Characteristics Analysis And Design Optimization Of Ionization Chamber For Proton Therapy Beamline

Based on the dose distribution characteristics of the Bragg peak,proton therapy has currently become the advanced precision cancer treatment method.The beam diagnostic system can obtain the beam characteristics of the accelerator and the beamline,which is the foundation for debugging and ensuring the normal operation of the proton therapy facility.For critical position and cross-section information of the proton beam,since the intensity of the therapeutic proton beam is in the order of nanoamperes,it is difficult for traditional inductive probes to output sufficient signal strength,and a high-sensitivity ionization chamber based on the gas ionization effect is required for measurement.In this paper,the characteristic analysis and structural optimization design of the insertable ionization chamber used in the HUST-PTF proton therapy facility under study at Huazhong University of Science and Technology is carried out,and the test of the electronic system of the ionization chamber is carried out.The main contents include:(1)The detection performance of the ionization chamber was studied.In order to determine whether the electrons generated by the ionization of protons in the gas medium can accurately reflect the distribution of incident protons,this paper studies the edge effect of the electric field in the ionization chamber,calculates the effect of the edge effect on particle collection,and compares the electron and proton distribution,proving the feasibility of using electron distribution to calculate the proton distribution;the ionization chamber will affect the parameters of the proton.In this paper,the process of proton passing through the ionization chamber is simulated in Geant4,and the beam loss,energy loss and emissivity changes of the proton are obtained.(2)At present,the distance between the center of the strips of the ionization chamber is 1mm,the number of strips is large,the front-end electronics is complicated,and the production cost is high.In this paper,Garfield++ and Matlab are used to simulate the particle collection process on the strip of the ionization chamber.Through the comparison of the measurement accuracy of the beam position and size,the optimized strip parameters are obtained.Without reducing the measurement accuracy,the center distance between the strips of the ionization chamber is increased,and the cost of the ionization chamber is reduced.(3)While the production of the ionization chamber prototype for the HUST-PTF gantry section is completed,the front-end electronic performance needs to be tested to determine whether it meets the design requirements.This paper first introduces the electronics testing facility;due to manufacturing errors and other factors,the front-end electronics has different amplification factors for different strip signals,which will affect the quality of the reconstructed image.Therefore,the amplification factor of each strip is measured,which provides a basis for later correction;in addition,the linearity of each channel and the repeatability of the output signals are also analyzed.