Dosimetry methodology for diagnostic nuclear medicine

Abstract

For diagnostic dosimetry in nuclear medicine, quantitative imaging and activity measurements of blood and urine samples are essential. This is followed by the calculation of the absorbed organ doses and the effective dose. To achieve this, a correct temporal sampling and the use of adequate procedures to integrate the time-activity curves to obtain the total number of decays in the source organs (the time-integrated activity coefficients, TIACs) are prerequisites. If the TIACs are known, a calculation of the absorbed doses is performed by applying the “MIRD formalism”: D = TIAC · A 0 · S D: the mean absorbed dose to a target from a source region. A 0 : administered activity S: mean absorbed dose per unit cumulated activity in the target region. The S-values used for diagnostics are still based on mathematical phantoms. Although, the ICRP in its publication 103 requires the use of a set of gender-specific realistic voxel phantoms, the S-values for isotopes, however, are not yet made publicly available. For diagnostics the effective dose is the main protection quantity. It is calculated using the tissue weighting factors established by the ICRP in the publications ICRP60 and ICRP103. The effective dose, however, is only intended to calculate the risk for an age-independent reference person, not the individual risk. It is a protection quantity and is related to the probability of health detriment to an adult reference person due to stochastic effects from exposure to low doses of ionizing radiation.