¹²⁵I Dose Calculation Based On Monte Carlo Method And Related Optimization Of Radiotherapy Plan

Cancer is a major disease that threatens people’s health.More than half of patients with malignant tumors require radiation therapy.At present,the type 6711¹²⁵I radioac-tive source is one of the effective means for the treatment of tumors.It is widely used in the treatment of lung cancer,prostate cancer,head and neck cancer and other cancers.The brachytherapy using¹²⁵I is An emerging and effective radiation therapy.In order to ensure the efficacy of radiotherapy in clinical practice,it is necessary to formulate and optimize the radiotherapy plan in advance,and studying the dose distribution of multiple¹²⁵I sources in three-dimensional space is the prerequisite for formulating a radiotherapy plan.This paper simulates and compares the dose distributions of multiple¹²⁵I sources in the water phantom in different distribution modes.The main work of this article is as follows:1.Use the two Monte Carlo software MCNP5 and TOPAS to model the radiation source to simulate the surrounding 1.5cm³ according to the shape,material and decay characteristics of the single 6711 type¹²⁵I source in the relevant papers Dose distribution in the water phantom within.2.After completing the modeling,repeat the simulation to take the average value to obtain the final dose data results.And the dose data obtained from the simulation,using the formula in the TG-43U1 report,calculate the corresponding radial dose function and anisotropic function,and compare it with the standard value to confirm whether the obtained dose is accurate.3.Using MATLAB software,the dose distribution data of single and multiple¹²⁵I radioactive sources in the water phantom are visually displayed.At the same time,in order to compare the effects of different radioactive source distributions on the dose distribution,the formula of dose volume histogram and the calculation of dose volume histogram evaluation index F is introduced.By comparing the value of F,the uniformity gap of dose distribution under different distribution methods is directly compared.4.This article compares the F after implanting 4 radioactive sources at different distances.The F value when the distance between the radioactive sources is 1cm is higher than the F value when the distance is 0.8cm and 1.2cm,and it is also compared.F after implanting 3 radioactive sources at different distances,the F value when the distance between the radioactive sources is 1cm is 7%higher than the F value when the distance is 0.8cm and 1.2cm.This paper also compares the F of 9 radioactive sources implanted in accordance with the equidistant distribution and the peripheral distribution.The F value of the peripheral distribution is about 30%higher than that of the equidistant distribution.The F value of the distribution is more than 50%higher than the F value of the 17 radioactive sources distributed at equal intervals.In this paper,based on the Monte Carlo method,the dose distribution of the6711 type¹²⁵I source obtained using MCNP5 is basically accurate,that is,the axis is symmetrical along the axis,and at the same distance,the sandwich between the axis and the axis Where the angle is larger,the dose is larger,and the dose distribution at both ends of the shaft has a more obvious depression.It is concluded that the distance between the radioactive sources should be about 1 cm,and that the distribution of the radioactive sources should be peripheral.