S2141
Physics - Inter-fraction motion management and daily adaptive radiotherapy
ESTRO 2026
and reduces cardiac dose compared to the non- adaptive approach. Heart-based adaptation meaningfully lowers MHD and predicted mortality without compromising target coverage, while target- based adaptation improves coverage without significantly increasing cardiac exposure. These results support systematic, dose-based adaptation triggers to balance tumor control and adverse events in esophageal proton therapy. Keywords: protons, adaptation, accumulation, esophagus
Accumulation (SPA): used only the initial plan for all fractions.Target coverage (ITV/GTV D98%) and organ of interest metrics (mean heart/lung dose – MHD/MLD, heart V40Gy) were evaluated. The 2-year mortality probability was calculated according to the Dutch indication protocol. All values are reported as means; differences between SPA and MPA were assessed using two-tailed paired t-tests. Results: For adapted patients, MPA improved target coverage compared with SPA (ITV D98% 95.8 → 97.1, p=0.028; GTV D98% 98.9 → 99.7, p<0.001). Gains were most pronounced in patients adapted for target underdosage (ITV 95.0 → 96.9; GTV 98.9 → 99.7). Coverage improvement (any D98% increase between SPA and MPA) occurred in 81% of adapted patients for ITV and 88% for GTV, while non-adapted patients had higher baseline coverage due to more favorable anatomy. When comparing SPA to MPA, MHD decreased from 12.0 Gy to 11.6 Gy (p=0.002), heart V40 from 7.9% to 7.0% (p<0.001), while MLD remained unchanged. In the heart-overdose subgroup, MHD reduction reached ~1 Gy without compromising target coverage. Predicted 2-year mortality decreased by 0.6 pp overall and by 1.5 points in heart-adapted patients (33.9% → 32.4%, p=0.001).
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What dose do we deliver? Dosimetric comparison of planned dose vs accumulated dose in a large cohort of lung patients RIchard Canters, Jarno Huijs, Bas Nijsten, Michel Oellers, Esther Kneepkens, Dirk De Ruysscher Department of Radiation Oncology (Maastro), GROW School for Oncology and Reproduction, Maastricht University Medical Centre+, Maastricht, Netherlands
Purpose/Objective: Lung anatomy is prone to changes during the
radiotherapy treatment course. Dose recalculation on the daily CBCTs and deformable dose accumulation (DDA) can provide information about the quality of irradiation beyond the anatomy . In this study, we evaluated given fraction doses and accumulated doses for a large cohort of lung patients. Material/Methods: A retrospective cohort of 147 patients was evaluated. 46 Patients received stereotactic treatment, while 101 patients received long course treatment. All patients were treated without any plan adaptation. Dose recalculations on CBCTs were performed using a monte carlo algorithm (XVMC), after which DDA on the planning CT was performed in Raystation 2024B using the intensity based Anaconda algorithm (Raysearch, Stockholm, Sweden). We evaluated the V95% in the primary (CTVp) and nodal (CTVn) CTVs, as well as mean heart dose (MHD) and mean lung dose (MLD). Results: In the individual fraction recalculations, CTVp V95%>95% in 86.7% of fractions, while in 71.2% of patients all fractions receive adequate dose. In accumulated dose, 94.4% of patients received adequate dose to the CTVp. In the CTVn, V95%>95% in 83.1% of fractions, while 51% of patients experienced no underdosage during treatment course. In accumulated dose, this increased to 87.8% (Figure 1). MHD increases of >1Gy occurred in 4.0% of fractions, while in accumulated dose this was reduced to 2.0%. For MLD these numbers were 3.0% and 0.7% respectively (Figure 2).
Conclusion: Adaptive proton therapy improves target robustness
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