ESTRO 2025 - Abstract Book

S1378

Clinical - Lung

ESTRO 2025

We report the treatments of the first five patients. The SBRT schedules ranges from 5 to 8 fractions with a total dose from 42 to 60 Gy. We analyzed patients and treatment characteristics, beam-on time, beam-hold (time of beam interruption due to gating), duty cycle (% of the total beam-on time of the entire delivery phase), positioning shifts. Results: Between November 2023 and May 2024, 5 patients were submitted to lung SBRT on MR-Linac. ATS workflow was applied for 8 fractions and ATP for the remaining 24. The treatment was delivered in free-breathing with intrafraction tracking and gating by means CMM. The PTV margin was 5 mm. All patients completed the treatment. The mean duty cycle was 95.63% (95%CI 93.41-97.85). The mean beam-on time was 608.9 seconds (95%CI 552.4 665.4 seconds). Beam-hold occurred in all treatment fractions for a mean beam-hold count of 41.3 instances (95%CI 37.3-56.9). The mean beam-hold time of those treatment fractions was 201 seconds (95%CI 132-291). No baseline shift plan was performed due to persistent target drifts. Acute toxicity (acc. CTCAE v5.0) was very low: only 1 case of grade 1 cough. No grade >=2 toxicity occurred. Conclusion: This is our first experience on clinical application of CMM for lung SBRT on 1.5T MR-linac. The implementation of CMM can guarantee high treatment precision without significant beam-on time increase. The procedure was well tolerated by patients and the acute toxicity rates reported were very low. Digital Poster Lessons from the Pandemic: Impact of COVID-19 on Lung Cancer Care Manuel Luis Blanco-Villar 1 , José Expósito-Hernández 1,2 , Eulalia Navarro-Moreno 3,4 , Adrián Aparicio Mota 5 , José María López Martín 5 1 Radiation Oncology, University Hospital Virgen de las Nieves, Granada, Spain. 2 Instituto de Investigación Biosanitaria, ibs, Granada, Spain. 3 Tumor Registry of Torrecárdenas University Hospital, University Hospital Torrecárdenas, Almería, Spain. 4 Department of Preventive Medicine and Public Health, University Hospital Torrecárdenas, Almería, Spain. 5 Andalusian Public Foundation for Biomedical Research in Eastern Andalusia (FIBAO), University Hospital Torrecárdenas, Almería, Spain Purpose/Objective: This study assesses the impact of the COVID-19 pandemic on lung cancer diagnostic and treatment pathways in a tertiary care center. The analysis focuses on adherence to diagnostic and treatment timeframes, identifies predictors of delays, and examines survival outcomes across three cohorts: pre-pandemic (2019), first pandemic year (2020), and second pandemic year (2021). Material/Methods: This retrospective cohort study evaluated 530 patients diagnosed with lung cancer (NSCLC and SCLC) between 2019 and 2021. Patients were categorized into three cohorts: pre-pandemic (2019), first pandemic year (2020), and second pandemic year (2021). Key intervals analyzed included referral-to-diagnosis, diagnosis-to-first definitive treatment (FDT), and overall survival. Multivariate Cox regression and Kaplan-Meier methods assessed survival and hazard ratios (HRs). The patient flow and cohort inclusion are illustrated in Figure 1 , while overall survival trends are presented in Figure 2. Results: The study included 530 patients: 179 in 2019, 145 in 2020, and 206 in 2021, with 64 patients excluded ( Figure 1 ). Patient characteristics revealed a significant increase in median age (from 65 in 2019 to 67 in 2021, p = 0.0368) and Keywords: MR-Linac, adaptive, gating 2961