Human biodistribution and radiation dosimetry of the tachykinin NK 1 antagonist radioligand [18F]SPA-RQ: Comparison of thin-slice, bisected, and 2-dimensional planar image analysis

David R. Sprague, Frederick T. Chin, Jeih San Liow, Masahiro Fujita, H. Donald Burns, Richard Hargreaves, James B. Stubbs, Victor W. Pike, Robert B. Innis, P. David Mozley

Research output: Contribution to journalArticle

22 Scopus citations

Abstract

18F-Labeled substance P antagonist-receptor quantifier ([ 18F]SPA-RQ) [2-fluoromethoxy-5-(5-trifluoromethyl-tetrazol-1-yl)- benzyl]-[(2S,3S)-2-phenyl-piperidin-3-yl)amine] is a selective radioligand for in vivo quantification of tachykinin NK1 receptors with PET. The aims of this study were to estimate the radiation safety profile and relative risks of [18F]SPA-RQ with 3 different methods of image analysis. Methods: Whole-body PET images were acquired in 7 healthy subjects after injection of 192 ± 7 MBq (5.2 ± 0.2 mCi) [18F]SPA-RQ. Emission images were serially acquired at multiple time-points from 0 to 120 min and approximately 180-240 min after injection. Urine samples were collected after each imaging session and for 24 h after the last scan to measure excreted radioactivity. Horizontal tomographic images were compressed to varying degrees in the anteroposterior direction to create 3 datasets: thin-slice, bisected, and 2-dimensional (2D) planar images. Regions of interest were drawn around visually identifiable source organs to generate time-activity curves for each dataset. Residence times were determined from these curves, and doses to individual organs and the body as a whole were calculated using OLINDA/EXM 1.0. Results: The lungs, upper large intestine wall, small intestine, urinary bladder wall, kidneys, and thyroid had the highest radiation-absorbed doses. Biexponential fitting of mean bladder and urine activity showed that about 41% of injected activity was excreted via urine. Assuming a 2.4-h urine voiding interval, the calculated effective doses from thin-slice, bisected, and 2D planar images were 29.5, 29.3, and 32.3 μSv/MBq (109, 108, and 120 mrem/mCi), respectively. Conclusion: Insofar as effective dose is an accurate measure of radiation risk, all 3 methods of analysis provided quite similar estimates of risk to human subjects. The radiation dose was moderate and would potentially allow subjects to receive multiple PET scans in a single year. Individual organ exposures varied among the 3 methods, especially for structures asymmetrically located in an anterior or posterior position. Bisected and 2D planar images almost always provided higher organ dose estimates than thin-slice images. Thus, either the bisected or 2D planar method of analysis appears acceptable for quantifying human radiation burden, at least for radioligands with a relatively broad distribution in the body and not concentrated in a small number of radiation sensitive organs.

Original languageEnglish (US)
Pages (from-to)100-107
Number of pages8
JournalJournal of Nuclear Medicine
Volume48
Issue number1
StatePublished - Jan 1 2007

Keywords

  • Biodistribution
  • PET dosimetry
  • [18F]SPA-RQ

ASJC Scopus subject areas

  • Radiology Nuclear Medicine and imaging

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