Comparing stochastic proton interactions simulated using TOPAS-nBio to experimental data from fluorescent nuclear track detectors

Abstract

Whilst Monte Carlo (MC) simulations of proton energy deposition have been well-validated at the macroscopic level, their microscopic validation remains lacking. Equally, no gold-standard yet exists for experimental metrology of individual proton tracks. In this work we compare the distributions of stochastic proton interactions simulated using the TOPAS-nBio MC platform against confocal microscope data for AlO:C,Mg fluorescent nuclear track detectors (FNTDs). We irradiated [Formula: see text] mm FNTD chips inside a water phantom, positioned at seven positions along a pristine proton Bragg peak with a range in water of 12 cm. MC simulations were implemented in two stages: (1) using TOPAS to model the beam properties within a water phantom and (2) using TOPAS-nBio with Geant4-DNA physics to score particle interactions through a water surrogate of AlO:C,Mg. The measured median track integrated brightness (IB) was observed to be strongly correlated to both (i) voxelized track-averaged linear energy transfer (LET) and (ii) frequency mean microdosimetric lineal energy, [Formula: see text], both simulated in pure water. Histograms of FNTD track IB were compared against TOPAS-nBio histograms of the number of terminal electrons per proton, scored in water with mass-density scaled to mimic AlO:C,Mg. Trends between exposure depths observed in TOPAS-nBio simulations were experimentally replicated in the study of FNTD track IB. Our results represent an important first step towards the experimental validation of MC simulations on the sub-cellular scale and suggest that FNTDs can enable experimental study of the microdosimetric properties of individual proton tracks.

Directional Detection of Dark Matter Using Solid-State Quantum Sensing

“…This NV center creation mechanism can be utilized as an alternative approach to localize a neutrino or WIMP-induced damage track [23]: a scattering event induces lattice vacancies along with interstitial nuclei; subsequently, high-temperature treatment of the sample helps develop NV centers preferentially at the damage track, which can then be detected through fluorescence microscopy. Fluorescent nuclear track detection using Al 2 O 3 : C, Mg crystals [156] is a mature field with applications in oncology/dosimetry [157,158], as well as nuclear [159], neutron [160], and beam [161] physics. Such fluorescent nuclear track detectors (FNTDs) capture particle tracks in three dimensions through the electronic activation of color centers in the crystal lattice caused by the local electron cascades triggered by particle interactions [162].…”

TOPAS-nBio: An Extension to the TOPAS Simulation Toolkit for Cellular and Sub-cellular Radiobiology

“…Stochastic proton interactions in fluorescent nuclear track detectors. In an effort to validate the simulated track structure, we compared the simulations to experiments performed with fluorescent nuclear track detectors (FNTDs) at the MGH proton beamline (77). Multiple measurements were taken at 2-4 mm intervals along pristine and spreadout Bragg peaks; however, due to limited microscope time, only a few data points were evaluated.…”

“…9.Validation studies for TOPAS-nBio. Panel A: Comparison of TOPAS-nBio track-structure simulations to measurements using FNTD detectors as described elsewhere(77). Shown are correlations of the width of skewed Gaussian fits to the simulated number of electrons stopping within a 207-nm radius of primary proton tracks and experimentally derived integrated brightness of FNTD tracks within a radius of 207 nm.Panel B: Comparison of the frequency of energy depositions in nucleosome-sized cylinders between different codes, TOPAS-nBio, MOCA8, OREC and CPA100 used by Charlton et al (78, 79).…”

Directional detection of dark matter with diamond

“…Nuclear recoils induce local electron cascades, transforming the color centers via electron capture to F + 2 (2Mg) centers, which exhibit a distinct absorption and emission spectrum. Confocal microscopy combined with reconstructive algorithms yield 3D reconstruction of the nuclear trajectory [64], which has been applied to radiation oncology/dosimetry [65,66], as well as nuclear [67], neutron [68], and beam [69] physics.…”