ESTRO 2020 Abstract book

S718 ESTRO 2020

Data regarding the possible reduction of the immune response in elderly patients and its negative effect on the anti-tumour response, purportedly leading to a decreased efficacy to immune checkpoint inhibitor (ICI) therapy, is still lacking. The aim of this study was to assess the role of the combination of ICI and stereotactic ablative radiotherapy (SABR) in elderly metastatic cancer patients We conducted a prospective study including metastatic patients over 75 years old (lung, melanoma and bladder carcinoma) who had experienced disease progression while on ICI (anti-PD1/L1) treatment. SABR was performed by volumetric-modulated arc therapy and each fraction was delivered in a separate interval of 48 hours. Objective overall response (OR) including complete response (CR), partial response (PR) and stable disease (S), acute toxicity (CTCAE v.4.3), and abscopal response (AR) were measured. One to three metastases were selected on each patient for SABR treatment. All patients had received at least 2 cycles of ICI prior to SABR. In order to evaluate the abscopal effect, 1-2 non-irradiated lesions were selected. AR was defined as 25% reduction in any non- radiated predefined measurable lesions. These lesions were assessed according to RECIST (v1.1) by CT, MRI or PET at 8-week intervals. Results From July 2017 to December 2018, 12 patients who had received anti-PD-1/L-1 immunotherapy [nivolumab (n=2), pembrolizumab (n=9) or atezolizumab (n=2)] were included. All lesions received SABR doses > 6 Gy/fraction, with a median dose of 35 Gy/5 fractions (BED 10 = 59.5 Gy). Eleven patients received doses > 50 Gy (BED 10 ). After a 12- month median follow-up (6-19 months), the acute ICI toxicity profile was similar before and after SABR. Median overall survival (OS) was 12,8 months (SD 0.5, IC95% 9,2- 17). Local response was reported in 9 patients (75%). AR was observed in 5 patients (42%), 2 of whom had CR, 1 PR. Median time from SABR to AR was 2 months. Four patients with AR are alive to date. Overall, 4 patients (33%) presented OR and 2 patients (17%) achieved a sustained systemic CR. 3 patients (25%) have required a new systemic treatment. After SABR, median OS was 12,8 months (SD 0.8, IC95% 1.1- 14.6). From diagnosis, median OS 26,5 months (SD 1.8, IC95% 22.8-30.1) with 50% of patients alive at 1 year. No radiotherapy-related toxicity grade 3-4 was reported. Conclusion Our results show that in elderly metastatic patients in progression to ICI, I-SABR could rechallenge the immune system resulting in high local and abscopal effect improving survival with maintenance ICI treatment. in progression to ICI. Material and Methods PO-1273 Infrastructure and staffing in the EORTC Radiation Oncology Group’s international network J. Willmann 1 , A.F. Monti 2 , P. Poortmans 3 , W. Grant 4 , E. Clementel 5 , C. Corning 5 , N. Reynaert 6 , C.W. Hurkmans 7 , N. Andratschke 8 1 EORTC Headquarters, Medical Department, Brussels, Belgium ; 2 Ospedale Niguarda Ca Granda, Department of Medical Physics, Milan, Italy ; 3 Institut Curie, Department of Radiation Therapy, Paris, France ; 4 Gloucestershire Hospital NHS Foundation Trust - Cheltenham General Hospital, Oncology Department, Cheltenham, United Kingdom ; 5 EORTC Headquarters, Data Management, Brussels, Belgium ; 6 Institut Jules Bordet, Medical Physics Department, Brussels, Belgium ; 7 Catharina Ziekenhuis, Department of Radiotherapy, Eindhoven, The Netherlands ; 8 UniversitätsSpital Zürich, Department of Radiation Oncology, Zurich, Switzerland Poster: Clinical track: Health services research / health economics

Purpose or Objective The EORTC Radiation Oncology Group (ROG) collects characteristics of its member radiation oncology (RO) departments using a dedicated Facility Questionnaire (FQ). We aimed to report the current departmental characteristics and describe developments over time. Material and Methods On 27/08/2019, the FQ database was exported. Since the FQ is valid for 2 years, only institutions that created or updated it between August 2017 and August 2019 were included in this report. Parameters on institutional status, staffing and infrastructure were extracted and compared to previously published results [1]–[3]. Results Institutional Data 161 member institutions from 25 countries were included: 21 in Europe, 2 in North America (Canada, USA), 1 in Africa (Egypt) and 1 in Australia (Australia). The country with most member institutions is Germany (n=25), followed by France (n=21), Canada, Italy and Spain (n=17 each). 116 (72%) members are public centers, 98 (61%) are university- affiliated. 151 (94%) institutions reported entering patients in clinical trials, including but not limited to EORTC trials. Staffing & Workload The average number of patients treated per department increased to 2565 per year (2013: 2381) (Tab. 1). Still, there was a decline in the number of patients treated per year per physicists to 331 (2013: 354) and to 228 per radiation oncologists (2013: 242) (Fig. 1a). For RTTs, the number of patients treated per year increased to 107 (2013: 86). Infrastructure On average, there are 5.2 MV treatment units per department (median 4, range: 1-20) and 1.5 simulators (median 1, range 1-4).There are 844 MV units in total. Of these, 741 are Linacs (mean 4.6 per department, range: 1- 17), not including TomoTherapy and CyberKnife, which are owned by 32 (20%) and 18 (11%) departments, respectively. GammaKnife is used in 17 centers (11%) and 2 report still having Co-60 units installed. MRI Linacs are used by 2 institutions (1 Elekta Unity and 1 ViewRay MRIdian). IMRT is widely available in 95% of the departments (2013: 94%), 81% are capable of delivering VMAT (Fig. 1b). An increasing number of institutions delivers complex techniques such as extracranial SBRT (2013: 65% vs 2019: 86%). Intracranial SRS and fractionated SRT are delivered in 41% and 75% of the departments, respectively.The rate of institutions that own a dedicated MRI scanner stayed at 15%, while the number of institutions that own a PET/CT scanner increased from 4% to 9%.