S476
Clinical - Gynaecological
ESTRO 2026
particularly in Arm 1, often due to dissatisfaction with not receiving SABR after randomization. Some patients withdrew after disease progression to enroll in competing therapeutic clinical trials. In Arm 2, 16 serious adverse events (SAEs) were reported. Five Grade ≥ 3 SAEs were considered SABR- related, with bowel toxicity being the most frequent. Following DSMB recommendations, investigators reinforced pre-randomization counseling to patients, strengthened site- specific dropout monitoring, and enhanced SABR safety education to clinicians. From the pattern-of-care survey involving 80 gynecologic oncologists (GOs) and 36 radiation oncologists (ROs), 68.8% of GOs and 91.7% of ROs considered radiotherapy effective. Local control was the most prioritized goal in both groups. Among GOs, 68% had partial knowledge of SABR, citing low side effects (65%) as an advantage and limited indications (81%) as a disadvantage. SABR planning practices were consistent for lung and liver lesions but highly variable for abdominal lesions across ROs (p = 0.029). Conclusion: The SABR-ROC trial is nearing full accrual and is anticipated to meet the enrollment target by end of 2025. Like other randomized phase III radiotherapy trials, challenges related to premature discontinuation have emerged. Future analyses should address these biases, and continued efforts should focus on improving education regarding the clinical utility of SABR, particularly among GOs, to support its adoption and consistent implementation. Clinical Trial number: NCT05444270. Keywords: Ovarian cancer, Stereotactic ablative radiotherapy
Digital Poster 3868
Impact of treatment interruptions on tumor regression in cervical cancer patients treated with MR-guided radiotherapy on the 1.5T Unity MR-Linac Perla Zidane 1 , Thomas Berger 1 , Angela Boros 1 , Ionela Caraivan 1 , Mazen Moussallem 2,3 , Corina Udrescu 1 , Olivier Chapet 1 1 radiation oncology department, CHU Lyon Sud, Lyon, France. 2 Medical imaging department, Holy family university, Batroun, Lebanon. 3 Research and development department, Healthy innovations, Rachiine, Zgharta, Lebanon Purpose/Objective: Treatment interruptions during radiotherapy can be frequent, yet their impact on treatment response in cervical cancer remains poorly understood. This study evaluated the impact of treatment interruptions on tumor volume kinetics and treatment response in women treated with the Unity® 1.5T MR-Linac. Material/Methods: Patients with cervical cancer treated between July 2021 and July 2025 were analyzed retrospectively.IMRT was used to deliver 45Gy in 25 fractions, with an integrated boost to 55 Gy in case of pelvic nodal involvement. Daily T2-weighted MR images were used to delineate tumor volumes, which were validated by two expert radiation oncologists. To analyze regression dynamics, treatment was divided into three phases: early (fractions 1–8), middle (fractions 9–17), and late (fractions 18–25). Inter-fraction intervals were classified as consecutive (1-day interval) or interrupted (>1-day interval, e.g. weekends/holidays). For each patient, cumulative volume regression curves were generated separately for consecutive and interrupted intervals within each phase, and linear regression slopes (%/day) were calculated. Wilcoxon signed-rank tests compared slope distributions between
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