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A Journal on Nuclear Medicine and Molecular Imaging
Affiliated to the and to the International Research Group of Immunoscintigraphy
Indexed/Abstracted in: Current Contents/Clinical Medicine, EMBASE, PubMed/MEDLINE, Science Citation Index (SciSearch), Scopus
Impact Factor 2,413
DOSIMETRY IN NUCLEAR MEDICINE - PART I
Jentzen W., Freudenberg L., Bockisch A.
Department of Nuclear Medicine, University of Duisburg-Essen, Essen, Germany
Iodine-131-labelled agents are successfully used in cancer treatment. In the pretherapy dosimetry approach, positron emission tomography/computed tomography (PET/CT) using 124I provides a modality to estimate absorbed dose to tumours and can be considered as the preferred imaging method for this purpose in 131I radiopharmaceutical therapies. For accurate dosimetry, serial measurements of activity concentrations (ACs) over an appropriate time period are necessary. Consequently, accurate AC determination is of paramount importance in PET/CT-based lesion dosimetry using 124I-labelled agents. After presenting an historical overview of 124I clinical application, this review focuses on factors impairing PET image quantification accuracy and on methods of correcting for these effects. Specifically, the emission of prompt gamma photons in the 124I decay process that are detected in coincidence with each other and with the annihilation photon, and the low 124I positron branching ration of only 23% raise concerns regarding image quantification accuracy. This review discusses this prompt gamma effect, its impact and approaches to correct for this phenomenon. In 124I lesion dosimetry, recovery coefficients (RCs) are commonly used to compensate primarily for partial-volume effect but also, in a simplistic way, for prompt gamma coincidence effect; the main methodological factors affecting the RC-corrected 124I AC are described. Finally, special issues in image 124I quantification are reviewed, including coadministration of high therapeutic activities of 131I, shine-through artefact, and transmission-contamination effect occurring in stand-alone PET systems.