S2763
RTT - RTT contouring, target definition, and treatment planning
ESTRO 2026
failed to meet all three constraints, 33 failed only the cardiac constraints, and 51 failed only the pulmonary constraint.When comparing techniques, DIBH was associated with a significant improvement in the heart V5% parameter, while no significant advantage was observed for the remaining dosimetric criteria.CTV volume was significantly higher in the MH group (n=150, 734.8 ± 326.7 cc) compared with the UHF group (n=150, 589.2 ± 258.3 cc; p < 0.01), with no correlation between CTV volume and OAR dose parameters.The use of MH peaked in 2021 and progressively decreased through March 2025. Linear regression showed an annual reduction of approximately 12 cases/year (p = 0.047), indicating increasing adoption of UHF. Conclusion: The main limitations to UHF implementation were laterality, CTV volume, and failure to meet OAR dose constraints. When comparing FB and DIBH, only pulmonary dosimetric parameters showed statistically significant improvements with DIBH. References: 1. Brunt AM, Wheatley DA, Yarnold J, Somaiah N, Kelly S, Horan G, et al. Ten-year results of FAST: once-weekly hypofractionated whole-breast radiotherapy. Radiother Oncol. 2020;147:89–98.2. Offersen BV, Alsner J, Nielsen HM, Jakobsen EH, Nielsen M, Haarmark C, et al. Hypofractionated versus conventional breast irradiation: updated Danish Breast Cancer Group guidelines. Radiother Oncol. 2023;183:109624.3. Mast M, van Werkhoven E, Heuts EM, Myerson RJ, Reitsamer R, Poortmans P. Patient suitability and clinical considerations for partial breast irradiation in ultra-hypofractionation. Breast. 2022;61:67–74. Keywords: Radiatiotherapy, Hypofractionation, Breast Dosimetric comparison between manual plans and automated plans by Raystation planning system in breast cancers Tsz Kwan Chan 1,2 , Man Cheuk Ng 3,4 1 Department of Clinical Oncology, Princess Margaret Hospital, Hong Kong, Hong Kong. 2 Department of Diagnostic Radiology and Clinical Oncology, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Pokfulam, Hong Kong. 3 Department of Diagnostic Radiology and Clinical Oncology, Li Ka Shing Faculty of Medicine, The University of Hong Kong,, Hong Kong. 4 Oncology Centre, St. Teresa’s Hospital, Hong Kong, Hong Kong Digital Poster 388
193.3.Tonetto, F.; Magli, A.; Moretti, E.; Guerini, A.E.; Tullio, A.; Reverberi, C.; Ceschia, T.; Spiazzi, L.; Titone, F.; Prisco, A.; et al. Prostate Cancer Treatment-Related Toxicity: Comparison between 3D-Conformal Radiation Therapy (3D-CRT) and Volumetric Modulated Arc Therapy (VMAT) Techniques. J. Clin. Med. 2022, 11, 6913. Keywords: Retal Spacer, VMAT, Prostate cancer Digital Poster 375 Why Not 26 Gy? Limitations of Ultra- Hypofractionation: Insights From a Single-Center Experience Daniela Saraiva 1,2 , Fernando M. Costa 1,3 , Raquel Rocha 1 , Daniela Branco 1 , Patrícia Varzim 1 , Patrícia Peixoto 1 , Armanda Monteiro 1,3 , Gabriel Farinha 1 , Alice Alves 1,2 , Pedro Meireles 1 , Lígia Osório 1 1 Radiotherapy, ULS São João, Porto, Portugal. 2 University of Vigo, University of Vigo, Vigo, Spain. 3 Radiotherapy, E2S - Escola Superior de Saúde, Porto, Portugal Purpose/Objective: Ultra-hypofractionation (UHF), delivered as 26 Gy in 5 fractions, represents a new paradigm in breast cancer treatment. However, not all treatment plans meet the dose constraints for organs at risk (OAR), which occasionally necessitates the use of moderate hypofractionation (MH), typically 40.05 Gy in 15 fractions. The aim of this study is to analyze the limitations to UHF use by evaluating laterality, lung and heart doses, Clinical Target Volume (CTV) size, and the application of Deep Inspiration Breath Hold (DIBH). Material/Methods: A retrospective observational study was conducted, including 1330 patients eligible for UHF and treated between March 2020 and March 2025. Of these, 863 received UHF and 467 underwent MH. Among the MH group, 285 patients were excluded due to lack of available dosimetric plans and 31 due to contraindications, resulting in a total of 151 patients for analysis. The following dose constraints were assessed: Lung V30% ≤ 17%, Heart V5% ≤ 25%, and Heart V25% ≤ 5%. CTV volumes were compared between MH and UHF groups, and correlations with OAR dose parameters were evaluated. Statistical analyses included Mann-Whitney, Chi-square/Fisher’s exact tests, and Pearson/Spearman correlations. Results: Among the 151 patients analyzed (106 left-sided and 45 right-sided), 71 were treated with Free Breathing (FB) and 80 with DIBH. A total of 115 plans exceeded the lung V30% constraint, 77 exceeded the heart V5%, and 90 exceeded the heart V25%. Forty-two plans
Purpose/Objective: To compare the dosimetric performance, organ-at-risk
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