ESTRO 2025 - Abstract Book

S1849

Clinical – Upper GI

ESTRO 2025

heart dose often increases lung dose, prompting varied approaches in treatment plan optimisation. This study aims to provide insights into practice variation in optimisation approaches among centres, specifically regarding heart and lung dose, and evaluating their impact on target coverage robustness. Material/Methods: For this planning study, three patients with EC were retrospectively selected, with various tumour locations, target motion, target volumes and anatomical changes during treatment. CT images and structure sets (including targets and OARs) were shared with 13 Dutch radiotherapy centres, which created a photon treatment plan according to their clinical standards for all three patients. Dose distributions were compared in terms of target and OARs dose. By recalculation of the treatment plan on repeated CTs, robustness was analysed. The dose was warped by deformable image registration to the planning CT and summed to resemble the total treatment course dose. Results: All 13 centres used volumetric arc therapy (VMAT) as treatment technique with one (n=2), two (n=9) or three (n=2) arc(s) and 6 (n=8) or 10 MV (n=5). Target coverage in terms of D98 (relative dose to 98% of PTV) was on average 95.1±0.8%, while in 69% of plans D98 was >95%. Mean heart dose (MHD) and mean lung dose (MLD) of all treatment plans are shown in Figure 1. The difference between the plans with the lowest and highest MHD was 6.2 Gy (range: 6.6 Gy-12.8 Gy) for patient A, 10.0 Gy (range: 10.0-20.0 Gy) for patient B, and 13.3 Gy (range: 14.6-27.9 Gy) for patient C. On average, 1.0 Gy MLD reduction was at the expense of 3.3 Gy MHD. Recalculations of the plans on repeated CTs showed a decrease in target coverage for plans with a lower MHD (Figure 2). Conclusion: Large differences in photon treatment plans were observed between Dutch centres regarding MHD (up to 13.3 Gy) and MLD (up to 3.3 Gy) in EC. Lowering MHD seems to have limited impact on MLD, but compromises plan robustness in case of anatomical changes. These results will serve as a foundation for building consensus on optimising treatment strategies in EC.