ESTRO 2025 - Abstract Book

S4403

RTT - Treatment planning, OAR and target definitions

ESTRO 2025

± SD (quantitative) and frequencies (qualitative). Mixed-model ANOVA compared tumor laterality, DIBH vs. FB, and their interaction (p<0.05).

Results: Seventy patients (52.9% left breast, 47.1% right breast), mean age 57.9±11.4, were included. Dosimetric differences (DIBH-FB) were: PTV V95: 0.02±0.36; PTV V105: 0.25±1.00; heart V5: -2.53±4.09; heart V25: -0.19±1.63; heart mean dose: -0.10±0.21; lung V30: -0.43±1.69; lung mean dose: -0.09±0.43. All plans met dose constraints. No significant effects of DIBH or side were seen for target volumes (p > .05). For heart V5, tumor side (F(1,68)=33.2, p<.001, hp²=0.07) and DIBH (F(1,68)=26.2, p<.001, hp²=0.28) had significant effects, with no interaction. Heart mean dose showed significant effects for side (F(1,68)=16.9, p<.001, hp²=0.20), DIBH (F(1,68)=18.7, p<.001, hp²=0.22), and interaction (F(1,68)=17.7, p<.001, hp²=0.21). Heart V25 showed no side/DIBH effects but had a significant interaction (F(1,68)=4.45, p=.039, hp²=0.061). Lung V30 showed a DIBH effect (F(1,68)=4.55, p=.037, hp²=0.063), with no side or interaction effects. Conclusion: The study concludes that while DIBH significantly reduces radiation exposure to vital organs, such as the heart and lungs, compared to free breathing (FB), these reductions do not lead to clinically significant differences in complication risks. Both methods are safe and effective for Partial Breast Irradiation (PBI). However, FB is a simpler and faster option, suitable for patients who struggle with DIBH. Therefore, FB is a valuable alternative when DIBH is not feasible, ensuring adequate tumor control and patient safety. References: 1. Whelan, T., & Pignol, J. P. (2020). Long-term results of hypofractionated radiotherapy for breast cancer: The FAST Forward trial. Lancet , 395 (10237), 1981–1992. https://doi.org/10.1016/S0140-6736(20)31051-5 2. Decker, R. H., & Lentz, J. M. (2016). Partial breast irradiation: A review of techniques and clinical results. American Journal of Clinical Oncology , 39 (3), 305–310. https://doi.org/10.1097/COC.0000000000000146 3. Kelsey, C. R., & Rineer, J. (2017). Deep inspiration breath hold in breast cancer radiotherapy: A review. Radiation Oncology , 12 (1), 1–11. https://doi.org/10.1186/s13014-017-0846-3 Keywords: Deep-Inspiratory-Breath-Hold , Free-Breathing,PBI) Proffered Paper Evaluation of unsupervised use of AI-generated structures in CBCT-guided online adaptive radiotherapy for patients with urinary bladder cancer Lisette J. Sandt 1 , Raúl Argota-Pérez 1 , Katrine Storm 1 , Lina M. Åström 1 , Claus P. Behrens 1,2 , Patrik Sibolt 1 1 Department of Oncology, Copenhagen University Hospital – Herlev and Gentofte, Copenhagen, Denmark. 2 Department of Health Technology, Technical University of Denmark, Roskilde,, Denmark Purpose/Objective: Purpose/objective: CBCT-guided online adaptive radiotherapy (oART) for urinary bladder cancer has demonstrated promising results in reducing treatment margins, thereby minimizing dose to surrounding healthy tissue. However, the oART process can be time-consuming due to AI-generated structure edits, and with inter- and intra-fractional variations posing challenges. Unsupervised AI-generated structures might enhance treatment efficiency and consistency. This study aimed to evaluate the impact of unsupervised AI-generated structures on dose to targets and organs at risk, and the adaptive procedure duration for patients with urinary bladder cancer. 4282