Abstract
68Ga-NODAGA-exendin-4 is a promising tracer for β-cell imaging using PET/CT. Possible applications include preoperative visualization of insulinomas and discrimination between focal and diffuse forms of congenital hyperinsulinism. There is also a significant role for this tracer in extending our knowledge on the role of β-cell mass in the pathophysiology of type 1 and type 2 diabetes by enabling noninvasive quantification of tracer uptake as a measure for β-cell mass. Calculating radiation doses from this tracer is important to assess its safety for use in patients (including young children) with benign diseases and healthy individuals. Methods: Six patients with hyperinsulinemic hypoglycemia were included. After intravenous injection of 100 MBq of the tracer, 4 successive PET/CT scans were obtained at 30, 60, 120, and 240 min after injection. Tracer activity in the pancreas, kidneys, duodenum, and remainder of the body were determined, and time-integrated activity coefficients for the measured organs were calculated. OLINDA/EXM software, version 1.1, was applied to calculate radiation doses using the reference adult male and female models and to estimate radiation doses to children. Results: The mean total effective dose for adults was very low (0.71 ± 0.07 mSv for a standard injected dose of 100 MBq). The organ with the highest absorbed dose was the kidney (47.3 ± 10.2 mGy/100 MBq). The estimated effective dose was 2.32 ± 0.32 mSv for an injected dose of 20 MBq in newborns. This dose decreased to 0.77 ± 0.11 mSv/20 MBq for 1-y-old children and 0.59 ± 0.05 mSv for an injected dose of 30 MBq in 5-y-old children. Conclusion: Our human PET/CT-based dosimetric calculations show that the effective radiation doses from the novel tracer 68Ga-NODAGA-exendin-4 are very low for adults and children. The doses are lower than reported for other polypeptide tracers such as somatostatin analogs (2.1–2.6 mSv/100 MBq) and are beneficial for application as a research tool, especially when repeated examinations are needed.
Highlights
IntroductionThe radiopharmaceutical 68Ga-NODAGA-exendin-4 binds to the glucagonlike peptide 1 receptor, which is expressed on pancreatic b-cells [1]
68Ga-NODAGA-exendin-4 is a promising tracer for β-cell imaging using PET/CT
Clinical studies have shown the potential of 111In-labeled exendin for detection of such tumors with SPECT/ CT [5,6,7]. 68Ga-exendin PET/CT has been demonstrated to be superior to 111In-exendin SPECT/CT in a small crossover clinical trial [8], and its superiority over conventional imaging was shown in a large prospective trial [9]
Summary
The radiopharmaceutical 68Ga-NODAGA-exendin-4 binds to the glucagonlike peptide 1 receptor, which is expressed on pancreatic b-cells [1] It is a promising tracer for in vivo targeting of b-cells using PET/CT, with several possible applications in clinical diagnostics for insulin-producing lesions and in diabetes research. In addition to these clinical applications, 68Ga-NODAGA-exendin-4 has great potential as a research tool to determine b-cell mass in vivo. This technique can contribute to knowledge about the role of b-cell mass in the pathophysiology of diabetes For these applications of 68Ga-NODAGA-exendin-4, a low effective radiation dose is important, especially if repeated imaging is a possibility. We performed human PET-based dosimetry on adults with suspected insulinoma to determine effective radiation doses and organ-absorbed doses, and we extrapolated these data to estimate radiation doses to children
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