engleski

Radioiodine uptake in thyroid cancer patients after diagnostic application of low i-131 dose

The aim of our study was to investigate the influence of diagnostic administration of 74 MBq of I-131 on subsequent uptake of therapeutic radioiodine in thyroid cancer patients. The retention measurements were performed by whole body counter in 24 patients 6 weeks after total thyreoidectomy. Profile scans were performed 2, 24, 48 and 72 hours after administration of the diagnostic activity and 72 hours after administration of the ablation-therapeutic activity (4.4 GBq). The mean effective half-life of the diagnostic activity in thyroid remnants was 40.3 ± ; ; 23.0 hours (range 15.5 - 88.8). The radioiodine uptake in thyroid remnants obtained with the subsequent ablation activity 72 hours after administration was in average only 30.4% ± ; ; 19.8% (range 6.8% - 73.4%) of those predicted by the diagnostic study. The more pronounced uptake reduction was connected with longer effective half-life of iodine and higher 24-hours uptake in thyroid remnants, with longer time interval between surgery and administration of the diagnostic activity and shorter period between administration of the diagnostic and ablation activity. Our results showed that diagnostic activity of 74 MBq of I-131 markedly reduced thyroid uptake during ablation procedure, what should be taken into account in a radiation dose planning, whenever a quantitative dosimetric study is used.

thyroid cancer ; radioiodine therapy ; in vivo dosimetry

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