Suppression of myocardial glucose metabolism in FDG PET/CT: impact of dose variation in heparin bolus pre-administration.

INTRODUCTION: Adequate suppression of physiologic myocardial glucose uptake is important to ensure the interpretability and diagnostic reliability of [18F]fluorodeoxyglucose (FDG) PET/CT studies performed in the context of cardiac inflammation and infection. This study describes our experience with 4 preparatory protocols used in our institution. METHODS: FDG PET/CT scans were performed according to 4 preparatory protocols (716 scans total), i.e. 6-h fast (group 1), low-carbohydrate diet plus 12-h fast (group 2), low-carbohydrate diet plus 12-h fast plus intravenous heparin pre-administration (15 IU/kg) (group 3), and low-carbohydrate diet plus 12-h fast plus intravenous heparin pre-administration (50 IU/kg) (group 4). Consecutive scans were retrospectively included from time frames during which the particular protocol was used. FDG uptake in normal myocardium was scored on a scale ranging from 0 (uptake less than that in the left ventricular blood pool) to 4 (diffuse uptake greater than that in the liver). Complete suppression was defined as uptake less than or equal to the blood pool (scores 0-1). RESULTS: Complete suppression was accomplished in 27% in group 1, 68% in group 2, 69% in group 3 and 81% in group 4. Complete suppression was significantly lower in group 1 compared with all other groups (P < 0.0001 for all comparisons) and significantly higher in group 4 compared with group 2 (P = 0.005) and group 3 (P = 0.007). Groups 2 and 3 did not differ significantly (P = 0.92). CONCLUSION: A total of 50 IU/kg single-dose heparin administration before FDG PET/CT in addition to a low-carbohydrate diet and prolonged fast significantly outperformed protocols with no or lower dose (15 IU/kg) heparin in completely suppressing myocardial glucose metabolism.

Comparison of [(177)Lu-DOTA(0),Tyr(3)]octreotate and [(177)Lu-DOTA(0),Tyr(3)]octreotide: which peptide is preferable for PRRT?

PURPOSE: Patients with somatostatin receptor subtype 2-positive metastasised neuroendocrine tumours can be treated with [(177)Lu-DOTA(0),Tyr(3)]octreotate. Some use octreotide as the peptide for peptide receptor radionuclide therapy (PRRT). We compared in seven patients [(177)Lu-DOTA(0),Tyr(3)]octreotide ((177)Lu-DOTATOC) and [(177)Lu-DOTA(0),Tyr(3)]octreotate ((177)Lu-DOTATATE), to see which peptide should be preferred for PRRT with (177)Lu. METHODS: In the same patients, 3,700 MBq (177)Lu-DOTATOC and 3,700 MBq (177)Lu-DOTATATE was administered in separate therapy sessions. Amino acids were co-administered. Whole-body scanning was performed on days 1, 4 and 7 post therapy. Blood and urine samples were collected. We calculated residence times for tumours, spleen and kidneys. RESULTS: All patients had longer residence times in spleen, kidneys and tumours after use of (177)Lu-DOTATATE (p=0.016 in each case). Comparing (177)Lu-DOTATATE with (177)Lu-DOTATOC, the mean residence time ratio was 2.1 for tumour, 1.5 for spleen and 1.4 for kidneys. Dose-limiting factors for PRRT are bone marrow and/or kidney dose. Although the residence time for kidneys was longer when using (177)Lu-DOTATATE, the mean administered dose to tumours would still be advantageous by a factor of 1.5, assuming a fixed maximum kidney dose is reached. Plasma radioactivity after (177)Lu-DOTATATE was comparable to that after (177)Lu-DOTATOC. Urinary excretion of radioactivity was comparable during the first 6 h; thereafter there was a significant advantage for (177)Lu-DOTATOC. CONCLUSION: (177)Lu-DOTATATE had a longer tumour residence time than (177)Lu-DOTATOC. Despite a longer residence time in kidneys after (177)Lu-DOTATATE, tumour dose will always be higher. Therefore, we conclude that the better peptide for PRRT is octreotate.