@article {Zanzonico1966, author = {Pat B. Zanzonico and Ronald Finn and Keith S. Pentlow and Yusuf Erdi and Bradley Beattie and Timothy Akhurst and Olivia Squire and Michael Morris and Howard Scher and Timothy McCarthy and Michael Welch and Steven M. Larson and John L. Humm}, title = {PET-Based Radiation Dosimetry in Man of 18F-Fluorodihydrotestosterone, a New Radiotracer for Imaging Prostate Cancer }, volume = {45}, number = {11}, pages = {1966--1971}, year = {2004}, publisher = {Society of Nuclear Medicine}, abstract = {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{\textendash}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{\textquoteright}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 {\textpm} SD) ranged from 0.00057 {\textpm} 0.000281 cGy/MBq (to skin) to 0.00868 {\textpm} 0.00481 cGy/MBq (to bladder wall) (voiding intervals, 1{\textendash}2 h), and the effective dose equivalent was 0.00177 {\textpm} 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.}, issn = {0161-5505}, URL = {https://jnm.snmjournals.org/content/45/11/1966}, eprint = {https://jnm.snmjournals.org/content/45/11/1966.full.pdf}, journal = {Journal of Nuclear Medicine} }