TLD measurements and Monte Carlo calculations of head and neck organ and effective doses for cone beam computed tomography using 3D Accuitomo 170

Objectives: In dentistry, the use of cone beam CT has steadily increased over the last few years. The aim of this study was to measure organ doses and to perform dose calculations based on Monte Carlo (MC) simulations to work out a basis for full three-dimensional (3D) dose calculations for any patient examination performed with the machine used in this study. Methods: TLD-100 LiF detectors were placed at 71 measurement positions on the surface and within a RT-Humanoid phantom to cover all relevant radiosensitive organs and tissues. Three examinations with different protocols were performed with the 3D Accuitomo (R) and dose calculations with MC simulations were carried out for the same three protocols using the EGSnrc MC transport code system. Results: Field of views of 140 x 100, 80 x 50 and 40 x 40 mm(2) were selected, the mean organ doses were measured as 5.2, 2.75 and 1.5 mGy and the effective doses were determined as 250, 97 and 48 mu Sv. For the MC simulation of organ doses and the thermoluminescent dosemeter measurements, an overall agreement within +/- 10.1% (two standard deviations) was achieved. The measured dose values for 3D Accuitomo (R) were about a factor 2 lower when compared with conventional CT examinations. Conclusions: Reliable results for the organ doses as well as effective dose values were achieved with thermoluminescent dosemeter measurements in the RT-Humanoid phantom. This study provides the basis for the application of MC simulations for further dose determinations of cone beam CT machines. The MC calculation may therefore be a valuable tool to support the dentists in the evaluation of the trade-off between additional information that may be relevant to the choice of therapy and the additional dose given to the patient.