A comparison of the measured responses of a tissue-equivalent proportional counter to high energy heavy (HZE) particles and those simulated using the Geant4 Monte Carlo code

Abstract

Monte Carlo simulations of heavy ion interactions using the Geant4 toolkit were compared with measurements of energy deposition in a spherical tissue-equivalent proportional counter (TEPC). A spherical cavity with a physical diameter of 12.7 mm was filled with propane-based tissue-equivalent gas surrounded by a wall of A-150 tissue-equivalent plastic that was 2.54 mm to thick. Measurements and Monte Carlo simulations were used to record the energy deposition and the trajectory of the incident particle on an event-by-event basis for ions ranging in atomic number from 2 ( 4 He) to 26 ( 56 Fe) and in energy from 200 MeV/nucleon to 1000 MeV/nucleon. In the simulations, tracking of secondary electrons was terminated when the range of an electron was below a specified threshold. The effects of range cuts for electrons at 0.5 μm, 1 μm, 10 μm, and 100 μm were evaluated. To simulate an energy deposition influenced by large numbers of low energy electrons with large transverse momentum, it was necessary to track electrons down to range cuts of 10 μm or less. The Geant4 simulated data closely matched the measured data acquired using a TEPC for incident particles traversing the center of the detector as well as near the gas-wall interface. Values of frequency mean lineal energy and dose mean lineal energy were within 8% of the measured data. The production of secondary particles in the aluminum vacuum chamber had no effect on the response of the TEPC for 56 Fe at 1000 MeV/nucleon. The results of this study confirm that Geant4 can simulate patterns of energy deposition for existing microdosimeters and is valuable for improving the design of a new generation of detectors used for space dosimetry and for characterizing particle beams used in hadron radiotherapy.

Microdosimetry of radiation field from a therapeutic 12C beam in water: A study with Geant4 toolkit

“…In table 5 the results for the TEPC placed at "0 cm, plateau" at the depth of 52.1 mm in water under the impact of 3 mm FWHM beam at the entrance of the phantom are presented, cases (1a), (1b), ( 1c) and (1d). At this TEPC position the energy of 12 C at the entrance to the TEPC volume is estimated as ∼ 218A MeV, and it is close to the beam energy (220A MeV) used by Taddei et al for homogeneous irradiation of a similar TEPC, but surrounded by air (Taddei et al 2008). The thickness of the TEPC wall was twice as large (2.54 mm) compared to the TEPC used at GSI, and their TEPC operated at different tissue-equivalent gas pressure (effective diameter of 3 µm).…”

“…Calculations with various physics settings are marked by letters: (a) -default MCHIT physics, (b) -the Penelope model for electrons, (c)without simulation of δ-electrons, (d) -without simulation of nuclear fragmentation. Experimental data (Martino et al 2010), ( 1) and (Taddei et al 2008) also explains the value of ȳf calculated for the conditions of the second experiment, but with central incidence of 12 C nuclei on TEPC, case (2a). There the beam fragmentation outside the TEPC is negligible as it is surrounded by air.…”

“…In these measurements and calculations the dependence of ǫ on the impact parameter of the ion track was investigated in detail. As demonstrated by Taddei and coauthors (Taddei et al 2008), calculations based on the Geant4 toolkit can successfully reproduce the performance of a TEPC (Far West Technology Inc., model LET-1/2) irradiated by 4 He, 12 C, 16 O, 28 Si and 56 Fe nuclei.…”

“…If one assumes that particles representing a homogeneous radiation field traverse a spherical detector randomly at various impact parameters, then l = 2/3d. There were several experimental (Guetersloh et al 2004, Taddei et al 2006) and theoretical (Nikjoo et al 2002, Taddei et al 2008) studies of TEPC responses to heavyions. In these measurements and calculations the dependence of ǫ on the impact parameter of the ion track was investigated in detail.…”

Analytical expressions for water-to-air stopping-power ratios relevant for accurate dosimetry in particle therapy

“…This would allow for studies of the microscopic energy distribution in the target medium. Tracking of delta electrons has for example been performed with Geant4 (Taddei et al 2008) and a study comparing to this work might be of interest.…”