Prognostic Value of Head and Neck Tumor Proliferative Sphericity From 3’-Deoxy-3’-[18F] Fluorothymidine Positron Emission Tomography

[
¹⁸
F] fluorothymidine (
¹⁸
F-FLT) positron emission tomography (PET) can be used for quantifying tumor proliferation and its changes during chemoradiotherapy (CRT) in head and neck squamous cell carcinoma (HNSCC). We investigated the complementary prognostic value of sphericity (one of several available 3-D shape descriptors) and standard metrics in
¹⁸
F-FLT PET images before and during CRT regarding 4-year disease-free survival (DFS). Forty-eight HNSCC patients treated with CRT underwent
¹⁸
F-FLT PET/CT before and during CRT. Median follow-up was 52 months. Primary tumors were automatically delineated and characterized by extracting max and mean standardized uptake value (SUV), proliferative volume and associated sphericity. Prognostic value for DFS of clinical and imaging features was assessed using Kaplan-Meier survival analysis. In univariate analysis after correction for multiple testing, the per-treatment sphericity (HR = 4.2, p = 0.02) and SUVmean (HR = 4.1, p = 0.03) were prognostic factors, whereas none of the pretreatment variables were significant. Reduction in SUVmax (HR = 4, p = 0.04) was also a prognostic factor, but not reduction of proliferative tumor volume. The best stratification of patients for DFS was achieved by combining per-treatment SUVmean and sphericity (HR = 6.7, p <; 0.001). High sphericity combined with low mean
¹⁸
F-FLT uptake during treatment were associated with better DFS. These results suggest the potential prognostic value of tumor characterization from
¹⁸
F-FLT PET in HNSCC that may be further explored in larger cohorts.