ESTRO 2025 - Abstract Book

S2730

Physics - Dose prediction, optimisation and applications of photon and electron planning

ESTRO 2025

Conclusion: To our knowledge, this is the first large clinical study directly comparing VMAT and 3DCRT for breast cancer patients. The significant reduction in treatment time with VMAT, especially in patients requiring longer treatments, improves patient comfort and treatment precision. Importantly, this study demonstrates that VMAT can be performed without the increased low-dose bath commonly associated with the technique.

Keywords: VMAT, Lymph Node Coverage, clinical data

References: 1. Thorsen, L.B.J., J. Overgaard et al. "Internal Mammary Node Irradiation in Patients With Node-Positive Early Breast Cancer: Fifteen-Year Results From the Danish Breast Cancer Group Internal Mammary Node Study." *J Clin Oncol*, 2022. https://doi.org/10.1200/JCO.22.00044. 2. Engstrøm, K.H., C. Brink, M.H. Nielsen, et al. "Automatic Treatment Planning of VMAT for Left-Sided Breast Cancer with Lymph Nodes." *Acta Oncol* 60, no. 11 (2021): 1425–31. https://doi.org/10.1080/0284186X.2021.1983209. 3. Offersen, B.V., L.J. Boersma, C. Kirkove, et al. "ESTRO Guideline on Target Volume Delineation for Elective Radiation Therapy of Early Stage Breast Cancer." *Radiother Oncol* 114, no. 1 (2015): 3–10. https://doi.org/10.1016/j.radonc.2014.11.030.

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Digital Poster Performance based dosimetric limits for treatment plans of patients with prostate cancer: from conservative protocols to evidence-based constraints. Carl Rowbottom Physics Department, Clatterbridge Cancer Centre, Liverpool, United Kingdom. Physics Department, University of Liverpool, Liverpool, United Kingdom Purpose/Objective: For safety reasons, radiotherapy centres develop detailed site-specific protocols for the planning of patients. These protocols usually include dosimetric constraints expected to be met as a surrogate for acceptable plan quality. Constraints are often set conservatively taking into account patient variations and the desire to minimise protocol violations. A previous multicentre study of head-and-neck patients highlighted that real-world treated dosimetric values were substantially less than the institutional or literature-based constraints for some structures 1 . The aim of this work was to investigate the real-world achievable dosimetric values for patients with prostate cancer planned in our institution. Rectum and bladder were considered as the initial two major organs-at-risk (OARs) for the investigation. Material/Methods: Treatment plans of 500 patients with cancer of the prostate were retrospectively audited to establish performance based limits from real-world data. All plans were prescribed 60Gy/20#s and planned with a VMAT technique according to a locally defined protocol. The protocol includes appropriate mandatory, recommended and desirable volume constraints for specific dose levels. All plans are expected to achieve the mandatory constraints, with decreasing numbers of patient plans achieving the increasingly stringent recommended and desirable constraints. The 99.9% and 95% upper confidence limits were considered as appropriate performance-based mandatory and recommended volume limits. The median of the distribution was considered as the desirable dose-volume limit.