18F-Fluorothymidine radiation dosimetry in human PET imaging studies.
3'-Deoxy-3'-(18)F-fluorothymidine ((18)F-FLT) is a PET imaging agent that shows promise for studying cellular proliferation in human cancers. FLT is a nucleoside analog that enters cells and is phosphorylated by human thymidine kinase 1, but the 3' substitution prevents further incorporation into DNA. We estimated the radiation dosimetry for this tracer from data gathered in patient studies.


METHODS
Time-dependent tissue concentrations of radioactivity were determined from blood samples and PET images of 18 patients after intravenous injection of (18)F-FLT. Radiation-absorbed doses were calculated using the MIRD Committee methods, taking into account variations that were based on the distribution of activities observed in the individual patients. Effective dose equivalent (EDE) was calculated using International Commission on Radiological Protection Publication 60 tissue weighting factors for the standard man and woman.


RESULTS
For a single bladder voiding at 6 h after (18)F-FLT injection, the (18)F-FLT EDE (mean +/- SD) was 0.028 +/- 0.012 mSv/MBq (103 +/- 43 mrem/mCi) for a standard male patient and 0.033 +/- 0.012 mSv/MBq (121 +/- 43 mrem/mCi) for a standard female patient. The organ that received the highest dose was the bladder (male, 0.179 mGy/MBq [662 mrad/mCi]; female, 0.174 mGy/MBq [646 mrad/mCi]), followed by the liver (male, 0.045 mGy/MBq [167 mrad/mCi]; female, 0.064 mGy/MBq [238 mrad/mCi]), the kidneys (male, 0.035 mGy/MBq [131 mrad/mCi]; female, 0.042 mGy/MBq [155 mrad/mCi]), and the bone marrow (male, 0.024 mGy/MBq [89 mrad/mCi]; female, 0.033 mGy/MBq [122 mrad/mCi]).


CONCLUSIONS
Organ dose estimates for (18)F-FLT are comparable to those associated with other commonly performed nuclear medicine tests, and the potential radiation risks associated with (18)F-FLT PET imaging are within accepted limits.
Vesselle
Hubert
H
Department of Radiology, Division of Nuclear Medicine, University of Washington Medical Center, Seattle, Washington 98195, USA. vesselle@u.washington.edu
Grierson
John
J
Peterson
Lanell M
LM
Muzi
Mark
M
Mankoff
David A
DA
Krohn
Kenneth A
KA
D000368:Aged; D000369:Aged, 80 and over; D015224:Dideoxynucleosides / Q000493:pharmacokinetics*; D005260:Female; D006801:Humans; D008175:Lung Neoplasms / Q000000981:diagnostic imaging* / Q000378:metabolism*; D008297:Male; D008657:Metabolic Clearance Rate; D008875:Middle Aged; D009928:Organ Specificity; D011829:Radiation Dosage; D011865:Radioisotope Dilution Technique; D011874:Radiometry / Q000379:methods* / Q000592:standards; D019275:Radiopharmaceuticals / Q000493:pharmacokinetics; D018570:Risk Assessment / Q000379:methods*; D014018:Tissue Distribution; D014055:Tomography, Emission-Computed / Q000379:methods*; D014915:Whole-Body Counting / Q000379:methods*
D015224:Dideoxynucleosides; D019275:Radiopharmaceuticals; C002854:alovudine