Monte Carlo Simulated The Dose Distribution And Radiation Protection Of ¹⁹²Ir Source

In recent years, with the development of medical technology, radiation therapy becomes more and more important in cancer treatment. However, radiation therapy on the human body is certain hazards, which requires exact protection. Today, modern facilities are equipped with high-dose-rate (HDR) installations where a shielded room is specifically designed for exclusive use with HDR applications. Usually, Iridium-192 sources are used in HDR brachytherapy for the treatment. In order to avoid harming in the treatment, simulation on dose distribution of Iridium-192 is very important.Monte Carlo (MC) methods have been used for many decades to simulate radiation transport in matter. MC is a term used to describe a universal numerical method, based on stochastic sampling that can predict a reliable solution to complex problems in many areas of science, by subjecting them to a game of chance. As such, it has found increased number of applications in the fields of medical and radiation physics.This article studies the practical problems from Tumor Hospital of Harbin brachytherapy. Before doing this research, the dose distribution is calculated by MCNP 4C. The MCNP 4C flux calculation can be better to calculate absorbed dose compared with energy deposition, and this method is also very convenient. A example is simulated: a 1 mCi 137Cs point source, the results of MCNP 4C simulation and theoretical calculation is same. So the Monte Carlo dose distribution simulation is reliable.In order to obtain a standard deviation of the mean, which is less than 5%, the model and tally of Monte Carlo simulation are simply. To score kerma, the cubic lattice with a side length of 10cm was used, which is filled in the layer(Z=130cm) of the brachytherapy room. In kerma graph, the dose distribution can be seen clearly. In the same way, to draw 3D dose graph of the Iridium -192 sources at 1Gy / h, which is drew by the MATLAB software.The door of the brachytherapy room is very important in sheltering the radioactive ray, so the dose distribution near the door is simulated, and the result of simulation indicates that a lead door (5mm) must be built to shelter the radioactive ray leaking out of the door. And the dose outside the walls is also simulated, the results indicates that it is below the radiation safety standards.To achieve the better design of the west wall(the original design is 50cm), reduce the thickness (40cm, 30cm, 20cm) of the wall, and find out the suitable case. From simulating dose data outside the wall, when the thickness of the wall at 20cm, part of the dose exceeded the value of radiation safety standards, and at 30cm and 40cm,the dose are security, so the thickness of the Western Wall could be appropriate to select between 30cm and 40cm.