Determınation of the dosage due to neigboring organs according to the activity of I-131 radioisotopes used in hypertroid treatment by monte carlo method

There are many ways to be exposed to radiation in life, whether it is ionizing or not. Although non-ionizing radiation is not harmful; medical applications, especially for therapeutic or diagnostic purposes, are the most important cause of severe exposure for ionizing radiation. For exposed to ionizing radiation in medical applications, diagnostic Computed Tomography scans are in the first place, while nuclear medicine used for both diagnosis and treatment is in the second place. Consequently, as the dose absorbed by the tissues exposed to ionizing radiation and therefore the organs increases, the risks to health also increase in direct proportion. In nuclear medicine, due to the radioisotopes placed in the body for diagnostic and/or therapeutic purposes, not only the organs and tissues where the tumor is located, but also other neighborhood organs and tissues absorb the dose, albeit in various amounts. In this thesis, the Monte Carlo-based NCINM code were used for evaluation of changings in the doses. For this purpose, the iodine radioisotope (I-131) was placed to thyroid gland in male phantoms aged newborn, 1, 5, 10 and 15 years in simulation. The activities of the I-131 are selected as to use it in treatment of thyroid disease and thyroid cancer. The neighborhood organs were determined as thyroid, thymus and lymph nodes which are the most effective in growth of babies.