S269
Clinical - Breast
ESTRO 2026
Keywords: Breath-Hold, Cognitive Engagement
Digital Poster Highlight 2235 Toxicity and cosmetic outcomes of ultra- hypofractionated whole-breast irradiation with simultaneous integrated boost after breast- conserving surgery Emilie Natier 1 , Felipe Restini 1 , Tomas De Souza 1 , Nabia Irfan 1 , Christine Lambert 1 , Marc David 1 , Valerie Panet- Raymond 1 , Carol Oliveira 1 , Jasmine Samadi 2 , Alim Amir Amadou 3 , Tarek Hijal 1 1 Division of Radiation Oncology, McGill University Health Centre, Montreal, Canada. 2 Faculty of Science, McGill University, Montreal, Canada. 3 Faculty of Medicine, McGill University, Montreal, Canada Purpose/Objective: In early-stage breast cancer, whole-breast irradiation (WBI) improves locoregional control after breast conserving surgery (BCS)1. A 5-fraction, one-week schedule has been proven safe and non-inferior to the conventional 15-fraction regimen2, and is now established as standard of care in many countries. While a boost to the tumour bed enhances local control, it may worsen cosmetic outcomes3. Moreover, adding sequential boost can offset the time-saving benefits of ultrahypofractionation. Simultaneous integrated boost (SIB) has demonstrated low rates of adverse events and excellent cosmetic results in moderately hypofractionated settings4. However, evidence on SIB in ultrahypofractionation remains limited5. We report our experience with a 5-fraction regimen and SIB to the tumor bed. Material/Methods: We established a prospective registry of patients treated with 26 Gy in 5 fractions to the whole breast with an SIB to the tumor bed at the McGill University Health Centre. Patients are followed annually and side-effects, cosmetic and oncologic outcomes are reported in the registry. Results: A total of 198 women treated between September 2023 and September 2025 were included (median age 65, range 40–88) in this analysis. All patients had stage cT1-2N0-1 disease and were treated with BCS. Lymph node assessment was performed in 142 patients (71.7%). Neoadjuvant systemic therapy was given in 14.6%, and adjuvant systemic treatment in 47.5%, mainly endocrine therapy (70.2%). All patients received WBI 26 Gy/5 fractions with SIB to 30 Gy (98%) or 31 Gy (2%). At a median follow-up of 120 days, no grade ≥ 3 toxicity was observed. Acute side effects, measured up to 4 months post-RT, included hyperpigmentation in 45.8% of patients, grade 1 dermatitis in 15.7%, breast pain in 20.9% and breast edema in 2%. One patient
The results of the Mixed Models used to analyse these 2 groups are shown in Figure 2.
Volunteers achieved significantly longer L-DIBH times compared to patients. L-DIBH duration increases within sessions as well as between sessions, indicating a learning effect. Consecutive L-DIBHs show the greatest improvement. The mental exercise increased the mean L-DIBH duration in the total group by 14.3s (CI:7.8– 20.9) and in the patient subgroup by 18.8s (CI:10.3s – 27.4s). This effect exceeds the effect of the learning curve of a single session. Age, BMI, and weekly sport hours showed no association with DIBH duration in univariate or multivariable models.Most subjects (64%) preferred performing the mental exercise. Side effects of the supported L-DIBH were a dry mouth, dizziness and/or cough, but only reported as mild and quickly subsiding. Conclusion: A simple mental exercise is an effective way to increase the breath-hold duration when using a voluntary L-DIBH. As the effect of this exercise exceeds the intersession learning curve, it could be a time- and resource-efficient alternative to a pre-treatment practice session. References: (1) Vakaet, V., Van Hulle, H., Schoepen, M., Van Caelenberg, E., Van Greveling, A., Holvoet, J.,…Veldeman, (2021). Prolonging deep inspiration breath-hold time to 3 min during radiotherapy, a simple solution. Clin Transl Radiat Oncol, 28, 10-16. https://doi.org/10.1016/j.ctro.2021.02.007
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