Optimised tracer-dependent dosage cards to obtain weight-independent effective doses
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The aim of this study was twofold: firstly, to determine whether the European Association of Nuclear Medicine (EANM) dosage card results in weight-independent effective doses or weight-independent count rates; secondly, to determine whether one dosage card is sufficient for 95 different radiopharmaceuticals, and, if not, how many cards we reasonably need to take into account inter-tracer variability.
Normalisation factors for count rate and effective dose were calculated as a function of body weight, with 70 kg as standard. Calculations were performed, using whole-body absorption fractions and MIRDOSE 3 software, for seven anthropomorphic phantoms and ten radionuclides. An analytic function for both relations was proposed. Normalisation factors for effective dose for 95 radiopharmaceuticals were investigated using cluster analysis.
Normalisation factors for count rate and effective dose can be estimated accurately as a function of body weight W by (W/70) a holding only one parameter, called the a value. The a values for 95 radiopharmaceuticals were classified into three clusters (nA = 7, nB = 76, nC = 12). Cluster A contains tracers for renal studies. Cluster B contains all remaining tracers, except iodine-labelled tracers for thyroid studies and 89Sr for therapy, which belong to cluster C.
Correction factors proposed by the EANM task group mainly correct for effective dose. They are very similar to the factors obtained for cluster A. Using the EANM factors for tracers belonging to clusters B and C results in significantly higher effective doses to children. We suggest using three tracer-dependent dosage cards for which the correction factors have been calculated to obtain weight-independent effective doses.
KeywordsEffective dose MIRDOSE Dosage card Count rate Radiation risk
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