Design And Research Of Rapid Quality Assurance Fluorescence Detector Device For Therapeutic Performance Measurement Of Heavy Ion Beam

Ion beams(protons and heavy ions)have the advantages of inverted depth dose distribution and high relative biological effectiveness in Bragg peak region,which is regarded as the most ideal radiotherapy ray in the 21 st century.In proton/heavy ion therapy,the accuracy of ion beam energy(range)is directly related to the safety and effect of treatment,such that range verification is an important quality assurance item in particle radiation therapy.In this paper,the vertical depth dose distribution(Bragg curve)of an ion beam is able to be converted to a lateral dose profile by means of a wedge device.The depth information is converted into lateral two-dimensional distribution information,which is conducive to uniform rapid measurement method.At the same time,aiming at range verification and transverse beam field measurement,a beam fast QA device was developed based on two-dimensional fluorescence detection method,which realized multifunctional fast measurement,and was beneficial to improve the efficiency of ion therapy QA verification.Firstly,the GEANT4 kernel-based GATE Monte Carlo simulation platform was used to calculate the depth dose distributions of various energy carbon-ion beams in materials of copper(Cu),aluminum(Al),iron(Fe)and polymethyl methacrylate(PMMA),which were usually applied to make wedge devices.The relationships between the beam energy and corresponding penetration depth of the Bragg peak position for the carbon ion beams in the various materials were obtained.The lateral dose profiles of carbon ion beams with different energies passing through a single wedge plate,a double wedge plate,and a large and small combined wedge plate were simulated and calculated under different configurations.Therefore,the relationships between the position of the peak of lateral dose and the beam range for the various energy carbon ion beams were acquired.The above Monte Carlo simulation study provided a basis for further development of rapid range verification methods and devices in heavy ion therapy.Secondly,the beam rapid QA device was built based on the two-dimensional fluorescence detection method,and combined with the dual-wedge device,which aimed to develop methods and techniques for rapid verification of the range of carbon ion beams.On the premise that the simulation results provided a strong foundation,this paper showed the relative lateral dose distributions obtained from the CMOS camera in the scintillator detection system under the condition of carbon ion beams with different energies passing through the double wedge device and the scintillator detection system,and then compared the simulation results obtained by the GEANT4 kernel-based Monte Carlo(MC)simulation platform.In this condition,by calculating the position corresponding to the peak of the lateral dose distribution,the range of the carbon ion beam was able to be effectively verified,and the efficiency of the range of the carbon ion beam about routine QA verification could be improved.Finally,based on the basic technical analysis of the scintillator detection system,the feasibility of its application in the measurement of transverse radiation field of ion beam is verified by experiments.Under the active beam distribution system,this paper tested the position of the beam spot formed by the pencil beam scanning in the scintillation detection system,and compared it with the result acquired from the GAFCHROMIC EBT3 film,which verified the accuracy of the position of spot beam in the scintillation fluorescence detection system.Under the passive beam distribution system,the carbon ion beam was irradiated to form a uniform field,and the scintillator detection system was used to dose calibration and reverse dose verification for different radiation doses under the same conditions.After that,the results verified the accuracy of the scintillator detection system in the dose measurement through comparing with the dose measurements of the EBT3 film.In addition,in the uniform irradiation field formed by carbon ion beam,the flatness of the field of scintillator detection system and EBT3 film was compared,which proved that the scintillator detection system could accurately be used to test the flatness of the field.The results of this study indicate that the scintillator detection system has the ability to rapidly and accurately monitor the beam properties before radiation therapy,and is an effective technical means to improve the efficiency of QA validation in heavy ion therapy.This study provides a solid foundation for the further development of rapid quality assurance methods and equipment for heavy ion therapy.