RT Journal Article SR Electronic T1 PET-Based Radiation Dosimetry in Man of 18F-Fluorodihydrotestosterone, a New Radiotracer for Imaging Prostate Cancer JF Journal of Nuclear Medicine JO J Nucl Med FD Society of Nuclear Medicine SP 1966 OP 1971 VO 45 IS 11 A1 Pat B. Zanzonico A1 Ronald Finn A1 Keith S. Pentlow A1 Yusuf Erdi A1 Bradley Beattie A1 Timothy Akhurst A1 Olivia Squire A1 Michael Morris A1 Howard Scher A1 Timothy McCarthy A1 Michael Welch A1 Steven M. Larson A1 John L. Humm YR 2004 UL http://jnm.snmjournals.org/content/45/11/1966.abstract AB 16β-fluoro-5α-dihydrotestosterone (FDHT) is a promising new PET radiopharmaceutical for the imaging of prostate cancer. A recent clinical trial provided the opportunity for refinement of normal-tissue radiation-absorbed dose estimates based on quantitative PET. The objective of the current study was to derive estimates of normal-tissue absorbed doses for 18F-FDHT administered to patients with advanced prostate cancer. Methods: Absorbed dose estimates were derived from 10 18F-FDHT PET studies (administered activity, 111–407 MBq) of 7 prostate cancer patients. Activity concentrations in plasma and red marrow (assuming a plasmacrit of 0.58, an extracellular fluid fraction of 0.40, and equilibration of activity between plasma and marrow extracellular fluid) were measured ex vivo from a peripheral blood sample. Liver, spleen, urinary bladder contents, and total-body activities were measured by region-of-interest analysis of quantitative whole-body studies acquired with a dedicated PET scanner. Total organ activities and residence times were calculated from the respective PET scan-derived activity concentrations assuming standard (70 kg) man organ masses. Urinary excretion was corrected for hepatobiliary excretion (liver activity), and a first-order adjustment was made for the bladder-wall mass based on the patient’s total-body mass. Mean organ absorbed doses were calculated with the MIRD formalism and the standard man model using the MIRDOSE3 software program. Results: The absorbed doses (mean ± SD) ranged from 0.00057 ± 0.000281 cGy/MBq (to skin) to 0.00868 ± 0.00481 cGy/MBq (to bladder wall) (voiding intervals, 1–2 h), and the effective dose equivalent was 0.00177 ± 0.000152 cSv/MBq. Conclusion: The maximum absorbed dose among all tissues in all 10 studies, 0.0151 cGy/MBq, occurred for the urinary bladder wall (with hydration and 1- to 2-h voiding intervals). To ensure that the maximum normal-tissue absorbed dose is kept below the recommended maximum permissible dose of 5 cGy per single administration, a maximum administered activity of 331 MBq (5 cGy/[0.0151 cGy/MBq]) is recommended for 18F-FDHT.