S2790
RTT - RTT contouring, target definition, and treatment planning
ESTRO 2026
internal mammary chain irradiation, although a pulmonary effect was also observed on the right side. These findings reinforce the importance of systematic DIBH implementation for left-sided breast
irradiation of the whole breast or thoracic wall, medial supraclavicular lymph nodes, and internal mammary chain, comparing the left and right sides. Material/Methods: We included breast cancer patients treated with whole-breast or thoracic-wall, medial supraclavicular lymph-node, and internal mammary chain irradiation in our department between January 2022 and October 2025, with a dose of 40Gy/15F/3wk, or with an integrated boost delivering 40/48Gy/15F/3wk. For normality assessment, the Kolmogorov–Smirnov test was applied to confirm that all data were normally distributed, and an independent-samples t-test (p<0.05) was used to compare differences between groups. The mean dose (Dmean) to the heart and lung, as well as heart V17, V22 and lung V17, were compared between DIBH and free-breathing (FB) groups using the non-parametric Mann–Whitney U test. Statistical significance was set at p<0.05. Results: A total of 61 patients were analysed: 34 treated on the right side (19 with DIBH and 15 with FB) and 27 on the left side (21 with DIBH and 6 with FB). Significant differences were mainly observed on the left side, particularly in cardiac parameters. The heart Dmean was significantly reduced with DIBH compared with FB (6.62±2.67Gy vs 9.50±2.66Gy; U=24.00, p=0.025).
radiotherapy. References:
1.Wang SJ, Li X, Zhang Y, et al. Dosimetric benefit and clinical feasibility of deep inspiration breath hold in postoperative radiotherapy for left-sided breast cancer. Scientific Reports. 2024;14:75560.2.Völk F, Söhn M, Duma M, et al. Regional nodal irradiation in breast cancer patients: Effects of deep inspiration breath hold on the internal mammary chain location. Radiotherapy and Oncology. 2023;190:109926.3.Chen M, Zang S, Yu H, Ning L, Huang H, Bu L, Ge J, Xu M, Tang Q, Zhao F, Yao G, Yan S. Immobilization-assisted abdominal deep inspiration breath-hold in post- mastectomy radiotherapy of left-sided breast cancer with internal mammary chain coverage. Quant Imaging Med Surg. 2021;11(7):3314-3326. Keywords: Breast radiotherapy, DIBH, Internal mammary chain Digital Poster Highlight 3303 External validation of a deep-learning planning model for rectal cancer radiotherapy Denise le Noble 1 , Mirjam Mast 1 , Laura Bogers 2 , Marieke van Dalum 1 , Saskia van Geen 1 , Ellen Kerkhof 3 , Jean-Paul Kleijnen 2 , Barbara Rijksen 1 1 Radiotherapy, Haaglanden Medical Center, The Hague, Netherlands. 2 Medical Physics, Haaglanden Medical Center, The Hague, Netherlands. 3 Medical Physics, Leiden University Medical Center, Leiden, Netherlands Purpose/Objective: Previous studies have shown that Deep Learning (DL) techniques can improve dose distribution in radiotherapy treatment planning. The current DL- planning implementation process in RayStation involves adapting a general DL dose prediction model to specific hospital preferences. This model-adaptation process is iterative and can take up to several months. Model implementation could be accelerated by utilizing an externally optimized DL model. This study investigates the feasibility of using an externally customized model (developed and optimized at another hospital in our region) in our clinical practice. The aim of this study is to compare the target coverage and Organ-at-Risk sparing of three treatment plans in patients treated for rectal carcinoma. Material/Methods: This retrospective analysis included anonymized data from 10 patients with rectal cancer using a schedule of
Similarly, both heart V17 (8.22±6.16Gy vs 14.05±6.28Gy; U=28.00, p=0.044) and V22
(3.72±3.11Gy vs 20.23±29.82Gy; U=18.00, p=0.009) were significantly lower with DIBH. A statistically significant reduction was also found in the lung Dmean for the right side (10.99±3.02Gy vs 12.86±2.54Gy; U=84.50, p=0.046) (Fig.1). No statistically significant differences were observed in cardiac doses for right-sided treatments.
Conclusion: The dosimetric benefit of DIBH is predominantly cardiac and more pronounced in left-sided breast radiotherapy involving medial supraclavicular and
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