Modelos, simuladores, dosimetria e respostas imunológicas radioinduzidas em cintilografia de perfusão do miocárdio

Abstract

The cardiovascular diseases CVD acquired greater importance during the twentieth century, due to increased life expectancy of the general population. Each year, a large number of individuals have a diagnosis of CVD. Those can be evaluated by the radiological and scintigraphic images, with the helping of the radiology and nuclear medicine. The main useful tracers for Myocardial Perfusion Imaging - MPI are thalium- 201; fluor-18 fluordeoxyglucose FDG; and, the tracer target with technecium-99 metastable; mainly the 99mTc-sestamibi and the 99mTc-tetrosfomin. The dose evaluation of the scintigraphic procedure can auxiliary the radiation exposition reduction. On this context, investigations were performed in heart dosimetry, applied to the usual radiopharmaceuticals for MPI, based on computational tools, physical phantom simulators, and radiobiological studies. Following, investigations in radiobiology and in possible deterministic effects were addressed. At the present thesis, a physical heart phantom was developed made of tissue-elastomeric with mass density and chemical composition equivalent to the human tissues. A three-dimensional model of the heart, in stereolithographic format - STL, with anatomic details and high precision was developed for future fast prototyping. The radiopharmaceutical dosimetry for thalium- 201 was simulated with the support of the SISCODES and MCNP codes, elucidating the spatial dose absorption at the cardiac muscle, per unit of radioisotope activity, and the dose versus volume histogram. Adding to these studies, radiobiological investigations were addressed, analyzing the deterministic effects in peripheral blood mononuclear cells PBMC, and the analysis of the jugulodigastric lymph nodes, in an animal model. The findings was that the radiation induces phenotypic differences in cellular lines; reducing the subpopulation of T CD5 CD4 cells, with increasing of the CTLA-4 expression. And, it was demonstrated from the histopathology analysis that the constitutive cells of the lymph nodes after radiation exposition, the B and T lymphocytes and the conjunctive tissues presented an inflammatory process resulting cellular death and loss of the lymph nodes functions. The present results support the relevance of this investigation in the MPI dosimetry and in the deterministic effects stimulated by radiation in specific organs. These findings will help in the choosing the most appropriated radiopharmaceutical to MPI considering the fundamental and universal aspects of the radioprotection.