ESTRO 2025 - Abstract Book

S3337

Physics - Intra-fraction motion management and real-time adaptive radiotherapy

ESTRO 2025

3885

Digital Poster Patient specific 4D photon dose reconstruction and accumulation based on treatment log files : a framework for adaptive radiotherapy assessment Zahra Ahmadi ganjeh 1 , Daniele Cannavo 1 , sabine Visser 1 , Erik Korevaar 2 , Gerolf Meulman 3 , Stefan Both 3 , Gabriel Gutterres Marmitt 1 1 Department of Radiation Oncology, University Medical Center Groningen, groningen, Netherlands. 2 Department of Radiation Oncology, Korevaar, Groningen, Netherlands. 3 Department of Radiation Oncology, University Medical Center Groningen, Groningen, Netherlands Purpose/Objective: Anatomical changes and motion-induced uncertainties can compromise radiotherapy accuracy for moving tumors 1,2 . This proof-of-concept study presents an automated framework to longitudinally evaluate patient specific impact of setup, anatomical changes and motion on treatment quality in clinical volumetric modulated arc therapy (VMAT) via four-dimensional (4D) photon dose reconstruction and accumulation. Material/Methods: We developed a python script for 4D photon dose reconstruction and accumulation in the RaySearch treatment planning system for patients with moving tumors. This method utilizes patient specific treatment delivery log files, breathing records, and multiple repeat 4DCTs collected during the course of treatment for 19 lung cancer patients with large target motion (>10 mm). Control points, cumulative monitor units (MU), gantry angles, and multi-leaf collimator (MLC) positions were the key parameters to create 10 RT subplans based on the log file. For each fraction, delivered doses were estimated on 4DCT phases using log file data and a selected segments of the breathing ANZAI output corresponding to beam delivery. Dose distributions from different respiration phases were warped with deformable image registration (DIR) and accumulated on the reference CT, and finally wraped with DIR on the reference pCT resulting in a dose distribution for 8 fractions (Fig.1). Dosimetric results, including target homogeneity (D2 - D98) and dose to 98% of the CTV (D98) , were reported.

Figure 1 . Overview of the 4D Dose Reconstruction and Accumulation workflow.illustrating the steps involved in mapping, processing, and accumulating dose distributions from multiple 4DCT phases.

Results: Fig. 2 presents the D98 relative to the prescribed dose and the D2 - D98 values per fraction for the cohort. The deviation between the estimated delivered log dose and the planned dose showed discrepancies in D98 ranging from 0.02% for patient (P)15 to 6.02% for P14. The discrepancies in the D2 - D98 with differences range from 1.0 to 6.5 Gy highlighting the substantial impact of treatment machine delivery accuracy, anatomical variations and breathing respiratory motion on treatment accuracy.