A Monte Carlo Tool for Micro-CT Dose Assessment

Abstract

Dose from ionizing radiation is a major concern for small animal imaging (SAI) with micro computed tomography (micro-CT) similar to clinical CT. It is known that many micro-CT examinations are associated with relatively high dose levels due to the increased resolution levels. Dosimetry in micro-CT can be difficult due to the small object volumes. Therefore, dose evaluations based on Monte Carlo (MC) methods appear to be the convenient approach. Dose measurements and MC simulations were performed for a dual-source micro-CT scanner in cylindrical water equivalent phantoms of various diameters (20-40 mm) using tube voltages from 40 to 60 kV (0.5 mm Al filtration) and a total collimation of 40 mm. Dose profiles were obtained from 3D dose distributions and compared with corresponding profiles obtained with thermoluminescent dosimeters (TLD). Additional ionization chamber measurements were performed for comparison purposes. Organ dose values were determined for a mathematically defined mouse phantom and 3D dose distributions were computed for a mouse specimen as well. Depending on the scan protocol CTDI values ranging from 0.85 to 2.84 mGy/mAs were obtained. Organ doses and 3D dose distributions were consistent compared to measurements and simulations in phantoms. MC-based tools represent the method of choice to determine and to optimize the dose levels in micro-CT.