ESTRO 2025 - Abstract Book

S517

Clinical - Breast

ESTRO 2025

Results: A total of 76 patients were included. The left/right ratio was 2.08. Fifty-three percent of patients underwent breast conserving surgery and 47% had radical mastectomy. Regional lymph nodes were irradiated for 61.8% of patients, including the internal mammary chain in 23.6% of cases. Doses to the lung showed a large interpatient variability, with Dmean Lung ranging from 2Gy to 19.2Gy, V17Gy ranging from 2.3% to 31% and V28.5Gy ranging from 0.32 to 29.57%. No significant association was found between CTVvol and doses to the ipsilateral lung. The CTVth was significantly correlated with V17Gy and V28.5Gy to the lung (Pearson coefficient = 0.4 and 0.5 and r² coefficient =0.16 and 0.25, respectively. Lung-dependant anatomy metrics had a significant predictive value of dose distribution to the lung (r² coefficient ranged from 0.5 to 0.7, all p <0.01). The CLD had the strongest predictive value for lung doses: For each 5mm increase in CLD, Dmean lung increased by 0.7Gy, V17Gy increased by 2% and V28.5Gy by 1%. Conclusion: This study showed a large interpatient variability of lung doses among breast cancer patients, primarily driven by lung-dependent anatomical factors, with CLD being the strongest predictor. These findings could be used to easily select patients with unfavourable thoracic anatomy who would benefit the most from advanced lung sparing RT techniques.

Keywords: Lung dose; anatomic predictor; breast radiotherapy

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Digital Poster Is there a difference in the breast implant loss rate between 3D radiotherapy, IMRT, or VMAT? Dayane Innocente Souza 1 , Danilo Nascimento Salviano Gomes 2 , Laura Ercolin 2 , Wanessa Fernanda Altei 1 , Enrico Martins Simoes 1 , Pedro Alves do Vale Pereira 1 , Alexandre Arthur Jacinto 1 , Barbara Alicja Jereczek-Fossa 3 , Marcos Duarte de Mattos 1 1 Radiotherapy, Hospital de Câncer de Barretos, Barretos, Brazil. 2 Radiotherapy, Hospital das Clínicas da Faculdade de Medicina de Ribeirão Preto, Ribeirão Preto, Brazil. 3 Radiotherapy, Istituto Europeo di Oncologia, Milan, Italy Purpose/Objective: To assess whether Intensity-Modulated Radiation Therapy (IMRT), Volumetric Modulated Arc Therapy (VMAT), or 3D radiotherapy influences breast implant loss, identifying potential risk factors contributing to breast implant loss and performing a dosimetric analysis to indicate predictive factors for implant loss.