Monte Carlo Simulation Of Proton And Carbon Ion Therapy For Cancer

Radiotherapy plays an increasingly important role in cancer treatment.With the advancement of accelerator technology,the beam currents used in radiotherapy are becoming more and more widely used.From the initial X-ray therapy machines and isotope radiation sources,the emergence of medical electron accelerators,to the increasingly widely used proton and heavy ion accelerators,doctors have more options to provide patients with more suitable radiotherapy plans.Heavy ion therapy has good safety and biological effects in cancer treatment.Before using heavy ion radiotherapy,the Monte Carlo method can be used to simulate the dose of the beam deposited in the tissue,so that a sufficient dose can be deposited in the tumor target area,and at the same time,the damage to the normal tissue can be minimized.The main research contents of this paper include:（1）Research on the radiotherapy process of proton and carbon ion therapy with GATE software;（2）Analyze the yield ofβ+radionuclides in the process of radiotherapy,and generate the relationship between the activity distribution and dose distribution of newβ+radionuclides,and the change ofβ+radionuclide activity with treatment time,etc.;（3）Use the weight function fitting method to study the Spread-Out Bragg Peak（SOBP）and dose distribution characteristics,and analyze the lateral dose spread;（4）Simulation of proton,heavy ion therapy and In-beam PET.A variety of positron nuclides are produced during proton and heavy ion radiotherapy.In carbon ion therapy,positron nuclide contributes the most to¹⁰C;and proton therapy contributes the most to¹⁵O.The positron nuclides deposited in the target body during radiotherapy are related to the dose distribution.For carbon ion therapy in the depth direction,the least squares method was used to perform polynomial fitting on the peak position of the activity curve and the peak position of the dose curve,and the relationship between them was found.The calculation results show that the carbon radio therapy result coincide after fitting,while there is a small deviation for proton therapy.The position of the dose peak can be accurately monitored by measuring the activity distribution in the target by In-beam positron emission tomography（In-beam PET）.The peak of the activity curve in the depth direction is not obvious for proton therapy.In order to investigate the influence of the ion beam quality on the dose distribution,the cross-sectional standard deviation.Energy standard deviation and beam intensity of the carbon ion beam were changed,and the effect on the transverse dose distribution was studied.It is found that the cross-section standard deviation has the greatest influence on the transverse dose distribution.The energy standard deviation has almost no effect.The beam intensity is halved.The maximum dose peak value is halved.and the half-height width of the dose curve has no obvious effect.Monoenergetic beams can only generate one Bragg peak in a homogeneous material and cannot fully adapt to the geometry of the tumor.In clinical practice,a broadened Bragg peak is usually used to match the tumor shape.In this paper,the Bragg peak broadening is studied using the weight function fitting method.According to Geiger’s law,the values ofαand p in the human abdomen model were determined.By changing the fitting coefficient of the broadened Bragg peak,according to the Monte Carlo simulation and the correction function F（R）,which were used to compensate for the combined effects of ion scattering and other effects,the weight function adaptation method can quickly obtain the specified interval SOBP.Simulate proton and carbon ions with different energies to irradiate the human body by Monte Carlo simulation method,and to calculate the yield of¹⁰C,¹¹C and¹⁵O,as well as their spatial distribution in the human body.Then this kind of nuclide was used as the radiation source to complete the In-beam PET imaging simulation.The distribution characteristics of positron nuclides on the particle incidence path were obtained,which was helpful to achieve the dose monitoring in clinical radiotherapy.