S2808
RTT - RTT contouring, target definition, and treatment planning
ESTRO 2026
Material/Methods:
(DBCG IMN2): A prospective, nationwide, population- based Cohort Study. The Lancet Regional Health - Europe. 2025 Feb;49:101160. doi:10.1016/j.lanepe.2024.101160 Keywords: VMAT, Comprehensive Nodal Breast, 5Fractions
Twenty patients treated on a Varian Truebeam with three continuous VMAT arcs (220° trajectory) were retrospectively replanned. The prescribed dose was 26Gy in 5 fractions to the breast, lymph nodes, and internal mammary chain, with a simultaneous integrated boost of 28–30Gy. New arcs were segmented with optimised collimator angles tailored to each patient’s target volume. Results: Modification of VMAT arcs with tailored collimator angles significantly reduced dose to OARs without compromising target coverage. Mean dose to heart, contralateral beast and contralateral lung decreased by 6%, 2.5%, 12.63% respectively. Contralateral V10% also decreased by 24.4%. Collimator optimisation did not significantly affect ipsilateral mean or V10% dose. Split arc plans averaged 1.7 arcs versus 3 in original plans, reducing treatment time and improving patient comfort. Additionally, five shorter fields enhanced deep inspiration breath hold (DIBH) compliance. Conclusion: With recent evidence linking IMN RT to improved overall survival2, developing safe, effective delivery techniques for ultra-hypofractionated nodal RT is a key clinical focus. This approach demonstrates adapting to new data and refining strategies for comprehensive nodal breast radiotherapy. References: 1.Kim N, Chang JS, Shah C, Shin H, Keum KC, Suh C, et al. Hypofractionated volumetric - modulated arc therapy for breast cancer: A propensity - score - weighted comparison of radiation - related toxicity. International Journal of Cancer. 2021 Feb 18;149(1):149–57.2.Nielsen AW, Thorsen LBJ, Özcan D, Matthiessen LW, Maae E, Milo MLH, et al. Internal mammary node irradiation in 4541 node-positive breast cancer patients treated with newer systemic therapies and 3D-based radiotherapy
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