Design And Development Of Scintillation Fiber Dosimeter And Dose Simulation Of Brachytherapy

With the development of radiotherapy technology,the complexity of radiotherapy is increasing.In the course of radiotherapy,especially in brachytherapy,direct real-time monitoring of tumors and organs at risk with high position resolution is the most direct and effective method for dose verification and optimization of treatment plans,and risk assessment of healthy tissues.This article has developed a set of plastic scintillation fiber dosimeter(PSFD)based on SiPM current readout.Due to its excellent performance in position resolution,tissue equivalent,remote operation,and real-time measurement,the dosimeter has great advantages in high position resolution interventional dose measurement in brachytherapy.This task will focus on the dose distribution characteristics of 192Ir source,the design and development of PSFD,and the simulation research of application of PSFD in brachytherapy.The major research contents and results are presented as follows:(1)The Monte Carlo N-Particle Transport Code(MCNP)was used to simulate the dose distribution characteristics of medical 192Ir sealed sources to provide theoretical guidance for the development of dosimeter.The results show that the dose distribution in the near-field area of the 192Ir sealed source is obviously anisotropic,with the difference of 11.8%.In different media,the dose fell in inverse relationship with the square of the distance.The difference of dose distribution between water and soft tissue is less than 0.8%,and the difference with bone is less than 2.3%.The spatial dose distribution of 192Ir body source and point source in the air was calculated using the repeated cards of U(universe)and FILL,and the spatial dose was reconstructed in three dimensions using MATLAB algorithm.The 192Ir point source iso-dose rate surface has a spherical distribution and the body source has an "apple-like" distribution.At the same location,the point source dose rate is higher than body source.(2)Based on the above dosimetric characteristics,a highly position-resolved plastic scintillation fiber dosimeter based on SiPM current readout was designed and manufactured.The dosimeter consists of a plastic scintillating fiber probe,a transmission fiber,a photoelectric conversion device,and a data acquisition system.After the production of the dosimeter is completed,the basic performance of the dosimeter is tested.The results show that the dosimeter is excellent in stability and repeatability,and it changes linearly in the range of 10cGy/min?9000cGy/min,which meets the demands of general clinical dose measurement.The dosimeter can be used for relative dose measurement,but when the ray energy is too low,the measurement error increases.The dosimeter is susceptible to ambient temperature and bending of the transmission fiber when it is working.If the accuracy of the dose measurement is controlled within ± 1%,the temperature drift should be less than 1°C,and the radius of curvature of the white fiber with a diameter of 1mm will be greater than 11cm.(3)MCNP was used to simulate the scene of PSFD used in afterloading dose measurement,and the water equivalence and energy response characteristics of PSFD were studied.The results show that the plastic scintillation fiber performs well in terms of water equivalence,especially in the photon energy range of 0.2MeV?6MeV,but the detection sensitivity of plastic scintillation fiber decreases at the low energy end.PSFD has good energy response characteristics whenmeasuring doses in the near-field area(<10cm)of the 192Ir source,but they show energy dependence when measuring doses in the far-field region(>10cm).In this subject,a set of high-position-resolved and real-time monitoring plastic scintillating fiber dosimeter based on SiPM current readout has been developed.The work offers a feasible solutions for continuous beam dose measurement.The simulation research on the water equivalence and energy response of PSFD applied to afterloading dose measurement has supply experience for the application of dosimeter to actual dose measurement.