ESTRO 2025 - Abstract Book

S1546

Clinical – Mixed sites & palliation

ESTRO 2025

Material/Methods: Patients treated with SRT for intracranial or extracranial metastases, concurrently (≤30d) with BCT were enrolled in an international multicenter registry study (TOaSTT), which consisted of a retrospective and prospective cohort with identical databases. SRT-related severe acute (<3 months) and late (>3 months, follow-up 24 months) toxicity (CTCAE v4.03) were the primary endpoints, with SRT-related toxicity defined as toxicity in organ systems exposed to radiotherapy. Results: The prospective registry collected data from 514 SRTs in 433 patients from 27 centers between 07/2017 and 08/2019. Retrospectively, data on 570 SRTs in 441 patients were collected between 12/2016 and 07/2018. Concurrent treatment with ICIs was the most common combination in both cohorts (Tables 1-2). Overall rates of severe acute and late toxicity were low: prospectively 5,3% and 6,3%, retrospectively 2,5% and 2,8%. Severe toxicity occurred most frequently after SRT for cranial metastases (prospectively n=18, 6,8%(acute) and n=19, 8,2%(late), retrospectively n=4, 2,6% and n=6, 4,0%). In the prospective cohort, EGFRi/aEGFR treatment was associated with increased severe late toxicity (p<0.01), although absolute toxicity rates in this limited patient population remained small (n=8/44; 18,2%). In the retrospective cohort, only two severe late toxicity events were observed in patients receiving EGFRi/aEGFR (n=2/67, 3,0%). The continuation of BCT during SRT was not associated with increased rates of severe acute or late toxicity: prospectively severe acute toxicity was 5.8% vs 4.5% (OR 1.29, 95%CI 0.54-3.12) and severe late toxicity 7,7% vs 3,5% (OR 2.32, 95%CI 0.87-6.22). In the retrospective cohort this was 4,0% (n=7/177) vs 0,6% (n=1/177) for severe acute toxicity and 3,4% (n=6/177) vs 1,7% (n=3/177) for severe late toxicity. Multivariate analyses will be presented at the ESTRO conference.