[62Cu]DOTA-NOC

We aimed to elucidate the role of quantitative tumor burden based on PET/CT of somatostatin receptors in well-differentiated neuroendocrine tumors (NETs).

This study enrolled patients with [⁶⁸ Ga]Ga-DOTA-NOC PET/CT-positive advanced NETs who did not receive medical treatment prior to PET/CT. Tumor burden was calculated using methods based on the background threshold and relative fixed threshold values (30%, 40%, and 50%). The prognostic value of the measured tumor burden in reference to overall survival (OS) and progression-free survival (PFS) on treatment with octreotide long-acting repeatable (LAR) was assessed using Cox regression analysis, Harrell's C-index, and survival analysis. A classification and regression tree (CART) was used to determine the optimal threshold for tumor burden.

A total of 204 patients were included. Somatostatin receptor-expressing tumor volume (SRETV) and liver SRETV derived from a relative fixed threshold of 30% (SRETV₃₀ and liver SRETV₃₀) were statistically significantly associated with OS (C-index: 0.802 [95% confidence interval (CI), 0.658-0.946] and 0.806 [95% CI, 0.664-0.948], respectively). Extrahepatic tumor burden was not correlated with OS (hazard ratio: 0.617, 95% CI: 0.241-1.574, P = 0.312). Among 155 patients with non-functional NETs with a ki-67 index of ≤ 10%, those with a high SRETV₃₀ (P = 0.016) or high liver SRETV₃₀ (P = 0.014) showed statistically significantly worse PFS on treatment with octreotide LAR. Patients receiving a higher dose of octreotide LAR normalized by SRETV₃₀ or liver SRETV₃₀ (a normalized dose or a liver normalized dose) showed prolonged PFS on treatment with octreotide LAR and a prolonged OS.

Quantitative tumor burden based on [⁶⁸ Ga]Ga-DOTA-NOC PET/CT was correlated with OS and PFS in patients with non-functional NETs with a ki-67 index of ≤ 10% who received octreotide LAR. Calculating normalized and liver normalized doses may help in selecting the starting dose of octreotide LAR.

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.

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.