ESTRO 2025 - Abstract Book

S3139

Physics - Inter-fraction motion management and offline adaptive radiotherapy

ESTRO 2025

Conclusion: A strict online matching and supervision strategy has been successfully implemented into the HYPO-RT-PC-boost trial. The frequency of patient re-positioning indicates a reasonable online supervision tolerance. The size of the shift between CBCT bone match and kV-kV fiducial marker match motivates future investigations into a reduction of the pelvic lymph node margins.

Keywords: Dose painting, High-risk prostate, Clinical trial

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Digital Poster Development of robust dose accumulation for proton therapy of patients with lung and esophageal cancer Richard Canters 1 , Djoya Hattu 1 , Maaike Berbee 1 , Dirk De Ruysscher 1 , Vicki Trier Taasti 1,2 1 Department of Radiation Oncology (MAASTRO), GROW-School for Oncology, Maastricht University Medical Center, Maastricht, Netherlands. 2 Danish Particle Therapy Centre, Arhus University Hospital, Arhus, Denmark Purpose/Objective: Patients undergoing proton therapy for lung or esophageal cancer often show anatomical changes during treatment. Reliable dose accumulation is essential to assess the given dose during the treatment. Therefore, in this study we developed a dose accumulation method incorporating residual uncertainties. Material/Methods: We included 20 lung and 20 esophageal cancer patients, treated at our proton center. Treatment plans were robustly optimized with 5 mm setup and 3% range uncertainty. Each patient received weekly repeat CTs (reCTs), on which we recalculated the treatment plan in 28 scenarios representing residual uncertainties (1 mm setup, 3% range uncertainty). All scenario doses were deformed from the individual reCTsto the planning CT (pCT) using two types of deformable image registration (DIR) inRayStation (RaySearch Laboratories, Stockholm, Sweden): only intensity-based DIR versus use of controlling ROIs (lungs, heart, and ITV/CTV) to guide the DIR. The doses were accumulated on the pCT in a weighted manner, assigning a number of fractions/plans to each reCT. Then voxel-wise minimum/maximum (VWmin/VWmax) doses were generated (Figure 1). The target coverage on the summed dose was evaluated for the ITV expanded with 3 mm (esophagus) or 2 mm (lung), as well as the nodal CTV (lung). Results: For esophagus patients, 67% (50/75) of reCTs showed an adequate ITV_3mm coverage of V94%>98%. For lung patients, coverage was adequate (V95%>95%) in 73% (68/93) of reCTs for primary tumors, and in 93% (63/68) of reCTs for nodes. The summed dose showed a better coverage with 75% of esophagus patients having adequate coverage for both DIR methods. The lung patients had adequate coverage of the primary tumor for 95% (controlling ROIs) vs 90% (no controlling ROIs) of patients, while for nodes 100% (controlling ROIs) vs 93% (no controlling ROIs) of patients experienced adequate coverage (Figure 2). Conclusion: The robust dose accumulation provided a method to assess the total delivered dose, while incorporating residual uncertainties. For most of the lung patients, target coverage appeared to be adequate in the accumulated dose, despite a larger rate of under-dosage in individual reCTs. A similar behavior was observed for the esophagus patients, although the number of patients experiencing under-dosage was relatively high. Evaluation on ITV_3mm may be too conservative, though. Differences between dose accumulation without or with controlling ROIs only showed small dose differences. However, in some patients, the use of controlling ROIs clearly improved target coverage, suggesting that a contour guided DIR is beneficial in dose accumulation.