The biokinetics and dosimetry of (111)In-DOTA-NOC-ATE (NOCATE), a high-affinity ligand of SSTR-2 and SSTR-5, and (111)In-DTPA-octreotide (Octreoscan?, OCTREO) were compared in the same patients.
Seventeen patients (10 men, 7 women; mean age 60 years), referred for an OCTREO scan for imaging of a neuroendocrine tumour (15), thymoma (1) or medullary thyroid carcinoma (1), agreed to undergo a second study with NOCATE. Whole-body anterior-posterior scans were recorded 0.5 (100 % reference scan), 4, 24 and 48 h (17 patients) and 120 h (5 patients) after injection. In 16 patients the OCTREO scan (178 ± 15 MBq) was performed 16 ± 5 days before the NOCATE scan (108 ± 14 MBq) with identical timing; 1 patient had the NOCATE scan before the OCTREO scan. Blood samples were obtained from 14 patients 5 min to 48 h after injection. Activities expressed as percent of the initial (reference) activity in the whole body, lung, kidney, liver, spleen and blood were fitted to biexponential or single exponential functions. Dosimetry was performed using OLINDA/EXM.
Initial whole-body, lung and kidney activities were similar, but retention of NOCATE was higher than that of OCTREO. Liver and spleen uptakes of NOCATE were higher from the start (p < 0.001) and remained so over time. Whole-body activity showed similar ? and ? half-lives, but the ? fraction of NOCATE was double that of OCTREO. Blood T (1/2)? for NOCATE was longer (19 vs. 6 h). As a result, the effective dose of NOCATE (105 ?Sv/MBq) exceeded that of OCTREO (52 ?Sv/MBq), and the latter result was similar to the ICRP 106 value of 54 ?Sv/MBq. Differential activity measurement in blood cells and plasma showed an average of <5 % of NOCATE and OCTREO attached to globular blood components.
NOCATE showed a slower clearance from normal tissues and its effective dose was roughly double that of OCTREO.