ESTRO 2025 - Abstract Book

S529

Clinical - Breast

ESTRO 2025

Conclusion: The relatively low energy of the Halcyon machine required the development of a new treatment technique for patients receiving complex breast radiotherapy. A fixed-field IMRT technique was developed which improved PTV coverage and gave similar or improved OAR doses compared to the standard tangential arrangement and whilst low dose spillage was increased, it was substantially lower than for VMAT and remained within clinically acceptable limits. The fixed-field ‘butterfly’ technique therefore allows the delivery of breast and nodal radiotherapy on the Halcyon machine and is now in routine use in our department. References: [1] Flores-Martinez, E., et al. (2019). Dosimetric study of the plan quality and dose to organs at risk on tangential breast treatments using the Halcyon linac. J Applied Clinical Medical Physics , 20 (7), 58–67. [2] Karpf, D., et al. (2019). Left breast irradiation with tangential intensity modulated radiotherapy (t-IMRT) versus tangential volumetric modulated arc therapy (t-VMAT): trade-offs between secondary cancer induction risk and optimal target coverage. Radiation Oncology , 14 , 1-11. Keywords: Butterfly Technique, Flattening-Filter-Free

[3] Racka, I., et al. (2023). Hybrid planning techniques for early-stage left-sided breast cancer: dose distribution analysis and estimation of projected secondary cancer-relative risk. Acta Oncologica , 62 (8), 932-941.

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Digital Poster Single-arm Meta-Analysis of Pre-Operative Radiotherapy in Early Breast Cancer: A Paradigm Shift? Kratika Bhatia 1 , Preetha Umesh 1 , Kundan Singh Chufal 1 , Irfan Ahmad 1 , Alexis Andrew Miller 2 , Balamrit Singh Sokhal 3 , Harsh Vyas 1 , Munish Gairola 1 1 Radiation Oncology, Rajiv Gandhi Cancer Institute & Research Centre, New Delhi, India. 2 Radiation Oncology, Illawarra Cancer Care Centre, New South Wales, Australia. 3 School of Medicine, Keele University, Staffordshire, United Kingdom Purpose/Objective: Preoperative radiotherapy (PRT) is potentially a paradigm shift in the management of early breast cancer (EBC). It aims to enhance surgical outcomes by downstaging tumors, increasing breast-conserving surgery (BCS) rates, and reducing reconstruction complications. Compared to standard postoperative RT, it could obviate the need to delay RT due to surgical wound complications and permit re-irradiation of in-breast tumor recurrences. This meta analysis of single-arm studies aimed to evaluate its effectiveness in achieving pathological complete response (pCR) and minimizing surgical morbidity. Material/Methods: A systematic search (till March 2024) across MEDLINE and PMC databases identified 1,327 studies, of which 30 met the inclusion criteria (Figure 1). Extreme hypofractionation (including SBRT) was defined as a course of RT delivered within 10 fractions, which treated the primary lesion only, whereas long-course RT (+/-sequential chemotherapy) treated the entire breast with regional nodal irradiation (often with older techniques). Analysis was performed in R v4.2.1, using the meta package.