Estimation of effective dose at thyroid cancer patients treated with I¹³¹

Full text of publication follows. Radioiodine therapy for thyroid cancer patients and hyperthyroid patients at the Institute of Pathophysiology and nuclear medicine is performed in a form of capsules. During the oral application it is reasonable to presume that 15 minutes in stomach is long enough to make additional exposure to stomach as well to other organs nearby. It is almost impossible to perform direct measurements to estimate internal doses of organs, so it is rather recommended to estimate the dose by calculation. Absorbed energy per unit transformation in stomach and surrounding organs has been calculated. The dose equivalents in several internal organs have been calculated in aim to determine the effective doses using appropriate tissue weighting factor values. The MCNP-4b model was used for this calculation. The phantom model was created using three major sections: - an elliptical cylinder representing the trunk and arms - two truncated circular cones representing the legs and feet - a circular cylinder on which sits an elliptical cylinder capped by half an ellipsoid representing the neck and head. The stomach wall is represented by the volume between two concentric ellipsoids and the contents by the volume within the inner ellipsoid. Also TLD measurements were performed over gastric region for limited time of 15 minutes. Estimated effective dose was highest in stomach 7,43*10^-02 Sv. The estimated values for other organs like colon, liver, lungs, ovary and bone surface was less than the estimated effective dose of stomach. (authors)