Research On Beam Delivery System And Treatment Planning Of Heavy Ion Medical Machine Based On Monte Carlo Code

Due to its superior depth-dose distribution and high relative biological effect,heavy ion beam radiotherapy has become the most advanced,most scientific and most effective radiotherapy method in the world.Although rapid advances in radiotherapy techniques have reduced the uncertainty of radiotherapy,there are many uncertainties in particle therapy due to the positioning error,range struggling,incident particle error and other factors,and studying and overcoming these uncertainties can provide a more accurate treatment.We investigated and analyzed the main factors influencing the physical and biological processes and uncertainties of particle therapy,and found that the uncertainties in the treatment planning system and dose delivery had the greatest impact on the overall clinical outcome.In addition,the spot scanning beam delivery system is particularly sensitive to these uncertainties because of its particularity.In view of this,an active beam delivery system of HIMM was established with FLUKA Monte Carlo code in this paper,and the simulation and optimization of key problems in beam delivery system and treatment planning of HIMM were carried out.(1)The influence of the uncertainty of the beam delivery system on the beam uniformity and penumbra was studied.Firstly,the percentage depth dose curves and lateral dose distribution at Bragg peak of 190 Me V/u and 260 Me V/u carbon ion beams were simulated and measured by FLUKA Monte Carlo code and experiment,respectively.Considering the contribution of low-dose envelope to the spatial dose distribution of carbon ion pencil beam,different pencil beam models are used to simulate the transverse dose distribution of carbon ion beam at different depths;Secondly,the dose uniformity and penumbra of treatment area are simulated when there are dose value accuracy error and spot position error in the process of beam delevery.The results show that the simulation results of FLUKA are in good agreement with the measurement results.Compared with the double Gaussian model,the double Gaussian logistic model can simulate the spatial distribution of pencil beam better and is more sensitive to the dose value accuracy error and spot position error in the field.(2)mat RAD,an open source treatment planning software,was used to simulate and optimize treatment planning system for head tumors.The physical basic data of the active scanning treatment nozzle is implanted into mat RAD to analyze the effects of biological model,spot spacing and set-up on treatment planning.The results show that there is little difference in the dose distribution calculated by the two different biological effect models.The conformal index of the treatment plan and the uniformity of dose distribution in the target area were better than that in the spot size of 5 mm when the spot spacing was less than 5 mm.When there is a large error in the patient's positioning,it will lead to a serious deviation in the dose distribution.(3)The FLUKA Monte Carlo code was used to build the adult man phantom model based on ICRP110 and the voxel model of Chinese male.The active beam delivery system was used to simulate the dose distribution and energy deposition of the human body.At the same time,the absorbed dose changes of different tissues and organs when the positioning error of the human body appeared were also simulated.The results show that there is no significant difference in absorbed dose between ICRP110 adult human model and Chinese male voxel model in active beam delivery system.When there is a set-up error,the absorbed dose of adjacent tissues will be different,which suggests that we should try our best to avoid direct exposure to radiation sensitive tissues and organs.The research of this paper is helpful for medical physicists to have a deeper understanding of the process of radiotherapy,provide important clues for the fine debugging of radiotherapy,and provide reference for optimizing the radiotherapy planning system.Through the analysis of a series of errors,it is very important to improve the robustness of radiotherapy planning and further develop more accurate point scanning technology.