Total volume and total activity of 18F-NaF-avid fibrous dysplasia of bone lesions is positively associated with established bone turnover markers (BTMs).

1161 Aim: Fibrous dysplasia (FD) of bone is a benign skeletal disorder characterized by the replacement of normal bone and normal bone marrow with abnormal fibro-osseous tissue leading to significant morbidity. In a cohort of 15 FD patients we have previously reported positive association between FD-related18F-NaF activity in the entire skeleton, with established markers of bone activity, includingserum levels of alkaline phosphatase (Alk Phos) and osteocalcin (OC), and urine levels of N-terminaltelopeptide (NTX). Aim of the current study was to confirm these findings in a much larger cohort of 44 FD patients. Patients and Methods: Forty four FD patients (26 females, 18 males) underwent whole-body 18F-NaF-PET/CT scans at the NIH Clinical Center. Mean age±std at the time of the scan was: 30.1±14.9 years. PET scans were obtained (mean ± SD) 61.8±5.1minutes after intravenous administration of anaverage±std of 2.69±0.73mCi of 18F-NaF. Low dose, non-contrast, CT scans were acquired for coregistration and attenuation correction purposes. FD-related 18F-NaF activity was assessed by using MIM vista (version 6.5.9). Firstly, a VOI encompassing the entire skeleton was drawn, and afterwards a SUVmax threshold-based approach -customized per patient- was employed in order to include all FD-related bone uptake. Separate VOIs encircling all areas above the SUVmax threshold, were automatically generated, while areas with physiologic or non-FD related 18F-NaF activity (e.g. activity in the urinary tract, inflammatory uptake) were manually removed. Subsequently, the following skeletal disease indices were automatically ontained: Total Volume (TV) of all 18F-NaF positive skeletal FD lesions and FD-related 18F-NaF activity (TA) in the entire skeleton determined as the product of TV multiplied by SUVmean of all FD lesions (TA = TV×SUVmean). Results: Pearson’s correlation test revealed that TV and TA obtained from 18F-NaF-avid FD-lesions in the entire skeleton were positively associated with serum levels of alkaline phosphatase, osteocalcin and urine levels of NTX:(TV: r=0.744, p<0.001 Alk Phos; r=0.429, p=0.013 OC ; r=0.746, p<0.001 NTX) (TA:r=0.460, p=0.009 Alk Phos; r=0.382, p=0.022 OC ; r=0.475, p=0.007 NTX)(P-values were adjusted for false discovery rate) Conclusions: We confirm in a larger cohort of FD patients that FD-associated 18F-NaF activity strongly correlates with established bone turnover markers, further enhancing the finding that 18F-NaF-PET/CT accurately reflects underlying bone processes encountered in FD, and implying the employment of the modality for the in vivo assessment of FD activity.