Repeatability of tumour hypoxia imaging using [¹⁸F]EF5 PET/CT in head and neck cancer

Hypoxia contributes to radiotherapy resistance and more aggressive behaviour of several types of cancer. This study was designed to evaluate the repeatability of intratumour uptake of the hypoxia tracer [¹⁸F]EF5 in paired PET/CT scans. Ten patients with newly diagnosed head and neck cancer (HNC) received three static PET/CT scans before chemoradiotherapy: two with [¹⁸F]EF5 a median of 7 days apart and one with [¹⁸F]FDG. Metabolically active primary tumour volumes were defined in [¹⁸F]FDG images and transferred to co-registered [¹⁸F]EF5 images for repeatability analysis. A tumour-to-muscle uptake ratio (TMR) of 1.5 at 3 h from injection of [¹⁸F]EF5 was used as a threshold representing hypoxic tissue. In 10 paired [¹⁸F]EF5 PET/CT image sets, SUVmean, SUVmax, and TMR showed a good correlation with the intraclass correlation coefficients of 0.81, 0.85, and 0.87, respectively. The relative coefficients of repeatability for these parameters were 15%, 17%, and 10%, respectively. Fractional hypoxic volumes of the tumours in the repeated scans had a high correlation using the Spearman rank correlation test (r = 0.94). In a voxel-by-voxel TMR analysis between the repeated scans, the mean of Pearson correlation coefficients of individual patients was 0.65. The mean (± SD) difference of TMR in the pooled data set was 0.03 ± 0.20. Pretreatment [¹⁸F]EF5 PET/CT within one week shows high repeatability and is feasible for the guiding of hypoxia-targeted treatment interventions in HNC. (orig.)