ESTRO 2020 Abstract book

S424 ESTRO 2020

were also included in the arm without concurrent cisplatin. Predefined olaparib dose levels were 25mg once daily and 25mg to 300mg bi-daily. Dose escalation was performed using a Time-To-Event Continual Reassessment Method (TITE-CRM) design with a dose limiting toxicity (DLT) observation period of one year. The MTD was defined as the highest dose level below the target DLT probability of 15%. Secondary endpoints included toxicity according to the CTCAE and locoregional control. After observing severe late onset pulmonary toxicity, all patients were re- evaluated for late pulmonary toxicity until death. Results 28 patients were treated. Table 1 describes treatment details and DLT. The MTD of olaparib in combination with radiotherapy only was 25mg once daily with a DLT probability of 14.6%. The triple combination of olaparib, radiotherapy and cisplatin was not tolerable (DLT probability 31% at lowest dose level) due to hematological and esophageal toxicity. At a latency of 1-2.8 years, severe grade ≥ 4 pulmonary toxicity (bronchial strictures, pulmonary fibrosis and fatal hemorrhage) was observed in five patients treated at all olaparib doses, with and without concurrent cisplatin. This was mostly seen in patients in whom at least 30% of the lung volume received 20Gy or more (4 out of 7 patients with lung V20 ≥ 30%, 1 out of 14 patients with lung V20 < 30%, all with a minimal follow-up of one year). The two-year locoregional control was 84%. There were no isolated infield recurrences. Conclusion The identified maximum tolerated dose of the PARP inhibitor olaparib in combination with high dose radiotherapy is 25mg once daily without concurrent cisplatin. Given the observed late onset pulmonary toxicity, it is highly recommended to limit the lung V20 < 30%. This allows for a strategy to improve outcome for LA- NSCLC patients by replacing cisplatin with the radiosensitizer olaparib. Our study stresses the importance of late onset toxicity monitoring in the clinical development of radiosensitizers. OC-0693 Involved-Field Irradiation in Definitive Chemoradiotherapy for Loco-Regional Esophageal Cancer K. Zhao 1 , H. Zhu 1 , E. Rivin Del Campo 2 , C. Yun 1 , J. Ye 3 , Z. Zhu 1 , W. Zhao 1 , J. Zhou 4 , C. Wu 4 , H. Tang 5 , F. Min 1 , L. Li 1 , Q. Lin 6 , Y. Xia 7 , J. Li 8 1 fudan University Shanghai Cancer Center, Thoracic Radiation Oncology, Shanghai, China ; 2 tenon University Hospital- Hôpitaux Universitaires Est Parisien- Sorbonne University, Radiation Oncology, Paris, France ; 3 jiangsu Cancer Hospital-The Affiliated Cancer Hospital Of Nanjing Medical University, Radiation Oncology, Nanjing, China ; 4 affiliated Hospital Of Jiangnan University, Radiation Oncology, Wuxi, China ; 5 zhenjiang First People’s Hospital Affiliated To Jiangsu University, Radiation Oncology, Zhenjiang, China ; 6 the First Affiliated Hospital Of Xiamen University, Radiation

Oncology, Xiamen, China ; 7 fudan University Shanghai Cancer Center Minhang Branch Hospital, Radiation Oncology, Shanghai, China ; 8 fujian Cancer Hospital- Fujian Medical University Cancer Hospital, Radiation Oncology, Fuzhou, China Purpose or Objective To evaluate the feasibility and efficacy of involved-field irradiation in definitive chemoradiotherapy for loco- regional esophageal squamous cell carcinoma. Material and Methods Recurrence pattern and elective nodal failure was analyzed in patients from the previously published ESO- Shanghai 1 trial, who received definitive chemoradiotherapy with involved-field irradiation to 61.2Gy/34Fx using intensity-modulated radiation therapy planning. Nodal regions were delineated with 6 th AJCC map. Elective nodal failure was defined as recurrence in the regional nodal area outside the planning target volume. Incidental irradiation dose of each node and each region was evaluated. Results With a median follow-up of 48.7 months in survivors, the 3-year actuarial rate of overall survival was 53.6%, the median overall survival was 44.8 (95% CI: 34.6-55.0) months. Of the 436 patients included in this study, 258 patients (59.2%) experienced treatment failure. Thirty- seven patients (8.5%) were identified as elective nodal failure, among which 7 patients (1.6%) were elective nodal failure only. The 3-year actuarial rates of elective nodal failure and elective nodal failure only were 89.7% and 97.9%. The median incidental dose of these nodes was 33.2 Gy [Interquartile range (IQR): 1.3-50.7 Gy)]. The median distance of each node to planning target volume was 1.4 cm (IQR: 0.6-4.9 cm). More than a third (38.7%) of these lymph nodes received incidental irradiation dose of more than 40Gy and 41.9% received less than 10 Gy. Conclusion Involved-field irradiation provided a low isolated nodal failure rate and a satisfactory survival outcome. Elective nodal irradiation may be unnecessary in definitive chemoradiotherapy for loco-regional esophageal squamous cell carcinoma. OC-0694 An ESTRO-ACROP Delphi consensus on salvage SBRT for intraprostatic relapse after PCa radiotherapy B.A. Jereczek-Fossa 1 , G. Marvaso 2 , M. Pepa 2 , S.G. Gugliandolo 2 , D. Zerini 2 , S. Gandini 3 , A. Vavassori 2 , B. De Bari 4 , F. Alongi 5 , V. Fonteyne 6 , B. Pieters 7 , P. Hoskin 8 , A. Tree 9 , A. Bossi 10 , P. Cornford 11 , A. Toledano 12 , J. Hannoun-Levi 13 , R. Miralbell 14 , D. Fuller 15 , M. Scorsetti 16 , S. Arcangeli 17 , L. Livi 18 , G. Janoray 19 , D. Pasquier 20 , P. Ost 6 1 università Degli Studi Di Milano - European Institute Of Oncology, Oncology&Hemato-Oncology Dept/Radiotherapy Dept. Of European Institute Of Oncology, Milan, Italy ; 2 ieo European Institute Of Oncology Irccs, Division Of Radiotherapy, Milan, Italy ; 3 ieo European Institute Of Oncology Irccs, Molecular And Pharmaco-Epidemiology Unit- Department Of Experimental Oncology, Milan, Italy ; 4 réseau Hospitalier Neuchâtelois / University Of Lausanne Unil, Radiation Oncology, La Chaux-De-Fonds / Lausanne, Switzerland ; 5 irccs Sacro Cuore-Don Calabria Hospital / University Of Brescia, Advanced Radiation Oncology, Verona, Italy ; 6 ghent University Hospital, Department Of Radiotherapy, Ghent, Belgium ; 7 amsterdam University Medical Centers / University Of Amsterdam, Department Of Radiation Oncology, Amsterdam, The Netherlands ; 8 mount Vernon