Substantial reductions in the thyroid volume (up to 70-80%) after radioiodine therapy for Graves' hyperthyroidism are common and have been reported in the literature. However the effect of thyroid volume reduction on the calculation of the committed radiation dose has not been evaluated. In this paper a mathematical model of thyroid mass reduction during the clearance phase after I-131 administration to patients affected by Gr aves' disease, is presented, demonstrating that the mass reduction of the gland in the first month after the therapy has a considerable effect oil the calculated committed radiation dose. It is assumed that thyroid volume reduction soon after therapy administration is linearly correlated with the specific activity in the gland. This can be expressed by a differential equation that can be easily solved assuming a monoexponential clearance function for the iodine in thyroid. The solution m(t) gives the change in thyroid mass during the first month after therapy, and depends on the maximum activity in thyroid, on the effective half-time, on the mass of the gland before the therapy and on the individual's rate of change in thyroid mass over time. A set of measurements of thyroid volume was made by ultrasonography (7.5 MHz probe) on twenty-nine patients affected by Graves' disease. The measurements were made before and after I-131 treatment, during the iodine clearance phase. The experimental data were fitted with the equation m(t) and demonstrated good agreement with the proposed model. Doses calculated considering the change in mass were as much as 25% different than those calculated using traditional methods (i.e not considering a variable thyroid mass). The mathematical model of thyroid mass reduction is in good agreement with our experimental data. it is very simple and can be used to provide the reduction of thyroid mass during the First month after the therapy using parameters that can be easily evaluated. The model should be used in the algorithms for the calculation of the radiation committed dose to the thyroid. A worksheet for the calculation of the committed dose and for the evaluation of the reduction of the mass of the thyroid is also presented. This worksheet is: very simple to use. it can help physicians in the evaluation of mass changes and cumulative absorbed dose in I-131 therapy of the GI aves' disease.
A mathematical model of thyroid mass reduction after radioiodine therapy of Graves’ disease
FERDEGHINI, Marco;
2001-01-01
Abstract
Substantial reductions in the thyroid volume (up to 70-80%) after radioiodine therapy for Graves' hyperthyroidism are common and have been reported in the literature. However the effect of thyroid volume reduction on the calculation of the committed radiation dose has not been evaluated. In this paper a mathematical model of thyroid mass reduction during the clearance phase after I-131 administration to patients affected by Gr aves' disease, is presented, demonstrating that the mass reduction of the gland in the first month after the therapy has a considerable effect oil the calculated committed radiation dose. It is assumed that thyroid volume reduction soon after therapy administration is linearly correlated with the specific activity in the gland. This can be expressed by a differential equation that can be easily solved assuming a monoexponential clearance function for the iodine in thyroid. The solution m(t) gives the change in thyroid mass during the first month after therapy, and depends on the maximum activity in thyroid, on the effective half-time, on the mass of the gland before the therapy and on the individual's rate of change in thyroid mass over time. A set of measurements of thyroid volume was made by ultrasonography (7.5 MHz probe) on twenty-nine patients affected by Graves' disease. The measurements were made before and after I-131 treatment, during the iodine clearance phase. The experimental data were fitted with the equation m(t) and demonstrated good agreement with the proposed model. Doses calculated considering the change in mass were as much as 25% different than those calculated using traditional methods (i.e not considering a variable thyroid mass). The mathematical model of thyroid mass reduction is in good agreement with our experimental data. it is very simple and can be used to provide the reduction of thyroid mass during the First month after the therapy using parameters that can be easily evaluated. The model should be used in the algorithms for the calculation of the radiation committed dose to the thyroid. A worksheet for the calculation of the committed dose and for the evaluation of the reduction of the mass of the thyroid is also presented. This worksheet is: very simple to use. it can help physicians in the evaluation of mass changes and cumulative absorbed dose in I-131 therapy of the GI aves' disease.
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