Feasibility of the Compton Suppressed Gamma-ray spectrometry for proton therapy applications

Abstract

The presence of the Bragg peak and its use in proton therapy cause less damage to healthy tissues. For optimal use of the proton beam in proton therapy, it is necessary to monitor the deviation of its range during treatment. The prompt gamma rays originated from the nuclear reactions of the proton beam with tissue elements can be applied for this purpose. The spatial distribution of prompt gamma rays can be used to estimate the range of the incident charged particles. Detecting a wide energy range of gamma rays, up to 10 MeV, is the most challenging step of the proton dose verification by using prompt gamma spectroscopy. Compton suppression is a system that is used to reduce the contribution of scattered gamma rays. This technique will cause better detection of the peaks of low-energy prompt gamma rays. In this research, the performance of a Compton suppression system has been investigated in two fields for proton therapy and for elemental analysis of materials using isotopes by a wide range of gamma energies. At first, by using the simulated Compton suppression system, the calculations of the prompt gamma ray spectra emitted from the brain phantom during the radiation of 150 MeV protons were presented. The results indicated that the low energy elements peaks such as 40Ca (1.37 MeV) with CSF equal to 1.138 appeared in the suppressed spectrum. Also, it was possible to detect 14N (2.31 MeV) and 16O (6.13 MeV) peaks equivalent to the CSF 2.449 and 2.067 respectively. In the next step, it was possible to detect the low energy peaks of 152Eu and 155Eu isotopes in the suppressed spectrum. For this purpose, the minimum relative intensity required to detect all 152Eu and 155Eu peaks was equivalent to 0.001 and 0.002 respectively. CSF for the lowest energies such as 105 keV and 344 keV was equal to 1.169 and 1.184. The simulation was done using the GEANT4 Monte-Carlo toolkit.