Dosimetry in small-animal CT using Monte Carlo simulations

Abstract

Small-animal computed tomography (micro-CT) imaging devices are increasingly being used in biological research. While investigators are mainly interested in high-contrast, low-noise, and high-resolution anatomical images, relatively large radiation doses are required, and there is also growing concern over the radiological risk from preclinical experiments.This study was conducted to determine the radiation dose in a mouse model for dosimetric estimates using the GEANT4 application for tomographic emission simulations (GATE) and to extend its techniques to various small-animal CT applications. Radiation dose simulations were performed with the same parameters as those for the measured micro-CT data, using the MOBY phantom, a pencil ion chamber and an electrometer with a CT detector.For physical validation of radiation dose, absorbed dose of brain and liver in mouse were evaluated to compare simulated results with physically measured data using thermoluminescent dosimeters (TLDs). The mean difference between simulated and measured data was less than 2.9% at 50 kVp X-ray source.The absorbed doses of 37 brain tissues and major organs of the mouse were evaluated according to kVp changes. The absorbed dose over all of the measurements in the brain (37 types of tissues) consistently increased and ranged from 42.4 to 104.0 mGy. Among the brain tissues, the absorbed dose of the hypothalamus (157.8-414.30 mGy) was the highest for the beams at 50-80 kVp, and that of the corpus callosum (11.2-26.6 mGy) was the lowest. These results can be used as a dosimetric database to control mouse doses and preclinical targeted radiotherapy experiments. In addition, to accurately calculate the mouse-absorbed dose, the X-ray spectrum, detector alignment, and uncertainty in the elemental composition of the simulated materials must be accurately modeled. K: Models and simulations; Dosimetry concepts and apparatus; Microdosimetry and nanodosimetry 1Corresponding author.

A review of small animal dosimetry techniques: image-guided and spatially fractionated therapy

“…Recently, a number of studies have replicated the physical geometry and material composition of mice by creating custom realistic heterogeneous and anthropomorphic mouse phantoms (Figure 2) [72,[131][132][133][134][135][136][137][138]. These phantoms are useful in better replicating the actual radiation scattering events, geometry, and tissue attenuation of actual mice for treatment dose verification.…”

Absorbed dose calculation for a realistic CT-derived mouse phantom irradiated with a standard Cs-137 cell irradiator using a Monte Carlo method

“…The methods utilized to create the geometry of computational models in anthropomorphic phantoms have progressed from portraying structures using quadratic equations to producing voxel-based representations [15][16][17][18][19]. Similarly, the advancement in creating computational models of small animals has developed from the mathematical equation based phantom models [16,20] to subsequently advanced voxel-based models [21][22][23].…”