ESTRO 2020 Abstract Book

S58 ESTRO 2020

were not assessed because of the low prevalence of toxicity per subdomain. Results Four years following treatment, the cumulative incidence for GI toxicity ≥ grade 2 was 22.4%. The cumulative incidences for acute and late GI toxicity ≥ grade 2 were 13.1% and 11.6%, respectively. A dose-toxicity effect for both D2cc and D50% was observed with un- and adjusted ORs of 1.05 and 1.09 for cumulative GI toxicity, respectively (Table 1), indicating higher odds of GI toxicity ≥ grade 2 per increase in rectal dose with steps of 1Gy. For the subdomains, an association with proctitis and fecal incontinence for D2cc and D50% was found, with the strongest association for the rectal D50%. The effect estimates for the diarrhea and rectal bleeding domains are not presented since the model did not converge because of very low prevalence ≥ grade 2 toxicity at some time points. Table 1. Mixed model for repeated measurements GI toxicity versus DVHs in patients with GI toxicity ≥ grade 2 versus patients with < grade 2 toxicity

The numbers of low-, intermediate-, and high-risk group patients were 49 (15%), 130 (41%), and 142 (44%), respectively. The median follow-up period of the surviving patients was 5.1 years (range, 1.1–8.5 years). The 5-year BRFS rates of the low-, intermediate-, high-risk groups were 95.7%, 92.2%, and 92.6%, respectively. The disease-specific survival of the entire group was 100%. Acute (n=0) and late (n=2; 0.6%) G2 gastrointestinal (GI) toxicities were observed. Acute (n=19; 5.9%) and late (n=4; 1.2%) G2 genitourinary (GU) toxicities occurred, including the acute (n=1; 0.3%) and late (n=1; 0.3%) G2 hematuria. None ≥G3 toxicities were observed. Conclusion The 12-fractionated CIRT at 51.6 Gy (RBE) for localized prostate cancer was effective and showed low toxicity. PH-0116 Stereotactic radiotherapy for prostate cancer: preliminary results of a phase II prospective trial V.P. Nguyen 1 , H. Alzin 2 , L. Celine 1 , L. Harzée 3 , S. Joseph 3 , M. Untereiner 1 , B. Frédérick 1 , S. Biver 1 , Z. Bodgal 1 , S. Philippi 1 , P. Nickers 1 1 Centre François Baclesse, Radiotherapy Department, Esch-sur-Alzette, Luxembourg ; 2 Kirchberg Hospital, Urology, Luxembourg, Luxembourg ; 3 Centre François Baclesse, Physics Department, Esch-sur-Alzette, Luxembourg Purpose or Objective Data from phase III prospective trials comparing more conventional RT and SBRT are awaited while the use of SBRT is increasing by extrapolating the results of HDR Brachytherapy. Toxicity and QOL remain the major factors to determine a treatment modality in prostate cancer especially in older patients since until now overall survival was not improved with moderate or extreme hypofractionnation. Our preliminary results and methodology using the binomial law to monitor the safety during such a trial are presented. Material and Methods 150 patients > 70 years were prospectively and consecutively included in a phase II trial from 4/2014- 7/2018 (NCT03235557). Low (CAPRA 0-2) and Intermediate (CAPRA 3-5) risk patients received 5 fractions of 7.25 Gy (36.25 Gy), and High risk (CAPRA 6-10) 5 fractions of 7.5 Gy (37.5 Gy) prescribed on the 80% isodose over 9 days. RT was delivered with a Cyberknife M6 while the tracking was based on 2 pairs of linked fiducial markers in the prostate. 1.5-T MRI was performed at diagnosis for contouring and at 3-year follow up to confirm the resolution of the initial nodules. Toxicities were scored using the CTCAEv4 and quality of life (QOL) with IPSS and IEFF5 scores. Biochemical control follows the Phoenix definition. The preliminary results of the first 73 patients with a median follow-up of 36 months are presented. According to the binomial law with an assumption of <5% risk of severe toxicity, 73 patients is the minimum number of patients with no severe toxicity required to demonstrate the safety of this technique in a larger amount of patients with a 95% confidence interval. Results No early nor late grade > 3 toxicity was observed. 19.2% of patients complained of late grade 1-2 toxicity (2 grade 2 (2,7%) proctitis, 1 grade 2 (1,4%) dysuria). Mean urinary QOL at baseline and at the end of follow up were 1.23 ± 1.12 and 0.83 ± 0.94 respectively (p>0.05). Mean IPSS at baseline and at the end of follow up were 4.26 ± 4.35 and 3.53 ± 2.72 (p>0.05). 3-year biochemical control were respectively 100%, 92.5% and 54.5% considering low, intermediate and high risk prognosis. 5 patients suffered from clinical recurrence with 2 local, 4 nodal and 2 metastatic recurrences. MRI complete response at 3 years was 96.7% (29/30) for the 30 first patients with a complete 3-year-follow-up. As no severe toxicity was observed at 36 months in this population, according to the binomial law,

Conclusion Rectal dose-volume effects on GI toxicity were observed for D2cc and D50% DVH parameters. The range in rectal dose in the FLAME study was limited due to strict rectal dose constraints that were prioritized over focal boost dose. Nevertheless, even in the small range of dose- variation, a significant dose-toxicity effect between rectal DVH parameters and GI toxicity was observed. Therefore, further increasing the rectal dose is not desirable. PH-0115 Five-year outcomes of 51.6 Gy (RBE) in 12- fractionated carbon-ion RT for localized prostate cancer H. Sato 1 , G. Kasuya 2 , T. Chang 2 , H. Makishima 2 , K. Nemoto 1 , H. Tsuji 2 1 Yamagata University Faculty of Medicine, Radiation Oncology, yamagata, Japan ; 2 QST Hospital- National Institutes for Quantum and Radiological Science and Technology, Radiation Oncology, Chiba, Japan Purpose or Objective Although 51.6 Gy (relative biological effect [RBE]) in carbon-ion radiotherapy (CIRT) at 12 fractions over a 3- wk period has been performed since 2010 and is now regarded as standard CIRT treatment, there is no report of clinical outcomes with long-term follow-up after CIRT using the dose prescription. This retrospective analysis determined the post-CIRT clinical outcomes of patients treated at our institution at the dose prescription with a >5-year median follow-up. Material and Methods A total of 321 patients with localized prostate cancer who received CIRT at 51.6 Gy (RBE) in 12 fractions in one of two protocols (1002 and 9904-4) between July 2010 and February 2014 were analyzed. Biochemical relapse-free survival (BRFS) defined per the Phoenix definition and the survival rates were calculated. The incidence of acute and late adverse events was evaluated based on the Common Terminology Criteria for Adverse Events ver. 4.0. Results