Blood dosimetry from a single measurement of the whole body radioiodine retention in patients with differentiated thyroid carcinoma

    1. Christoph Reiners
    1. Department of Nuclear Medicine, University of Würzburg, Oberdürrbacher Straße 6, D-97080 Würzburg, Germany
      1Divisions of Endocrinology and Nuclear Medicine, Departments of Internal Medicine and Radiology, The Ohio State University, 446 McCampbell Hall, 1581 Dodd Drive Columbus, OH 43210-1296, USA
    1. (Correspondence should be addressed to H Hänscheid; Email: haenscheid{at}


    A simple method is presented to estimate the radiation-absorbed dose to the blood after radioiodine administration from a single external measurement of the whole-body retention in patients suffering from differentiated thyroid cancer. The blood dose is calculated applying the formalism of the Medical International Radiation Dose Committee under the assumptions that whole-body activity decays exponentially and that 14% of the whole-body residence time can be attributed to the blood. Accuracy and applicability of the method were tested based on data from 29 assessments, 18 pre-therapeutic tracer studies, and 11 ablation therapies, with whole-body and blood-retention measurements over at least 4 days. The mean of the absolute deviations between estimates and actual blood doses was found to be 14%, if external whole-body counting was performed on day 1 or 2 after radioiodine administration. This simple formalism is: 1) applicable to pre-therapeutic dosimetry for remnant ablation or treatment of metastases in a blood dose-based treatment concept and 2) applicable to blood-dose estimates after radioiodine therapy to determine radiation exposure. When combined with a measurement of the whole body retention 1 or 2 days after radioiodine administration this single time-point method closely approximates the classic, yet much more labor intensive multi-day dosimetry that measures both blood and whole-body activities.

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