S1799
Physics - Dose prediction/calculation, optimisation and applications for photon and electron planning
ESTRO 2026
Digital Poster 122 Dosimetric performance of an optimized volumetric modulated arc therapy strategy in locoregional breast cancer radiotherapy Mahmoud Alfishawy, Tauseef Ali, Muhsina Vellengara, Iqbal AL Amri, Zahid Al-Mandhari, Ana Paula Galerani Lopes Radiation Oncology, Sultan Qaboos Comprehensive Cancer Care and Research Centre, University Medical City, Muscat, Oman Purpose/Objective: The use of volumetric modulated arc therapy (VMAT) in locoregional breast cancer has gained increasing adoption due to its ability to achieve highly conformal dose distributions while sparing adjacent critical structures.This study aimed to evaluate an optimized VMAT technique for locoregional breast cancer treatment, requiring regional nodal irradiation, including the internal mammary (IMN), axillary, and supraclavicular lymph nodes (Node). Material/Methods: A total of 139 patients treated between January 2024 and January 2025 were included. All patients received 40 Gy in 15 fractions, and 37 of them received a simultaneous integrated boost (SIB) to 48 Gy.Several key planning strategies and technical considerations were applied, these included the implementation of breast flash techniques to account for respiratory motion and the restriction approach of beam entry to avoid passage through the ipsilateral arm. To improve plan deliverability and reduce treatment complexity, moderate aperture shape controller settings were employed to minimize multi-leaf collimator modulation. In addition, specialized optimization structures and limited cumulative gantry rotation were incorporated to enhance plan efficiency and deliverability without compromising dosimetric quality.
Results: In patients receiving SIB, the planning target volume (PTV) coverage for boost volume at V50.4Gy (volume receiving 50.4Gy) and V45.6Gy was 5.68% and 97.45%, respectively. For remaining targets, coverage was PTV- Breast V38Gy: 97.21%, PTV-Node V38Gy: 96.96%, and PTV-IMN V34Gy: 97.25%. The corresponding mean homogeneity index (HI), conformity index (CI), and gradient index (GI) were 1.28, 0.97, and 2.57. In non- SIB cases, PTV-Breast V42.8Gy and V38Gy were 2.94% and 96.62%; PTV-Node V42.8Gy and V38Gy were 1.04% and 97.16%; and PTV-IMN V34Gy was 98.80%. The mean HI, CI, and GI were 1.10, 0.97, and 3.34, respectively.Regarding organs at risk (OAR), mean doses to the ipsilateral lung, contralateral lung, total lung, heart, and contralateral breast were 10.78 Gy, 1.96 Gy, 6.56 Gy, 3.56 Gy, and 3.18 Gy, respectively. Volume-based metrics showed heart V4Gy: 24.60%, V25Gy: 0.68%; ipsilateral lung V5Gy: 53.35%, V10Gy: 34.41%, V20Gy: 20.98%; contralateral lung V5Gy: 7.01%, V20Gy: 0.01%; and contralateral breast V5Gy: 17.45%. Conclusion: This study confirmed the clinical use of our optimized VMAT technique compared to published literature data range, which incorporated specific planning strategies for locoregionally breast cancer. The approach demonstrated highly effective target coverage across all volumes, with improvements in dose homogeneity, conformity, and sparing of organs at risk, particularly the heart and ipsilateral lung. Overall, this VMAT strategy represents a reliable and effective solution for locoregional breast cancer radiotherapy.
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