Monte Carlo Simulation Study On Over-Response And Dose Perturbation Of Embedded Fiber X-ray Detector

Radiotherapy is a commonly used method in the current cancer treatment process.The development of radiotherapy technology has new requirements for detectors.For example:the detector needs to be miniaturized,real-time detection,and even the ability to detect doses in vivo.Traditional dosing equipment has many shortcomings in dealing with the new technology of radiotherapy.At present,the equipment with potential advantages is mainly fiber-optic dosimeters.Since fiber-optic dosimeters are mainly used for experimental research under the platform of medical linear accelerators,they are also called fiber X-ray detectors or fiber X-ray sensors.The fiber X-ray detector is a dose detection device that expresses the dose information as a fluorescent signal.The working principle of the fiber X-ray detector is that the signal collection end collects the fluorescent photons released by the scintillator after being irradiated.The equipment for the collection process mainly includes transmission fibers and photon counters.Currently,fiber X-ray detectors using inorganic scintillators are a research hotspot in the field of fiber optic dosimeters.However,the occurrence of over-response phenomenon is the main reason hindering the practical application of optical fiber X-rays using inorganic scintillators.The cause of the over-response phenomenon is not yet conclusive.This paper aims to explore the causes of the over-response phenomenon of fiber X-ray detectors by using Monte Carlo simulation.The probe part of the fiber X-ray detector is mainly composed of PMMA fiber and scintillation material Gd₂O₂S:Tb.In this paper,the Monte Carlo simulation tools EGSnrc and GEANT4 call the phase space file provided by the International Atomic Energy Agency（IAEA）to irradiating the fiber optic X-ray detector located in the water phantom,and extract a series of information.By comparing the simulation results with the previous simulation results,this paper believes that the non-linear response of inorganic scintillators is one of the reasons for the over-response phenomenon of fiber X-ray detectors.By establishing the region of interest and analyzing the changing trend of the number of X-rays that affect the fiber X-ray detector,this paper believes that the second reason for the over-response phenomenon is the indirect energy deposition of low-energy X-rays on the inorganic scintillator.This paper explores the influence of the size of the scintillator on the performance of the optical fiber X-ray detector by simulating the use of different sizes of inorganic scintillators in fiber optic X-ray detectors.The simulation results show that when the field is small,the optical fiber X-ray detectors with different volumes of scintillators have a clear degree of discrimination,but when the field is large,the degree of discrimination is not obvious.In addition,this paper also simulated the deposition energy on the plane of the fiber X-ray detector located at a depth of 1.5 cm.This simulation is used to explore the perturbation of the surrounding energy deposited by the fiber optic X-ray detector using Gd₂O₂S:Tb material.By using Monte Carlo to simulate the fiber X-ray detector using the inorganic scintillator Gd₂O₂S:Tb,the simulation results of this paper show that the fiber X-ray detector with embedded structure has better performance in the field of medical dose detection.And,the detector has a better application prospect.