S2142
Physics - Inter-fraction motion management and daily adaptive radiotherapy
ESTRO 2026
Conclusion: Overall accumulated dose on the primary CTV was adequate, while we saw slightly more underdosage in the nodal CTV. Possible relevant changes in OARs were only occurring in a few patients, who may benefit from adaptation to reduce dose. Keeping in mind that this patient group received no adaptation, moving from an anatomy-based to a dose-based adaptation protocol is likely to benefit nodal CTV coverage, while the clinical benefit should be subject for investigation.
patients frequently experience anatomical variations, leading to discrepancies between the delivered and planned doses. Adaptive radiotherapy can compensate for these deviations; however, its optimal timing remains unclear. This study explores the use of an improved cumulative sum (CUSUM) chart for personalized monitoring of these variations to guide ART decisions. Material/Methods: We retrospectively analyzed data from 24 NPC patients treated with the Radixact X7 Tomotherapy System (Accuray, Sunnyvale, USA). Daily megavoltage computed tomography (MVCT) scans acquired prior to irradiation were reviewed using the PreciseART tool. Initial structures were propagated to each MVCT image using image registration. The planned dose was mapped to each daily MVCT image based on rigid registration performed at the time of treatment. Spearman's rank correlation coefficient was employed to analyze the correlation between volume change ( Δ V) and dose change ( Δ D). In the improved CUSUM chart, the parameter value from the first treatment MVCT scan was employed as the target value (T). The upper and lower control limits (UCL and LCL) are defined as 7%*T for the target volume and 15%*T for the OARs. The improved CUSUM charts were used to track parameter variations in target volumes and organs at risk (OARs) throughout treatment. Results: The correlation coefficients between Δ V and Δ D for target volumes and OARs ranged from -0.59 to 0.49. The improved CUSUM charts were used to monitor dose metric variations in target volumes and OARs at each fraction for each patient. Only the gross tumor volume of lymph nodes (GTVnd) and the left and right parotid glands showed a relatively consistent trend of increasing dose. However, other structures showed no consistent trends in dosimetric variation. Variations were observed to be organ- and patient-dependent. Furthermore, different target and OAR dose metrics exceeded their control limits at varying treatment fractions. The majority of these breaches first occurred between fractions 5 and 10.
Keywords: dose accumulation, dose evaluation, lung
Digital Poster 2853 An improved cumulative sum chart guides adaptive radiotherapy decisions in nasopharyngeal carcinoma patients
Sijia Chen 1 , Xiang Gao 1 , Yimin Li 1 , Chuanben Chen 2 1 Department of Radiation Oncology, The First Affiliated Hospital of Xiamen University, Xiamen, China. 2 Department of Radiation Oncology, Fujian Medical University Cancer Hospital & Fujian Cancer Hospital, Fuzhou, China
Purpose/Objective: During radiotherapy for nasopharyngeal carcinoma,
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