Dosimetric evaluations using images of scanning predose of patients undergoing radioiodine therapy

Abstract

Radioiodine Therapy is a technique for thyroid cancer treatment. In this technique, thyroidectomized patients are submitted to the incorporation of a radioactive substance iodide of sodium (Na131I) that reacts physiologically with the metastasis, thyroid tissue remains and other organs and tissues of the human body. The locations of these reactions are known as areas of larger concentration, hyper collector areas or hyper concentrator areas, (“hot-areas" or sourceorgans) and are visualized through nuclear medicine images known as pre-dose (anterior and posterior). To obtain those images, patient receives, through his mouth, a small dose of 131I with low activity (± 74 MBq), later he is positioned in the gleam camera. According to the presences of hot-area shown in the image, the nuclear doctor determines the activity to be administrated in the treatment. This analysis is purely qualitative.  In this study, the images of scanning predose were adjusted to the dimensions of the Voxel phantom – FAX, and the hot-area ones corresponds to the internal sources of the proposed model. For the calculations of the coefficients of conversions between equivalent dose and accumulated activity in the principal organs radio sensible,  the FAX and the source were coupled to the code of transport of the radiation EGS4 (Electron Gamma Shower, version 4). The obtained results with this computational model were compared with others similar published. It is possible to esteem the equivalent doses in patient’s radio sensible organs and tissues using the conversion coefficients here developed.