ABSTRACT
Compton imaging is an imaging technique in which Compton scattering is used to produce images from a gamma-ray source. Compton imaging systems are also known as Compton camera. The basic design of Compton imaging systems consists of two-position detectors that are sensitive to the position and energy scattered from gamma rays. Compton camera efficiency is defined as the fraction of photons entering the scatterer (disperse) detector that undergoes only one Compton scattering and is then photoelectrically absorbed in the absorber detector. In the present study, the efficiency of a Compton camera was investigated based on semiconductor detectors using the GEANT4 simulation toolkit. In this study, the sensitivity of the efficiency of the Compton imaging systems to the distance between the source and the scatterer detector, the distance between the two detectors, dimensions, and thickness of the absorber and scatterer detectors, number of scatterer detectors with different thicknesses, the energy of radioisotope of the source, and semiconductor's type in the scatterer and absorber detectors were performed. To this end, the Compton camera was modeled using the GEANT4 simulation toolkit. In addition, the code was developed in C++ to get the correct events of efficiency in the Compton camera. The simulation model includes the details of the detector geometry, detector segmentation, and energy discrimination levels of the scatterer and absorber. According to the results, 11C has the maximum efficiency as a radioactive source."GaAs" and "Ge" as the scatterer detector and "CdTe" and "HgI2" as the absorber detector are the best choices. According to the results, the shorter the distance between the source and the two detectors, the higher the efficiency of the Compton camera. Of course, this distance must be selected according to the application used. According to the results in the research, with increasing the dimensions of the scatterer detector plate, the amount of efficiency increases up to the dimensions of the absorber detector plate, but a size larger than the absorber detector, it reaches a degree of saturation. Also, by increasing the thickness of the scatterer detector, the efficiency first increases and then reaches the maximum value and then decreases, and increasing the thickness of the absorber detector increases efficiency. The results of the simulation in the present paper have an acceptable agreement with the experimental several types of research in the world. The results of this simulation can be considered for the design of Compton cameras.
ABSTRACT
AIM: Evaluation of energy deposition of protons in human brain and calculation of the secondary neutrons and photons produced by protons in proton therapy. BACKGROUND: Radiation therapy is one of the main methods of treating localized cancer tumors. The use of high energy proton beam in radiotherapy was proposed almost 60 years ago. In recent years, there has been a revival of interest in this subject in the context of radiation therapy. High energy protons suffer little angular deflection and have a well-defined penetration range, with a sharp increase in the energy loss at the end of their trajectories, namely the Bragg peak. MATERIALS AND METHODS: A slab head phantom was used for the purpose of simulating proton therapy in brain tissue. In this study simulation was carried out using the Monte Carlo MCNPX code. RESULTS: By using mono energetic proton pencil beams, energy depositions in tissues, especially inside the brain, as well as estimating the neutron and photon production as a result of proton interactions in the body, together with their energy spectra, were calculated or obtained. The amount of energy escaped from the head by secondary neutrons and photons was determined. CONCLUSIONS: It was found that for high energy proton beams the amount of escaped energy by neutrons is almost 10 times larger than that by photons. We estimated that at 110 MeV beam energy, the overall proton energy "leaked" from the head by secondary photons and neutrons to be around 1%.
