S2011
Physics - Dose prediction/calculation, optimisation and applications for photon and electron planning
ESTRO 2026
Digital Poster 4767
V20 (cc) skin in hypo breast radiotherapy as a predictor of toxicity: initial single-centre external validation of a NTCP model. Simone Baroni 1 , Claudio Scaffidi 1 , Nicola Padula 2 , Rachele Petrucci 1 , Anna Sardo 2 , Francesco Lucio 2 , Alessia Reali 1 1 SSD Radiotherapy, ASLCN2-Michele & Pietro Ferrero Hospital, Verduno, Italy. 2 SSD Medical Physics, ASLCN2-Michele & Pietro Ferrero Hospital, Verduno, Italy Purpose/Objective: Hypofractionated breast radiotherapy is now recognised as the new standard of care. Recently, Cicchetti et al. proposed the value of v20 skin (cc) as an independent predictor of acute and late skin toxicity, independent of other variables. Retrospective analysis of our centre's population as preliminary external validation. Material/Methods: From 2021 to 2025, 100 breast cancer patients undergoing moderately hypofractionated adjuvant radiotherapy with (33%) or without (77%) simultaneous integrated boost (SIB) on surgical bed were randomly selected for the analysis [median follow up 16 months (6-39)]. Clinical data about acute and late skin toxicity were collected according to the Common Terminology Criteria for Adverse Events (CTCAE 5.0) by radiation oncologist. The skin was contoured by artificial intelligence software (Limbus AI Contour) as a 5 mm isotropic expansion of the external contour of the CT body. Spearman's test was used for statistical correlation analysis. Results: Spearman's correlation analysis showed a positive and statistically significant relationship between the skin V20 (cc) value and both acute and late toxicities. Differently with the paper by Cicchetti et al., this analysis includes patients treated with SIB. Despite achieving a higher dose, in this analysis, V20 (cc) was found to be independent of the total dose. The logistic curves derived from the models indicate a progressive increase in the probability of ≥ G2 toxicity starting from V20 values above 250–300 cc. Conclusion: In this retrospective and preliminary investigation, V20 (cc) was found to be correlated with both acute and late toxicity, as described in the model by Cicchetti et al. In our case series, the volume cut-off in cc was
According to our institutional guidelines, only 3 out of 50 plans (6%) required psQA due to high plan complexity (mean MLC opening < 16.12 mm). Conclusion: A fully automated workflow for generating fraction- variant radiotherapy treatments within the commercial Eclipse TPS was successfully implemented and validated for bilateral head-and-neck cancer. This approach enables practical clinical adoption of fraction-variant planning, offering improved plan quality without extending treatment time. References: [1] Torelli, N., Day, M., & Unkelbach, J. (2025). Fraction- variant VMAT planning for patients with complex
gynecological and head-and-neck cancer. arXiv:2510.26563 [physics.med-phys].
https://doi.org/10.48550/arXiv.2510.26563.[2] Uher, K., Ehrbar, S., Tanadini-Lang, S., & Dal Bello, R. (2024). Reduction of patient specific quality assurance through plan complexity metrics for VMAT plans with an open-source TPS script. Zeitschrift fur medizinische Physik, 34(4), 555–564. https://doi.org/10.1016/j.zemedi.2023.02.003. Keywords: fraction-variant planning, head-and-neck cancer
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