ESTRO 2025 - Abstract Book

S3965

Radiobiology - Tumour radiobiology

ESTRO 2025

462

Digital Poster Clinical Evidence and Characteristics of Tumor Spatial Dose-Response Assessed in the Induction Chemotherapy of nasopharyngeal carcinoma patients Shu Zhang 1,2 , Xiao Qiang Chen 3 , Jiao Na Dai 4 , Rong Tian 4 , Nian Yong Chen 1,2 , Di Yan 3 1 Department of Head and Neck Oncology, West China Hospital, Sichuan University, Chengdu, China. 2 Department of Radiation Oncology, West China Hospital, Sichuan University, Chengdu, China. 3 Radiotherapy Physics and Technology Center, West China Hospital, Sichuan University, Chengdu, China. 4 Department of Nuclear Medicine, West China Hospital, Sichuan University, Chengdu, China Purpose/Objective: To investigate clinical evidence and characteristics of tumor spatial dose-response matrix (DRM) assessed using feedback 18 F-FDG-PET/MRI image in the induction chemotherapy (IC) for nasopharyngeal carcinoma (NPC). Material/Methods: PET/MRI images were obtained both pre- and post-IC for the advanced NPC patients who underwent three-cycle IC and concurrent chemoradiotherapy (CCRT). Tumor voxel DRM IC was generated using the two-point images mentioned above. DRM IC >0.8 and SUVavid >3 voxels were used to define the rSubvolume and aSubvolume, respectively. The relationship between DRM IC , rSubvolume, aSubvolume clinical characteristics, and clinical treatment response was analyzed. The possibility of DPbN for the highly resistant tumor voxel (DRM IC >0.8) was explored. The corresponding adaptive radiotherapy plans were generated for dosimetric analysis.

Results: The mean and coefficient variation (CV) of primary tumor DRM (DRM nx

IC ) were significantly higher than those of the

positive lymph nodes (DRM nd IC ). The mean DRM IC was lower in the EBV-DNA clearance group compared to the EBV DNA persistent group (p=0.006). However, no differences in DRM IC were observed across T, N, age, gender, or smoking status subgroups. The proportion of aSubvolume inside rSubvolume ranged from 0.78% to 82.98%. The rSubvolume distribution was more scattered in PR patients than in CR patients. Adaptive radiotherapy with three hypo-fractionated boosts to the rSubvolume was achievable without increasing the doses to surrounding OARs, except for the temporal lobe.