Introduction: Thyroid cancer is at the ninth from ten of common malignant cancer. A man has higher risk to get Thyroid cancer that a woman has. This organ is lain near human neck. The use of radioactive I-131, I-123 and Tc-99m for diagnosis of thyroid cancer has a risk where other organs around Thyroid will accept dose of radiation. One of the risks is large dose which is accepted by brain, skin and lung. Large dose accepted those organs will make a high defect at those organs. To reduce that problem, we have to know the problem dose which is accepted by cell cancer and the organs. One of is to make a simulation of interaction of radiation particle with organ. The simulation used to determine the intermine the interaction of radiation particles and matter is a Monte Carlo method. One of Monte Carlo software is MCNPX (Monte Carlo N-Particle) made by a team from Los Alamos National Laboratory. It can simulate particles interaction with real situation. The use of Monte Carlo in radiation transport is an effective way to predict absorbed dose in an organ. According to Krstic, MCNP can be used to simulate dose in organs by Prostate Brachytherapy showed that MCNP calculation can determine dose in organ. The use of a well-supported radiation transport code such as MCNP with knowledge of patient anatomy will result in a significant improvement in the accuracy of dose calculations. This study simulates Thyroid cancer with Male and Female ORNL- MIRD phantom and uses I-131, I-123 and Tc-99m radioactive which are distributed with MCNPX program.
Materials and Methods: Materials used in this research were ORNL-MIRD database geometry. The exterior of phantom has approximately the form of the human body. . The simulation used to determine the interaction of radiation particles and matter is a Monte Carlo method. One of Monte Carlo software is MCNPX made by a team from Los Alamos National Laboratory. It can simulate particles interaction with real situation.
Results: MCNP simulation simulates radiation process to obtain dose in organ. The absorbed dose in Thyroid and other organs increased every rising activity of I-123,I-131 and Tc-99m used, but the absorbed dose in other organs was less than in Thyroid.
Conclusion: The calculation results was obtained that absorbed dose in Thyroid would increase by rise of I-123, I-131 and Tc-99m activity but absorbed dose in other organs around Thyroid such as Brain, Lung and Skin was less than in Thyroid. The maximum of absorbed dose in Thyroid was at 1 mci activity of I-131. However, the effect of 1 mci in other organs around Thyroid was still less that it was not really influential for the organs.