Patient-specific dose assessment using CBCT images and Monte Carlo calculations

Today, the use of Cone-Beam Computed Tomography (CBCT) is increasing rapidly in medical diagnosis, therefore evaluation of patient's dose is a very important issue in radiation protection of patients. This study aimed to evaluate the patient-specific dose using CBCT images. Since CBCT images only showed a part of the head and while, the total anatomical specification of the head should be defined for dose assessment, therefore the whole parts of the head were generated using the data of the Extended Cardiac-Torso (XCAT) reference phantoms and pseudo-images were created. Tissue densities were calculated by the voxel values of pseudo-images and were used as the input file of Gate8.2 Monte Carlo (MC) code. Also, the GIANO CBCT unit was simulated and the absorbed dose was calculated by the code. For verification of this method, Rando phantom with embedded thermoluminescence dosimeters (TLD) with different protocols was used. The results of MC calculations and TLD measurements were compared and statistical analysis was performed using IBM SPSS Statistics. The calculated effective dose values determined by CBCT images for three different Temporomandibular joint, Single-Arch, and Both-Arch protocols were found to be 87 +/- 3 mu Sv, 64 +/- 1 mu Sv, and 66 +/- 2 mu Sv, and the results of thermoluminescence dosimetry were 86 +/- 2 mu Sv, 57 +/- 1 mu Sv, and 63 +/- 3 mu Sv, respectively. There were no significant differences (P-Value > 0.05) between the results of MC calculations using CBCT images and the results of TLD dosimeters. In this study, a method for patient-specific dose assessment using CBCT images was introduced. It was shown that the dose of patients with its specification can be evaluated by CBCT images with acceptable accuracy.