S1912
Physics - Dose prediction/calculation, optimisation and applications for photon and electron planning
ESTRO 2026
recommendations for robust IMC radiotherapy. Literature reviews assessed expected variations between planning and treatment conditions, including set - up uncertainties, intra - fraction motion, anatomical changes, and machine calibration errors. Consensus definitions of robustness were established, and planning principles for photon radiotherapy were derived using modern treatment planning systems. Guidance was informed by UK trial protocols and ESTRO contouring consensus2. Results: Robustness was defined as maintaining target coverage and organ - at - risk (OAR) sparing despite deviations from planning conditions. Anticipated variations included set - up errors, respiratory motion, anatomical changes (e.g. oedema), and machine factors. Recommendations emphasise the value of breath - hold techniques, ESTRO - aligned contouring, and strict dose constraints for heart, lungs, contralateral breast, and oesophagus. AI auto - contouring tools are encouraged for efficiency and consistency, with clinical oversight essential.Planning approaches ranged from wide tangents to inverse - planned IMRT/VMAT and hybrid techniques, with highly conformal methods achieving superior coverage and OAR sparing. Key considerations include maintaining skin flash, managing PTVs extending into lung, and limiting plan complexity to preserve robustness. System - specific guidance and strategies for complexity control are provided. Robustness evaluation methods include simulated isocentre shifts, density overrides, and integrated plan - complexity checks. Conclusion: These recommendations offer practical guidance for UK centres implementing IMC irradiation. By auditing local set - up performance, applying appropriate margins, and integrating robust planning strategies, centres can deliver efficient, high - quality IMC radiotherapy that achieves target coverage while minimising OAR risk. This guidance supports consistent national practice and underpins ongoing trials, enabling safe and standardised adoption across the UK. References: (1) Royal College of Radiologists. (2016). Postoperative radiotherapy for breast cancer: UK consensus statements. (2) Offersen, B. V, Boersma, L. J., Kirkove, C., Hol, S., Aznar, M. C., Biete Sola, A., Kirova, Y. M., Pignol, J.-P., Remouchamps, V., Verhoeven, K., Weltens, C., Arenas, M., Gabrys, D., Kopek, N., Krause, M., Lundstedt, D., Marinko, T., Montero, A., Yarnold, J., & Poortmans, P. (2015). ESTRO consensus guideline on target volume delineation for elective radiation therapy of early stage breast cancer. Radiotherapy and Oncology, 114(1), 3–10 Keywords: Robustness, IMC, guidance
dose, should be used in the conversion to guarantee consistent target BED. This would be especially important for proton therapy. References: de Jong, E.E.C., Guckenberger, M., Andratschke, N., Dieckmann, K., Hoogeman, M.S., Milder, M., Møller, D.S., Nyeng, T.B., Tanadini-Lang, S., Lartigau, E., Lacornerie, T., Senan, S., Verbakel, W., Verellen, D., De Kerf, G., Hurkmans, C., 2020. Variation in current prescription practice of stereotactic body radiotherapy for peripherally located early stage non-small cell lung cancer: Recommendations for prescribing and recording according to the ACROP guideline and ICRU report 91. Radiotherapy and Oncology 142, 217– 223. https://doi.org/10.1016/j.radonc.2019.11.001 Keywords: BED, SBRT, Lung cancer Guidance for robust planning and delivery of internal mammary chain irradiation in breast radiotherapy Lakshmi Balakrishnan 1 , Andrew Bird 2 , Ruth Colgan 3 , Jim Daniel 4 , Jonathan Entwisle 5 , Sarah Gulliford 6 , Katie Long 7 , Becky Milliner 8 , Sarah Muscat 9 1 Oncology, University Hospitals of Leicester NHS Trust, Leicester, United Kingdom. 2 Radiotherapy Physics, Worcestershire Acute Hospital NHS Trust, Worcester, United Kingdom. 3 Joint Department of Physics, The Royal Marsden NHS Foundation Trust, Sutton, United Kingdom. 4 Radiotherapy Physics, South Tees Hospitals NHS Foundation, Middlesbrough, United Kingdom. 5 Medical Physics, Leeds Teaching Hospitals Trust, Leeds, United Kingdom. 6 Medical Physics, University College London Hospitals NHS Foundation Trust, London, United Kingdom. 7 Medical Physics, Royal Surrey County Hospital NHS Foundation Trust, Guildford, United Kingdom. 8 Radiotherapy, Gloucestershire Hospitals NHS Foundation Trust, Cheltenham, United Kingdom. 9 Medical Physics, Portsmouth Hospitals University NHS Trust, Portsmouth, United Kingdom Purpose/Objective: In 2016, the UK Royal College of Radiologists (RCR) recommended internal mammary chain (IMC) irradiation for selected breast cancer cohorts, stressing techniques that minimise cardiac and pulmonary dose1. Since then, UK centres have adopted increasingly complex modulated approaches, but significant variation persists. This highlights the need for consensus guidance on robust planning and delivery. Digital Poster 2977
Material/Methods: A multidisciplinary Task and Finish group developed
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