ESTRO 2025 - Abstract Book

S993

Clinical – Head & neck

ESTRO 2025

1726

Mini-Oral Clinical Feasibility and Dosimetric Benefits of Online Adaptive Radiotherapy for Nasopharyngeal Carcinoma Yu-Xian Yang 1 , Guang-Yu Wang 1 , Xiao-Bo Jiang 1 , Li Lin 1 , Xin Yang 1 , Kang Zhang 2 , Bing-Huan Li 2 , Hua Li 3 , Le-Cheng Jia 3 , Yan-Fei Liu 3 , Dan-Ning Fu 2 , Wei Zhang 2 , Jing-Jie Zhou 2 , Chi Feng 1 , Xiao-Yan Huang 1 , Yan-Ping Mao 1 , Rui Guo 1 , Guan Qun Zhou 1 , Ying Sun 1 1 Radiation oncology, Sun Yat-sen University Cancer Center, State Key Laboratory of Oncology in South China, Collaborative Innovation Center for Cancer Medicine, Guangdong Key Laboratory of Nasopharyngeal Carcinoma Diagnosis and Therapy, Guangzhou, China. 2 Technical support, Shanghai United Imaging Healthcare Co., Ltd., Shanghai, China. 3 Technical support, Shenzhen United Imaging Research Institute of Innovative Medical Equipment, Shenzhen, China Purpose/Objective: To evaluate the clinical feasibility and dosimetric benefits of online adaptive radiotherapy (ART) for patients with nasopharyngeal carcinoma (NPC). Material/Methods: We prospectively enrolled treatment-naïve, non-metastatic patients with NPC undergoing radical radiotherapy, with all participants receiving online ART. Online ART efficiency and patient motion were evaluated. The original contours were transferred to the new computed tomography (CT) as rigidly registered contours and compared with AI generated contours based on the new CT. The original plans were transposed to the new CT with modified contours as scheduled plans and compared with the ART plans. Results: From April 2022 to November 2023, 122 patients were enrolled, with 120 completing the online ART workflow. Median workflow time, not including patient setup, was 20.79 minutes (Figure 1). Mean vector motion was 0.46 mm from CT scan to plan approval and 0.32 mm during treatment delivery. AI-generated contours showed significantly higher dice similarity coefficients compared to rigidly registered contours (0.98 vs. 0.52 for involved cervical lymph nodes, 0.98 vs. 0.97 for high-risk clinical target volumes, and 0.92 vs. 0.88 for low-risk clinical target volumes) (all P < 0.001). Compared to scheduled plans, ART plans improved coverage for all targets, with the mean planning target volumes receiving 100% of the prescription dose increasing by 0.3% to 13.2% (all P < 0.05). Furthermore, ART plans reduced dose to all organs at risk (OARs), with the greatest benefits observed in the parotids, optic nerves, and optic chiasm, which experienced dose reductions of 993.5 ± 1125.4 cGy, 397.3 ± 576.5 cGy, and 349.6 ± 562.4 cGy, respectively (all P < 0.001) (Table 1) .