2883 - Cone Beam Computed Tomography (CBCT)-Based Imaging Tracking of Primary Tumor, Lymph Nodes, and Parotid Glands in Nasopharyngeal Carcinoma (NPC) for Tailored Treatment Strategy and Functional Preservation
Presenter(s)
Z. Dong1, B. Li1, G. Q. Zhou1, Z. Q. Lin1, S. He2, D. Y. Dai1, J. Y. Wang3, C. Y. He1, K. B. Yang1, J. Du1, Y. Zhang1, X. Liu1, Y. Xiang2, Y. Huang1, Y. P. Mao1, F. Han1, L. Tang4, Y. Sun5, J. Ma1, and C. Xu1; 1Department of Radiation Oncology, Sun Yat-sen University Cancer Center, State Key Laboratory of Oncology in South China, Guangdong Provincial Clinical Research Center for Cancer, Guangdong Key Laboratory of Nasopharyngeal Carcinoma Diagnosis and Therapy, Guangzhou, China, 2Department of Nasopharyngeal Carcinoma, State Key Laboratory of Oncology in South China, Collaborative Innovation Center for Cancer Medicine, Guangdong Key Laboratory of Nasopharyngeal Carcinoma Diagnosis and Therapy, Sun Yat-sen University Cancer Center, Guangzhou, China, 3Department of Basic Research, Sun Yat-sen University Cancer Center, State Key Laboratory of Oncology in South China, Guangdong Provincial Clinical Research Center for Cancer, Guangdong Key Laboratory of Nasopharyngeal Carcinoma Diagnosis and Therapy, Guangzhou, China, 4Department of Radiation Oncology, Sun Yat-sen University Cancer Center, State Key Laboratory of Oncology in South China, Guangdong Provincial Clinical Research Center for Cancer, Guangdong Key Laboratory of Nasopharyngeal Carcinoma Diagnosis and Therapy, Guangzhou, Guangdong, China, 5State Key Laboratory of Oncology in South China, Guangdong Key Laboratory of Nasopharyngeal Carcinoma Diagnosis and Therapy, Guangdong Provincial Clinical Research Center for Cancer, Department of Radiation Oncology, Sun Yat-sen University Cancer Center, Guangzhou, Guangdong, China
Purpose/Objective(s): Imaging and tracking the changes in NPC lesions and parotid glands during radiotherapy (RT) helps clarify the role of PD-1 blockade alongside concurrent chemoradiotherapy (CCRT), identify the optimal timing for adaptive RT replanning, and preserve parotid gland function.
Materials/Methods: Eligible pts (N = 404) with stage III–IVa NPC were consecutively enrolled from 2020 to 2023 and received weekly CBCT before each of the 33 RT fractions (fx), with 88 pts selected for daily CBCT validation. Using specific bony landmarks for indirect delineation, 5 representative levels depicting primary tumor were outlined on each CBCT cross-sectional scan from sphenoid sinus to pterygoid process. Changes in primary tumor were estimated by calculating the differences in mean area for each fx compared to baseline. Lymph nodes and parotid glands were directly outlined at their maximum planes. One-way repeated measures ANOVA identified change-plateau inflection points. Generalized estimating equations compared differences between groups, adjusting for baseline area, weight loss during RT, and antibiotic use. Parotid gland function was assessed using the EORTC H&N35 questionnaire. Kaplan-Meier analysis and Cox regression were used for event-free survival (EFS) and overall survival (OS).
Results: K-means clustering analysis based on 26,642 and 4,041 CBCT images individually showed that primary tumor and lymph nodes can be categorized into 2 distinct patterns of rapid regression and slow regression, which were validated by the daily CBCT group. Analysis of 5,572 CBCT images showed that parotid glands shrank continuously during RT and were exclusively related to primary tumor changes (p = 0.018). The rapid regression group had clinically and statistically deteriorated dry mouth (p = 0.033) and sticky saliva (p = 0.049) post-RT compared to slow regression group, with a later inflection point at the 21st fx (vs 11th fx). While PD-1 blockade + CCRT compared with CCRT did not affect parotid gland changes, it led to slower regression of the primary tumor (n = 86 vs 271 [well-matched baseline and prior treatment]; p = 0.035) and lymph nodes (n = 47 vs 47 [after 1:1 propensity score matching]; p = 0.005). Analysis of individual patient data indicated that patients whose primary tumor showed early regression by the 6th fx had significantly higher 3-year EFS (hazard ratio [HR] = 0.37; p = 0.031) and OS (HR = 0.24; p = 0.043) compared to those without early regression.
Conclusion: NPC lesions exhibited rapid and slow regression patterns during RT, with the 6th fx serving as a crucial assessment node. Triple regimen with CCRT may not be a suitable timing to combine PD-1 blockade. It is proposed that the rapid/slow regression group consider RT replanning at the 21st/11th fx to optimize primary tumor regression while protecting parotid glands.