ESTRO 2025 - Abstract Book

S556

Clinical - Breast

ESTRO 2025

Material/Methods: Data from 692 patients (pts) treated at the same Institute between 2017 and 2021 were evaluated. At that time, newer delivery techniques (VMAT, ViTAT, a variety of VMAT with extended arc blocking, and TomoDirect) were gradually introduced making available a population with patients treated during the same time period with 3d-CRT (with wedge or field-in-field manual optimization) or AT. All patients received 40Gy/15fr to the whole breast, without any boost. The choice of the technique was at discretion of the treating clinician and was mostly driven by the complexity of the anatomy and by the machine availability. Toxicity was monitored during follow-up (FU) according to the RTOG (Radiation Therapy Oncology Group) scale criteria. Patients exhibiting ≥G2 oedema within six months post-radiotherapy were classified as the ones experiencing toxicity. Differences between patient’s characteristics between the two cohorts were preliminarily assessed through Chi square or Mann-Whitney tests. The difference of oedema incidence between the two modalities was tested through Chi-square test. Results: The patients treated with 3d-CRT were 299 (43.1%) while those treated with AT were 393 (56.9%, VMAT: 242; ViTAT: 46; TomoDirect: 105): 55 pts developed 6-month G2 oedema. The patient’s characteristics (i.e.: chemotherapy, hormonal therapy, trastuzumab, breast size, obesity, diabetes, smoke, hypertension, thyroid illness) were not different between the two cohorts, excepting PTV volume; importantly, when comparing the PTV volumes between 3d-CRT and AT (Table 1), they resulted significantly (p<0.05) larger in the AT group, potentially in favor of the 3d-CRT group if considering the risk of oedema. The rate for AT was significantly lower than the rate for 3d-CRT (6.1% vs 10.4%, p=0.04).

Conclusion: The introduction of AT for whole breast irradiation was able to better spare the tissues surrounding PTV, resulting in a lower incidence of oedema at six months, an important result since acute ≥G2 toxicity is correlated with late fibrosis and atrophy (3). This finding was obtained despite the fact that patients with larger PTV (closely associated with larger breast volume) were preferentially treated with AT.

Keywords: Hypofractionated Radiotherapy, Oedema, IMRT

References: 1. Verbelen H, et al. Breast edema in breast cancer patients following breast-conserving surgery and radiotherapy: a systematic review. Breast Cancer Res Treat. 2014; 147(3): 463-71. 2. Verbelen H, et al. Breast edema, from diagnosis to treatment: state of the art. Arch Physiotherapy 2021; 11:8 3. Fodor A, et al. Toxicity of Hypofractionated Whole Breast Radiotherapy Without Boost and Timescale of Late Skin Responses in a Large Cohort of Early-Stage Breast Cancer Patients. Clin Breast Cancer 2022; 22(4):e480 e487.