V. Fonteyne 8 , M. Deek 9 , P. Chung 6 , D. Murphy 10 , P. Tran 11 1 Ghent University, Structure and Repair, Ghent, Belgium; 2 University of Toronto; Radiation Medicine Program, Princess Margaret Cancer Centre, Department of Radiation Oncology, Toronto, Canada; 3 Peter MacCallum Cancer Center, Radiation Oncology, Melbourne, Australia; 4 Ghent University, Department of Applied Mathematics, Computer Science and Statistics, Ghent, Belgium; 5 Mayo Clinic, Radiation Oncology, Rochester, USA; 6 University of Toronto; Radiation Medicine Program, Princess Margaret Cancer Centre, Radiation Oncology, Toronto, Canada; 7 Peter MacCallum Cancer Center, Radiation Oncology, Melbourne, Belgium; 8 Ghent University Hospital, Radiation Oncology, Ghent, Belgium; 9 John Hopkins, Radiation Oncology, Baltimore, USA; 10 Peter MacCallum Cancer Center, Urology, Melbourne, Australia; 11 John Hopkins, Radiation Oncology, Ghent, USA Purpose or Objective Prospective data for metastasis-directed therapy for oligorecurrent prostate cancer (PCa) have been limited to single arm or small phase 2 randomized studies. We conducted an individual patient data meta-analysis to characterize the safety and clinical benefit of metastasis-directed therapy (MDT) in oligorecurrent PCa. Materials and Methods We searched for prospective trials investigating the safety and clinical benefit of MDT in oligorecurrent PCa in trial registries and conference proceedings until January 2020. Inclusion criteria were single- or multi-arm prospective trials including only patients with recurrent prostate cancer and a limited number of recurrences (ie, ≤5 sites of extracranial disease) undergoing MDT (surgery or radiotherapy). ADT-free survival was analyzed as the primary outcome, and biochemical relapse free survival as secondary outcome. If HR were not constant across the different trials, we calculated standardized survival curves, analyzing the trials separately and pooling the adjusted log HR, weighted by sample size. The following covariates were examined with the interaction test: PSA doubling time and localization of disease (nodal vs extra-nodal). Results We identified 4 trials with published results: 2 single arm and 2 randomized trials, representing in total 174 patients (MDT: 72%, active surveillance, AS: 28%). Patient characteristics differed with respect to imaging at inclusion (different PET-tracers), PSA doubling time and localization of disease (nodal vs extra-nodal). For ADT-free survival, non-proportional hazards were detected, but not for biochemical relapse-free survival. ADT-free survival is improved with MDT over AS (HR: 0.56, 95%CI 0.34 – 0.94, p=0.03) across all covariates, as well as biochemical-free survival (HR: 0.44, 95%CI 0.29 – 0.67, p<0.01). Grade 2 and 3 toxicity were observed in 3% and 2%, respectively, of cases treated with MDT. Conclusion MDT improves both biochemical-free and ADT-free survival as compared to active surveillance with low rates of grade 3 or higher toxicity. PO-1379 Patient- vs. physician reported morbidity following radiotherapy of high-risk prostate cancer S.E. Petersen 1 , S. Hansen 2 , P.M. Petersen 3 , H. Lindberg 4 , M. Moe 5 , J.B. Petersen 6 , L.P. Muren 7 , M. Høyer 1 , L. Bentzen 8 1 Aarhus University Hospital, Danish Center for Particle Therapy, Aarhus, Denmark; 2 Odense University Hospital, Department of Oncology, Odense, Denmark; 3 Rigshospitalet, Department of Oncology, Copenhagen, Denmark; 4 Herlev University Hospital, Department of Oncology, Herlev, Denmark; 5 Aalborg University Hospital, Department of Oncology, Aalborg, Denmark; 6 Aarhus University Hospital, Department of Medical Physics, Aarhus, Denmark; 7 Aarhus University Hospital, Danish Center for Particle Therapy, Aarhus , Denmark; 8 Aarhus University Hospital, Department of Oncology, Aarhus, Denmark

Purpose or Objective Whole pelvic irradiation is considered a standard treatment option for high-risk prostate cancer (PC) patients.