18F]-FDG-PET/CT and [18F]-FAZA-PET/CT Hypoxia Imaging of Metastatic Thyroid Cancer: Association with Short-Term Progression After Radioiodine Therapy.

Abstract

To examine the relationships between 2-deoxy-2-[18F]fluoro-D-glucose ([18F]-FDG) and hypoxia tracer [18F]fluoro-azomycinarabinofuranoside ([18F]-FAZA) and between 131I and [18F]-FAZA uptake in patients with metastatic thyroid cancer and to evaluate imaging features associated with short-term progression after 131I therapy. The study population was 20 patients (17 women and 3 men; mean age, 67years) with metastatic thyroid cancer who underwent both [18F]-FDG- and [18F]-FAZA-positron emission tomography (PET)/X-ray computed tomography (CT) examinations before 131I therapy. Short-term response to radioiodine was assessed (mean follow-up, 19months ± 9). PET parameters including [18F]-FDG-SUVmax, [18F]-FAZA-SUVmax, and [18F]-FAZA-tumor-to-muscle [T/M] were obtained. Mann-Whitney U, Wilcoxon signed-rank, or χ2 tests were used to assess differences between two quantitative variables or compare categorical data. Predictive factors for short-term progression were investigated with logistic regression analysis. Eleven lymph node metastatic lesions were identified in 9 patients and 46 distant metastatic lesions (lung, 19; bone, 17; and liver, 10) in 14 patients. A total of 24 131I-positive and 33 131I-negative lesions were detected. SUVmax was significantly lower with [18F]-FAZA-PET/CT (1.3 ± 0.6) than with [18F]-FDG-PET/CT (6.4 ± 5.9, p < 0.001). No significant correlation was observed between [18F]-FAZA-PET/CT and 131I imaging concerning visibility (p = 0.36). After 131I therapy, 31 of 57 metastatic lesions displayed short-term progression. Multivariate logistic regression revealed that [18F]-FDG-SUVmax (p = 0.022) and [18F]-FAZA-T/M (p = 0.002) showed significant associations with short-term progression. Although [18F]-FAZA uptake was low in metastatic thyroid cancers, not only glucose metabolism but also hypoxic conditions may be associated with progression after 131I therapy in patients with metastatic thyroid cancer.