ESTRO 2025 - Abstract Book

S482

Clinical - Breast

ESTRO 2025

1 Department of Radiation Oncology, Medical University Vienna, Vienna, Austria. 2 Christian Doppler Laboratory for Image and Knowledge Driven Precision Radiation Oncology, Medical University Vienna, Vienna, Austria

Purpose/Objective: Adjuvant local breast cancer radiotherapy was shown to be oncologically safe and effective independent from the treatment regimen (26Gy/5fx or 40Gy/15fx) [1,2] with only mild symptoms, as confirmed by PROMs data on skin and chest wall-related toxicities [3,4]. This study evaluated the association between skin dose-volume parameters and the risk of patient-reported radiation-induced toxicities. Material/Methods: We analyzed PRO-CTCAE data from 374 breast cancer patients (26 Gy/5fx: n=148, 40Gy/15fx: n=226) at baseline and at 3, 6, 9, 12 and 24 months follow-up (IRB: 2184/2019). For the majority of patients, the whole breast was irradiated, while 22%received partial breast irradiations. These data were collected using our in-house developed ePROM application. A pipeline in RayStation (RaySearch, Sweden) interfaced with the MOSAIQ R&V system (Elekta, Sweden) to extract delivered dose-volume data, i.e., V35Gy _EQD2 and V5Gy _EQD2 for the skin (thickness 4mm). We used univariate Cox proportional hazards regression to model time to onset for itching, radiation skin reaction, and breast swelling/tenderness, with the skin dose-volume parameters as variables (α=0.05). Time-to-event was measured from radiotherapy start to a worsening of ≥2 in any endpoint, with censoring at the last follow-up if no event occurred. Patients were excluded if they started radiotherapy with grade 3 or higher symptoms at baseline. Results: The mean irradiated skin volumes were V35Gy _EQD2 = 136.1 ± 58.7 cm³ and V5Gy _EQD2 = 257.5 ± 103.2 cm³. Cox proportional hazards analysis revealed that a larger high-dose skin volume (V35Gy_ EQD2 ) was significantly associated with an increased risk of developing late toxicities, specifically radiation skin reaction (HR per cm³ = 1.01, p < 0.001) and breast swelling/tenderness (HR per cm³ = 1.01, p = 0.036). This translates to approximately a 78% increase in risk for every one standard deviation (58.7 cm³) increase in V35Gy _EQD2 . The low-dose skin volume (V5Gy _EQD2 ) was not significantly associated with an increased risk of radiation skin reaction (p = 0.100) or swelling/tenderness (p = 0.399). There was no significant association between low-dose or high-dose skin volumes and itching (p = 0.233 and p = 0.408, respectively). Conclusion: High-dose skin volumes were associated with late radiation-induced skin reactions after breast cancer radiotherapy. These findings highlight the potential to optimize treatment in terms of further individualization by reducing treatment volumes where it is oncologically safe.

Keywords: PROM, breast cancer, outcome models

References: [1]

Brunt et al. doi :10.1016/S0140-6736(20)30932-6. Brunt et al. doi: 10.1016/j.radonc.2016.02.027. Lapen et al. doi: 10.1016/j.adro.2023.101263. Batenburg et al. doi: 10.1016/j.ijrobp.2022.11.008.

[2] [3] [4]

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Digital Poster Dosimetric comparison of deep inspiration breath hold versus free breathing techniques in adjuvant radiotherapy to left-sided breast cancer patients Soumita Majumdar 1 , Anupam Datta 1 , Partha Sen 1 , Jyotirup Goswami 1 , Avishek Pal 2 , Soumik Gain 2