S2145
Physics - Inter-fraction motion management and daily adaptive radiotherapy
ESTRO 2026
rated grade ≥ 2 dysphagia NTCP 6 months post- treatment were compared between Adaptclassic and Adaptshrink, and between VMAT and IMPT.
Results: On average, the GTV shrank to 63% of the original size for the primary tumor, while the lymph nodes shrank to 80% throughout treatment. Most patients benefited from the Adaptshrink protocol, reducing mean doses to OOIs compared to Adaptclassic (Figure 2). IMPT plans consistently achieved lower doses than VMAT, and while adaptation reduced OOI doses for both, the magnitude of these reductions were comparable, indicating that GTV-based adaptation did not enhance the inherent advantage of IMPT. The magnitude of dose reduction did not depend solely on GTV reduction (Figure 2), but also on the spatial relationship between the GTV and OOIs. Although average NTCP reductions for dysphagia were modest ( ≤ 0.5%), individual patients showed improvements reaching 2.7%.
Conclusion: This in-silico planning study shows that MRI-guided target adaptation provided modest dose reduction in >75% of patients compared to a classic adaptive approach. As weekly adaptation is resource-intensive and not always beneficial, further studies are needed to identify ideal candidates based on pre-treatment characteristics. Keywords: HPV-positive OPC, IMPT, organ-of-interest sparing Daily Adaptive Radiotherapy in Head and Neck Squamous Cell Carcinoma May Introduce Dose- Protocol Failures Hedda Enocson 1,2 , André Haraldsson 1,2 , Per Engström 2 , Sofie Ceberg 1 , Maria Gebre-Medhin 3,4 , Gabriel Adrian 3,4 , Per Munck af Rosenschöld 1,2 1 Medical Radiation Physics, Lund University, Lund, Sweden. 2 Radiation Physics, Department of Hematology, Oncology, and Radiation Physics, Skåne University Hospital, Lund, Sweden. 3 Oncology, Department of Clinical Sciences Lund, Lund University, Lund, Sweden. 4 Oncology, Department of Hematology, Oncology, and Radiation Physics, Skåne University Hospital, Lund, Sweden Digital Poster Highlight 2876
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