2706 - Correlation of Metabolic Response Assessed by PET-CT Metrics with Survival in Locally Advanced Nasopharyngeal Carcinoma

Purpose/Objective(s): Locally advanced nasopharyngeal carcinoma (LA-NPC) is the most common presentation of NPC. There is a great need for prognostic factors in LA-NPC due to the limited value of the TNM staging system. This study aimed to evaluate the prognostic value of 18F-FDG PET-CT metrics following chemotherapy and after definitive chemoradiation in locally advanced NPC.

Materials/Methods: Using a cohort of 107 LA-NPC patients recruited for a clinical trial with a different aim, patients underwent a pretreatment PET-CT scan, a scan two weeks after completing two cycles of induction chemotherapy, and a scan 12 weeks after concurrent definitive chemoradiotherapy. The PET-CT scans were analyzed using the maximum Standardized Uptake Value (SUVmax), Metabolic Tumor Volume (MTV), and Total Lesion Glycolysis (TLG). Correlations were assessed using Cox proportional hazards regression for continuous and ordinal variables, and Kaplan-Meier survival analysis with log-rank testing was used to evaluate significance.

Results: There was no significant correlation between PET-CT metrics of the primary tumor after chemotherapy, whether measured by SUVmax, MTV, or TLG. However, there was a significant correlation between PET-CT metrics of the involved lymph nodes after chemotherapy, specifically TLG with relapse-free survival (RFS, p=0.003), metastasis-free survival (MFS, p=0.007), and overall survival (OS, p=0.010). Similarly, PET-CT metrics measured by SUVmax in the involved lymph nodes after definitive chemoradiotherapy correlated significantly with RFS (p<0.001) and MFS (p=0.01), but not OS. A Clinician-Assessed PET Response (CA PET) was also evaluated. The response was considered “complete” if SUVmax was < 4, “partial” if SUVmax was > 4, and “progressed tumor” if SUVmax surpassed its value at diagnosis or if there were new lesions. CA PET strongly correlated with DFS (p<0.001), MFS (p<0.001), and OS (p<0.001).

Conclusion: Our findings support the use of PET-CT metrics after chemotherapy as a valuable early prognostic marker for risk stratification in locally advanced NPC, potentially guiding therapeutic decisions and improving personalized treatment strategies. Our clinician-assessed PET response, which evaluates PET-CT scans before and after therapy completion, outperformed interval-specific PET measurements. Further research is warranted to optimize the use of PET-CT metrics in diagnosis and therapeutic monitoring of LA-NPC.