ESTRO 2020 Abstract book

S270 ESTRO 2020

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 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 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