ESTRO 2025 - Abstract Book

S2939

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

ESTRO 2025

References: 1.

Raphael MJ, Saskin R, Singh S. Association between waiting time for radiotherapy after surgery for early-stage breast cancer and survival outcomes in Ontario: a population-based outcomes study. Current Oncology. 1 mai 2020;27(2):e216. 2. Caponio R, Ciliberti MP, Graziano G, Necchia R, Scognamillo G, Pascali A, et al. Waiting time for radiation therapy after breast-conserving surgery in early breast cancer: a retrospective analysis of local relapse and distant metastases in 615 patients. European Journal of Medical Research. 11 août 2016;21(1):32.

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Digital Poster Estimation of mean heart dose using maximum heart depth in a large retrospective sample of left breast cancer patients planned with wide tangents Ian Gleeson 1 , Charlotte E Coles 2 , Anna M Kirby 3 , Sairanne Wickers 4 , Rajesh Jena 5 1 Medical Physics, Cambridge University Hospitals NHS Foundation Trust, Cambridge, United Kingdom. 2 Department of Oncology, University of Cambridge, Cambridge, United Kingdom. 3 Oncology, Royal Marsden Hospital, London, United Kingdom. 4 Oncology, University College London Hospital, London, United Kingdom. 5 Oncology, Cambridge University Hospitals NHS Foundation Trust, Cambridge, United Kingdom Purpose/Objective: Minimising mean heart dose (MHD) is important in left-sided breast radiotherapy, as even a 1 Gy increase in MHD raises the risk of major coronary events by about 7.4 % [1]. A straightforward tool for MHD prediction could streamline care, reduce delays, and facilitate prioritisation of heart-sparing techniques, especially in resource limited settings. While prior studies have explored predictors of MHD, they are often limited by smaller datasets, varying techniques, and compromises in target coverage [2]. This retrospective study re-planned a large cohort of left-sided IMN cases with wide tangents, prioritising target coverage and using automated data collection for large scale analysis. It offers robust insights into the relationship between maximum heart depth (max_heart_depth) and MHD. Material/Methods: A single-centre retrospective cohort of 224 breast cancer patients was re-outlined according to ESTRO guidelines and re-planned using wide tangents photons to target the breast/chest-wall, IMN, and regional nodes. Plans were created with 40 Gy in 15 fractions, prioritising target coverage during planning over organs at risk. A Raystation script recorded max_heart_depth (as previously described in [3]), mean heart dose, and the max_heart_depth position relative to the inferior extent of the IMN PTV. The relationship between MHD and max_heart_depth was evaluated using various regression models, with the highest R² model selected for leave-one-out cross-validation, yielding root mean square error (RMSE) and 90–100 % prediction intervals (PI). Results: A 5-degree polynomial achieved the best fit with an R² of 0.889, outperforming linear regression (R² 0.854), indicating a strong correlation between MHD and max_heart_depth. Cross-validation of the polynomial model yielded an RMSE of 0.97 Gy and a 90 % PI of ± 1.6 Gy. The max_heart_depth was located below the inferior border of the IMN PTV in 82.3 % of cases.