ESTRO 2020 Abstract Book

S251 ESTRO 2020

efficacy and safety of SRT combined with TKIs in stage IV metastatic cancer patients. Material and Methods The retrospective international multicenter register study (TOaSTT) collected data on metastatic patients receiving SRT concurrent (≤30d) to TKI. Overall survival (OS) progression free survival (PFS), local control (LC), time to switch of systemic therapy after SRT was analyzed using Kaplan-Meier survival curves and log rank testing. Toxicity was defined by the CTCAE v4.03 criteria. Results Data of 454 SRTs in 158 patients were included. Median FU was 19.9mo (range 1-102mo). The histology was melanoma (29%), NSCLC (44%), RCC (23%) or colorectal cancer (4%). ECOG-PS was 0-1 in 98%. The total GTV volume was median 1cc (range 0.03-23.9) for brain metastases (BM) and median 7.5cc (range 0.54-154-5) for extracranial lesions. The prescribed dose (BED 10 ) was 63 Gy (range 44-114) for brain metastases (BM) and 93Gy (range 53-180) for extracranial lesions. 1y OS, PFS and LC was 59%, 24% and 84%, respectively. TKIs were started before SRT in 77%, with a median of 7mo (range 0-49), 23% started during/after SRT. TKIs were paused or started after SRT in 44%, with a median of 7 (range 1-42) days. There was no significant difference in OS or PFS whether or not TKIs were temporarily paused for SRT. Any grade acute and late SRT-related toxicity occurred in 63 (40%) and 52 (33%) patients, respectively. This was observed mainly in combination with EGFRi or BRAF±MEKi, and was significantly increased when EGFRi (p=0.016) or BRAF±MEKi (p=0.009) were continued during SRT. Severe (≥ grade 3) acute and late SRT-related toxicity occurred in 5 (3%) and 7 (4%) patients, respectively, also mainly in combination with EGFRi or BRAF±MEKi. Although in all but one of these patients, the TKI was not paused during SRT, there was no significant difference in severe toxicity when pausing TKIs or not. The majority (83%) of severe toxicity was observed after SRT of BM. Conclusion Results of this study suggest that SRT concurrent to TKI treatment in metastatic patients achieves good local metastasis control. There was no difference in OS or PFS whether TKIs were paused during SRT or not. Overall, severe toxicity of combined treatment was rare; however, SRT-induced toxicity was mainly observed when SRT was performed concurrently to EGFR inhibitors or BRAF(±MEK) inhibitors. OC-0454 Current radiotherapy practice for children with metastases from solid tumors: SIOPE survey analysis S. Huijskens 1 , P. Kroon 1 , C. Demiroz Abakay 2 , B. Timmermann 3 , J. Giralt 4 , M. Gaze 5 , S. Harrabi 6 , G. Scarzello 7 , A. Alexopoulou 8 , L. Padovani 9 , A. Escande 10 , L. Gandola 11 , S. Supiot 12 , M. Chojnacka 13 , J. Bokun 14 , A. Napieralska 15 , B. Rombi 16 , J.H. Maduro 17,18 , S. Bolle 19 , A. Mussano 20 , H. Mandeville 21 , L. Claude 22 , E. Seravalli 1 , G.O. Janssens 1,18 1 University Medical Center Utrecht, Radiation Oncology, Utrecht, The Netherlands ; 2 Uludag University, Radiation Oncology, Bursa, Turkey ; 3 University Hospital Essen, Department of Particle Therapy, Essen, Germany ; 4 Vall d’Hebron University Hospital, Radiation Oncology, Barcelona, Spain ; 5 University College London Hospitals NHS Foundation Trust, Radiation Oncology, London, United Kingdom ; 6 Heidelberg University Hospital, Radiation Oncology, Heidelberg, Germany ; 7 Veneto Institute of Oncology, Radiation Oncology, Padua, Italy ; 8 Athens General Children's Hospital, Radiation Oncology,

Conclusion This phase I trial confirms that SBRT to all oligometastatic lesions, combined with SOC systemic treatment when available, is extremely safe and leads to excellent local control as well as promising long-term PFS. Since no significant differences in toxicity, local control nor clinically relevant differences in target coverage were observed between the 3 schedules, single-fraction SBRT should probably be preferred, considering both resource- efficiency and patient comfort. OC-0453 Efficacy and safety of stereotactic radiotherapy combined with TKIs for metastatic lesions. S. Kroeze 1 , C. Fritz 1 , O. Blanck 2 , K.H. Kahl 3 , D. Kaul 4 , S. Siva 5 , S. Gerum 6 , A. Claes 7 , N. Sundahl 8 , S. Adebahr 9 , A. Nateghian 10 , M.M. Schymalla 11 , A. Wittig 12 , D. Buergy 13 , M. Geier 14 , M. Szuecs 15 , F. Lohaus 16 , G. Henke 17 , S.E. Combs 18 , M. Guckenberger 1 1 University Hospital Zürich, Radiation Oncology, Zurich, Switzerland ; 2 University Medical Center Schleswig- Holstein, Radiation Oncology, Kiel, Germany ; 3 University Hospital Augsburg, Radiation Oncology, Augsburg, Germany ; 4 Charité-University Hospital Berlin, Radiation Oncology, Berlin, Germany ; 5 Peter MacCallum Cancer Centre, Radiation Oncology, Melbourne, Australia ; 6 University Hospital Munich, Radiation Oncology, Munich, Germany ; 7 University Medical Center Utrecht, Radiation Oncology, Utrecht, The Netherlands ; 8 University Hospital Ghent, Radiation Oncology, Ghent, Belgium ; 9 University Medical Center Freiburg, Radiation Oncology, Freiburg, Germany ; 10 University Hospital Frankfurt, Radiation Oncology, Frankfurt, Germany ; 11 Philipps- University Marburg, Radiation Oncology, Marburg, Germany ; 12 University Hospital Jena, Radiation Oncology, Jena, Germany ; 13 Univerity Hospital Mannheim, Radiation Oncology, Mannheim, Germany ; 14 Ordensklinikum Linz, Radiation Oncology, Linz, Austria ; 15 University Hospital Rostock, Radiation Oncology, Rostock, Germany ; 16 University Hospital Tübingen, Radiation Oncology, Tübingen, Germany ; 17 Kantonsspital St. Gallen, Radiation Oncology, St. Gallen, Switzerland ; 18 Technical University Munich, Radiation Oncology, Munich, Germany Purpose or Objective The increased use of tyrosine kinase inhibitors (TKIs) has resulted in prolonged tumor control and survival in stage IV metastatic cancer. With our expanding knowledge on the diversity of metastatic states, stereotactic irradiation (SRT) is increasingly performed in patients receiving TKI to obtain a durable local control and possibly further extend the time to disease progression. However, currently there is lack of knowledge on the safety and efficacy of this approach. The aim of this study was to examine the