Tc-99m methyl diphosphonate (MDP) bone scintigraphy is used to assess disease activity in rheumatoid arthritis (RA). Somatostatin receptor (SSTR) expression in RA has been reported previously. SSTR-based PET/computed tomography (CT) may be superior to bone scintigraphy to know disease extent and in locating inflammatory joints that can be further targeted with peptide receptor radionuclide therapy thereby opening up new theranostic avenues. Based on these facts, the present study was designed to compare Tc-99m MDP bone scintigraphy and Ga-68 DOTANOC PET/CT in patients with RA.
Materials and methods
Patients with a clinical diagnosis of RA were injected with 111–185 MBq of Ga-68 DOTANOC and 740 MBq of Tc-99m MDP intravenously. Images were acquired 30–45 min postinjection for Ga-68 DOTANOC on dedicated PET/CT scanners. Triple-phase bone scans were acquired on a dual-head gamma camera. PET/CT and MDP scan images were visually assessed by two experienced nuclear medicine physicians.
Nineteen patients (16 women and 3 men) with a clinical diagnosis of RA were included in the study. Clinically, 196 joints in these 19 patients were diagnosed positive for RA. Of these 196 joints, Tc-99m MDP uptake was seen in 157 joints (80%). On Ga-68 DOTANOC scan, tracer uptake was seen in 151 of 196 joints (77%) with a lesion to background ratio of at least 2 in most of the joints.
Ga-68 DOTANOC is equally good as an MDP scan for detection of RA with the added advantage of being used as a theranostic modality. However, further evaluation with a larger sample size and joint-to-joint comparison is warranted.