PET Dose Verification Study Of Carbon Ion Tumor Radiotherapy Based On TPS And MC Calculation

Carbon ion beam has many advantages,such as high cytotoxicity,reversed dose distribution,high energy transfer linear density and high relative biological effect,and has been used in clinical treatment of malignant tumors.The dose distribution accuracy of clinical radiotherapy for carbon ion tumor determines the therapeutic effect and survival rate of patients,and the dose verification is an important link in the treatment process.Positron emission tomography（PET）,as an important means of non-invasive monitoring in radiotherapy,can monitor the position and dose distribution of Bragg peak of carbon ions in time,which has potential application value.In this study,the carbon ion accelerator beam delivery system and PET scanning system were modeled by combining ci Plan（TPS）,Monte Carlo simulation software GATE and actual measured values,and the dose distribution and PET imaging were compared.In point scanning beam distribution system,the single energy beam integral dose distribution curve calculated by MC and measured by experiment is consistent with the peak position,peak plateau ratio and beam half height width to ensure the accuracy of MC modeling and beam parameters.To further verify the accuracy of monte carlo simulation,TPS was used to design radiotherapy plan,and the dose distribution calculated by TPS and MC was compared.The linear quadratic model（LQ）model was used to calculate the biological dose.The mean errors of MC simulation and TPS dose distribution of physical dose and RBE weighted dose in SOBP were within0.89 % and 1.36 %,which were within the range of clinical treatment acceptance.A sensitive 1-meter whole-body PET model was used for in-beam real-time imaging analysis.There is a location difference between PET imaging and biological dose distribution in the direction of beam,which is related to energy.When using the dose broadening area of tumor area of 60 mm,there is a quadratic increasing relationship between PET imaging and biological dose location difference and energy,and the dose distribution in tumor area of beam direction and PET imaging location difference are within 3-8 mm.CT images were used as 3D human body models to design and calculate the dot scan radiotherapy plan,considering the decay process of dot scan.The maximum location difference between PET imaging and RBE weighted dose in tumor region in beam direction was within 10 mm,and the maximum location difference between PET imaging and RBE weighted dose in BEV direction was within1 mm.In-beam PET,as an important means of noninvasive field monitoring of tumor radiation therapy,can timely monitor Bragg peak position and dose distribution,and has potential application value for real-time imaging of dose distribution.