Research On Key Techniques Of On-line And Real-time Boron Concentration Monitoring System For Boron Neutron Capture Therapy

Nowadays,cancer has become the biggest killer and high mortality rates in China.As one of the three major cancer treatment method,Radiation therapy(RT)has been relentlessly pursuing high precision,high efficiency,and low side-effects.Boron Neutron Capture Therapy(BNCT)technology,as a special type of RT,was developed rapidly with the development of accelerator technology.However,on-line and real-time boron concentration monitoring in BNCT is a key technical difficulty for accurate dosimetry assessment.This thesis foucus on the PG-SPECT system development for boron concentration monitoring,which is based on the 478 ke V prompt ? ray emitted during BNCT treatment.A number of key technical issues in the PG-SPECT system were studied.The main research contents and results are as follows,(1)The theoretical feasibility of PG-SPECT system for on-line and real-time boron concentration monitoring in BNCT was validated using Monte Carlo simulation.The prompt ?-ray emission from soft tissue in BNCT was studied using MCNP and Geant4.Results show that the Geant4 and MCNP can produce similar amount of prompt gamma rays,and therefore the accuracy of Geant4 simulation to produce prompt ?-ray yield was verified.The PG-SPECT system based on the mechanical collimator was used to detect the 478 ke V prompt ? rays from brain tumors in BNCT treatment,and then the tumors in a patient were discussed through the reconstructed image with MLEM reconstruction algorithm.The results show that it is feasible to realize on-line and real-time boron concentration monitoring using PG-SPECT system based on the 478 ke V prompt ?-ray imaging.(2)The thermal column of TRIGA Mark II reactor was optimized with Monte Carlo simulation particularly for experimental verification of on-line and real-time boron concentration monitoring based on PG-SPECT system.Four optimization configurations were explored through the quantification of thermal neutron fluxes and ? fluxes in the beam port and the detector position.Results show that 30 cm length nature lithium polyethylene(4 cm in diameter for beam port)has the best performance,and the thermal neutron flux on beam port is 6.08 × 107 #/(cm2·s).The thermal column of reactor has been modified based on the optimized design in pavia TRIGA Mark II reactor.(3)The experimental study of the CZT detector for PG-SPECT system was carried out on the modified thermal column of TRIGA Mark II reactor.The basic performance characterization of the CZT detector was explored through the Monte Carlo simulation and experimental measurement.For the energy of 511 ke V photon,which is close to the 478 ke V prompt gamma,the energy resolution of the CZT detector is 4.01%.The experimental results show that the 478 ke V generated in the BPA sample was successfully detected by the 5 × 5 × 20 mm~3 CZT detector under the condition of BNCT treatment.Therefore,the feasibility of PG-SPECT system based on CZT detector used for on-line and real-time boron concentration monitoring in BNCT was experimentally verified.(4)Furthermore,the PG-SPECT system based on Compton camera was proposed to perform online and real-time boron concentration monitoring in BNCT.A Si/Ge Compton camera for BNCT was optimized by the Geant4 simulation.Then the performance of the Si/Ge Compton camera was evaluated using Monte Carlo method and the LM-MLEM reconstruction algorithm,which verified the theoretical feasibility of the PG-SPECT system based on Compton camera.As a resut,the optimized Si/Ge Compton camera was consisted of a 3 cm thick and 10 cm wide Si scattering detector and a 10 cm thick and 10 cm wide Ge absorption detector.The distance between the two detectors is 1 cm.For melanoma tumors treated by BNCT,the Compton camera was used to detect the 478 ke V promt ? rays,and the LM-MLEM reconstruction algorithm was used to reconstruct the images from the detected results.The results show that it is feasible to realize on-line and real-time boron concentration monitoring using PGSPECT system based on Compton camera.With the increase number of detection angles of Compton camera,the image artifacts are remarkably reduced and the reconstruction images obtained are more accurate.Moreover,a GPU-based parallel reconstruction acceleration program based on Open GL was developed,which largely reduces the reconstruction time.Overall,this work will provide theoretical support and experimental reference for the boron concentration monitoring technology based on prompt ? ray in BNCT.This work will promote the clinical translation of the PG-SPECT system for on-line and real-time boron concentration monitoring during BNCT treatmrnt.Eventually,this work will provide technical support for the precise and efficient BNCT.