Effective radiation dose and eye lens dose in dental cone beam CT: effect of field of view and angle of rotation

Objective: To quantify the effect of field of view (FOV) and angle of rotation on radiation dose in dental cone beam CT (CBCT) and to define a preliminary volume-dose model. Methods: Organ and effective doses were estimated using 148 thermoluminescent dosemeters placed in an anthropomorphic phantom. Dose measurements were undertaken on a 3D Accuitomo 170 dental CBCT unit (J. Morita, Kyoto, Japan) using six FOVs as well as full-rotation (360 degrees) and half-rotation (180 degrees) protocols. Results: For the 360 degrees rotation protocols, effective dose ranged between 54 mu Sv (4 x 4 cm, upper canine) and 303 mu(17 x 12 cm, maxillofacial). An empirical relationship between FOV dimension and effective dose was derived. The use of a 180 degrees rotation resulted in an average dose reduction of 45% compared with a 360 degrees rotation. Eye lens doses ranged between 95 and 6861 mu Gy. Conclusion: Significant dose reduction can be achieved by reducing the FOV size, particularly the FOV height, of CBCT examinations to the actual region of interest. In some cases, a 180 degrees rotation can be preferred, as it has the added value of reducing the scan time. Eye lens doses should be reduced by decreasing the height of the FOV rather than using inferior FOV positioning, as the latter would increase the effective dose considerably. Advances in knowledge: The effect of the FOV and rotation angle on the effective dose in dental CBCT was quantified. The dominant effect of FOV height was demonstrated. A preliminary model has been proposed, which could be used to predict effective dose as a function of FOV size and position.