S239
Clinical - Breast
ESTRO 2026
Digital Poster 1396
dataset.
Left-Sided Breast Radiotherapy: Is DIBH Ever Necessary? A Feasibility Study of VMAT-Based Approaches Paolo Ferrari 1 , Said Bou Selman 2 , Michela Rosa 2 , Paola Orru 2 , Martin Maffei 2 1 Health Physics, Provincial Hospital of Bolzano (SABES- ASDAA), Bolzano, Italy. 2 Department of Radiotherapy, Provincial Hospital of Bolzano (SABES-ASDAA), Bolzano, Italy Purpose/Objective: Advances in radiotherapy technology have enabled increasingly conformal and efficient breast cancer treatments. For left-sided breast irradiation, 3D conformal radiotherapy (3D-CRT) with Deep Inspiration Breath Hold (DIBH) remains the reference standard to reduce doses to organs at risk (OARs). However, DIBH may induce patient discomfort, prolong treatment sessions, and complicate workflow for both patients and clinical staff. This feasibility study aimed to evaluate whether DIBH remains essential in the era of modern planning and delivery techniques. To this end, dosimetric outcomes of 3D-CRT with sequential photon boost in DIBH (DIBH+Boost) were compared with Volumetric Modulated Arc Therapy (VMAT) using a Simultaneous Integrated Boost (SIB), delivered both in free breathing and in breath-hold
Figure 1. Individual risk prediction
Figure 2. Explainable AI module Conclusion:
Using a systematic co-design framework with all involved stakeholders, we developed an application that communicates the AI-predicted risk of developing arm lymphedema following regional nodal irradiation in a clear and transparent manner. Reflecting the requirements identified by end-users, the individual predicted risk is presented in multiple formats and clearly explains the AI model’s training process and underlying dataset. Questionnaires on the explainable AI module demonstrated its ease of interpretation and greater usefulness compared with the raw model output, which was challenging for non-experts. The application is being used and will be validated in the PRE-ACT-01 clinical investigation. References: This work was conducted in the context of the Horizon Europe project PRE-ACT (https://preact- horizoneurope.eu/). It was supported by the European Commission through the Horizon Europe Program (Grant Agreement number 101057746), by the Swiss State Secretariat for Education, Research and Innovation (SERI) under contract number 22 00058, and by the UK government (Innovate UK application number 10061955).We thank the collaborating patient associations:1. Breast Cancer Now. https://breastcancernow.org/2. Association Ruban Rose. http://cancerdusein.org/3. Vivre Comme Avant.https://www.vivrecommeavant.fr/4. Patients en Réseau. https://monreseaucancer.org/5. Borstkanker Vereniging Nederland. https://www.borstkanker.nl Keywords: Co-design, Explainable AI, Breast cancer
conditions (SIB-BH). Material/Methods:
A retrospective analysis was performed on 15 patients with left-sided breast cancer previously treated with 3D-CRT in DIBH. 3D-CRT plans used tangential fields complemented by smaller subfields to improve dose homogeneity (40.05 Gy in 15 fractions), followed by four photon boost fields delivering 10 Gy in 5 fractions. VMAT SIB and SIB-BH plans were generated using two partial arcs prescribing 40.05 Gy to the whole breast and 48 Gy in 15 fractions to the tumor bed. All plans were normalized for PTV coverage. Equivalent doses at 2 Gy ( α / β = 3 for OARs, 10 for PTVs) were computed for direct comparison. Doses to OARs and PTVs were recorded, and conformity indices assessed. The Shapiro–Wilk test was applied to evaluate normality. For normally distributed data, paired t-tests were used; otherwise, the Wilcoxon test assessed statistical significance. Results: Compared with SIB and SIB-BH, DIBH+Boost significantly reduced Breast-R (Dmean and Dmax) and Lung-R doses. Heart dose did not differ between SIB and SIB-BH, although both achieved lower values than DIBH+Boost. SIB significantly reduced Lung-L (Dmax), Breast-R (Dmean, V2), and D110 of PTV1 compared with SIB-BH. Conversely, SIB-BH provided improved target coverage for both PTV1 and PTV2, confirmed by
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