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A systematic Monte Carlo study of secondary electron fluence perturbation in clinical proton beams (70–250 MeV) for cylindrical and spherical ion chambers
Author(s) -
Verhaegen Frank,
Palmans Hugo
Publication year - 2001
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.1406519
Subject(s) - fluence , ion , proton , atomic physics , electron , monte carlo method , secondary electrons , radius , materials science , physics , nuclear physics , statistics , mathematics , computer security , quantum mechanics , computer science
Current dosimetry protocols for clinical protons do not take into account any secondary electron fluence perturbation in ion chambers. In this work, we performed a systematic study of secondary electron fluence perturbation factors for spherical and cylindrical ion chambers in proton beams (70–250 MeV). The electron fluence perturbation factor, p e , was calculated using Monte Carlo transport of protons and secondary electrons. The influence of proton energy, cavity wall material (graphite, water, A150, PMMA, polystyrene), cavity radius, cavity wall thickness and positioning depth in water is studied. The influence of inelastic nuclear proton interactions is briefly discussed. It was found that p edepends on wall material; the largest values for p ewere obtained for ion chambers with A150 walls( p e= 1.009 ) , the smallest values for graphite walls. The perturbation factor was found to be largely independent of proton energy. A slight decrease of p ewith cavity radius was obtained, especially for low energy protons. The wall thickness was found to have no effect on p ein the range studied (0.025–0.1 cm). The depth of the cavity in a water phantom was also found to have an insignificant effect on p e . Based on the results in the paper for spherical and cylindrical ion chambers, a method to calculate p efor a thimble ion chamber is presented. The results presented in this paper for cylindrical and spherical ion chambers are in contradiction to the calculated electron fluence perturbation factors for planar ion chambers in the paper by Casnati et al.