S1803
Physics - Dose prediction/calculation, optimisation and applications for photon and electron planning
ESTRO 2026
Conclusion: A TMJ-sparing tomotherapy plan can significantly decrease the radiation dose to TMJs. This approach lowers the predicted risk of radiation-induced trismus without compromising target coverage or increasing doses to adjacent critical organs. A mean dose of 18 Gy to the TMJ is recommended as a feasible strategy for reducing NPC late toxicities and improving post- treatment quality of life for the NPC patients. References: Morimoto, M., et al., Development of Normal Tissue Complication Probability Model for Trismus in Head and Neck Cancer Patients Treated With Radiotherapy: The Role of Dosimetric and Clinical Factors. Anticancer Research, 2019. 39(12): p. 6787-6798.Faravel, K., et al., Trismus Occurrence and Link With Radiotherapy Doses in Head and Neck Cancer Patients Treated With Chemoradiotherapy. Integrative Cancer Therapies, 2023. 22: p. 15347354221147283.Wu, V.W., M.T. Ying, and D.L. Kwong, A study on the post-radiotherapy changes of temporomandibular joint in nasopharyngeal carcinoma patients. Br J Radiol, 2017. 90(1080): p. 20170375. Keywords: nasopharyngeal carcinoma, tomotherapy, TMJ sparing Early and late pulmonary function changes after hypofractionated breast radiotherapy: prospective evaluation and dosimetric correlations Raouia Ben Amor 1,2 , Saloua Jameleddine 3,2 , Dorra Herch 4 , Zeineb Naimi 1,2 , Rihab Haddad 1 , Ghada Bouguerra 1 , Awatef Hamdoun 1 , Lotfi Kochbati 1,2 1 Radiation Oncology, Abderrahmen Mami Hospital, Ariana, Tunisia. 2 Faculty of Medicine of Tunis, Tunis El Manar University, Tunis, Tunisia. 3 Pulmonary Function Laboratory, Abderrahmen Mami Hospital, Ariana, Tunisia. 4 Radiation Oncology, Habib Bourguiba Hospital, Sfax, Tunisia Digital Poster 453 Purpose/Objective: Adjuvant breast radiotherapy exposes portions of the lung to ionizing radiation, potentially causing functional impairment. While hypofractionated regimens are increasingly standard due to their efficacy and safety, their impact on pulmonary function is poorly characterized. This prospective study aimed to assess changes in lung function following hypofractionated breast radiotherapy and explore correlations with lung dosimetry. Material/Methods: Fifty-six consecutive breast cancer patients treated between 2020 and 2022 with 3D hypofractionated radiotherapy (40.05 Gy in 15 fractions) were prospectively evaluated. Left- and right-sided tumors
were equally represented, with 28 patients in each group; 42 patients received locoregional radiotherapy, while 14 were treated to the breast alone. Pulmonary function tests, including FEV1, FVC, FEV1/FVC ratio, and DLCO, were performed at baseline, 3 months, and 12 months post-treatment. Lung dosimetric parameters, including mean dose and volume-based metrics (V4, V6, V17, V28.5), were derived from treatment planning data. Changes in pulmonary function over time were assessed using the Friedman test for repeated measures. Spearman’s rank correlation was used to evaluate associations between pulmonary function changes and lung dosimetric parameters. Results: Fifty-two patients were evaluable. At baseline and throughout follow-up, none of the patients presented with respiratory symptoms. At 3 months, mean Δ FEV1 was -0.047 ± 0.271 L, Δ FVC -0.048 ± 0.332 L, and Δ DLCO +0.159 ± 2.187, indicating minimal early changes. At 12 months, mean Δ FEV1 was -0.110 ± 0.263 L, Δ FVC -0.128 ± 0.341 L, and Δ DLCO -0.137 ± 3.206, reflecting slight long-term decreases. Changes between 3 and 12 months ( Δ FEV1 = -0.064 ± 0.222 L; Δ FVC = -0.080 ± 0.273 L; Δ DLCO = -0.296 ± 1.696) suggest progressive but modest decline.(Table1) There were no clinical symptoms correlated to these changes during the follow-up period.
Correlation analysis revealed a significant inverse association between Δ FEV1 at 3 months and ipsilateral lung V4 (r = -0.278, p = 0.048). Other correlations with low- and intermediate-dose parameters (V8, V17, V28.5, mean lung dose) were negative but non- significant. Δ FVC and Δ DLCO changes were not significantly associated with dosimetric parameters. (Table 1) Boxplots highlighted the overall stability of FEV1, FVC, and DLCO, while scatterplots illustrated early FEV1 decline in relation to low-dose lung exposure.(Figure1)
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