Dose estimate for cone beam CT equipment protocols using Monte Carlo simulation in computational adult anthropomorphic phantoms

Abstract

Cone beam computed tomography (CBCT) has become essential for dental diagnosis in the last decade. The objective of this study was to estimate the effective dose and the absorbed dose in tissue and organ for CBCT protocols intended for dental use. Monte Carlo (MC) simulations were used to estimate the effective dose and absorbed dose in tissue / organ suggested by the International Commission of Radiological Protection (ICPR) in its report ICRP-103. Seven different fields of view (FOV) were simulated. Two CBCT equipment were used in this work: i-Cat Classic CBCT and ProMax 3D CBCT. The code used was MCNPX. Anthropomorphic phantoms FASH (Female Adult MeSH) and MASH (Male Adult MeSH) were used. The results were compared with measurements previously obtained, and they were satisfactory. The tissue and organ doses vary for different FOV. The effective dose was in the range 66-111 μSv for the i-Cat Classic CBCT equipment and 68 - 236 μSv for the ProMax 3D equipment. The ProMax 3D equipment presented absorbed doses of at least 34% higher than the i-Cat Classic equipment in all protocols with the same clinical objective image. For both devices, the largest single contribution to the effective dose was from the salivary glands (31%, between 27 – 36 %) and other tissues (36%, between 31 – 39 %). The highest dose range, using the protocols, was shown in the salivary glands and thyroid. For the i-Cat equipment, the conversion factor dose–area product (DAP) was more efficient. For the ProMax 3D equipment the conversion factor kerma was more effective. The effective dose and the dose absorbed in tissues / organs vary according to the FOV exposure parameters and the positioning of the beam relative to the radiosensitive organs. The conversion factors for the equipment used were satisfactory.