Does ¹⁸F-sodium fluoride PET/CT have a role in the assessment of response to ²²³Ra therapy in men with prostatic bone metastases?

Abstract

BackgroundThe REASURE study investigated imaging biomarkers in men receiving ²²³Ra treatment for prostate cancer bone metastases. We used REASURE data to compare and contrast the roles of [¹⁸F]NaF PET/CT measurements of maximum standardised uptake value (SUVmax) and bone metabolic flux (Ki) as markers of response.MethodsThirty-four men with prostatic bone metastases received up to six cycles of ²²³Ra (55 or 88 kBq/kg) at four-weekly intervals. Whole-body diffusion-weighted MRI and [¹⁸F]NaF PET/CT images were acquired at baseline and 4, 12, and 24 weeks later. Values of the apparent diffusion coefficient (ADC, a measure of tumour response), SUVmax, and a novel surrogate measurement of Ki using a PET/CT SUV measurement in the left ventricle were monitored in up to 5 bone metastases in each participant. Multilinear regression analysis (MLR) was performed to determine if changes in ADC were predicted by changes in SUVmax or Ki. Radium dose and baseline SUVmax were additional independent variables.ResultsADC values increased throughout the study, while SUVmax and Ki decreased. MLR analysis showed that baseline SUVmax and ²²³Ra dose predicted ADC response (P ConclusionsBaseline SUVmax was the best predictor of ADC response, followed by ²²³Ra dose. Changes in SUVmax and Ki failed to predict changes in ADC, suggesting that the changes in the PET/CT variables reflected the effect of ²²³Ra uptake on osteoblasts rather than a tumoricidal effect. A decrease in SUVmax seen on post-therapy [¹⁸F]NaF PET/CT scans should not be interpreted as evidence of tumour regression.Trial registrationISRCTN ISRCTN17805587. Registered 21/01/15.