Patient radiation dose management in dental facilities according to the X-ray focal distance and the image receptor type

Objectives: To determine particular reference values for patient radiation dose management according to the focus-to-skin distance and the image receptor type. Methods: Air-free ionization chambers and solid state detectors built in quality control devices were used to measure X-ray tube output in a sample of 2811 X-ray units. The mean exposure time was estimated by the local person responsible for the quality assurance programme. From this data, mean air kerma values were calculated at the focus-to-skin distance. To obtain the entrance surface air dose, a backscatter factor of 1.2 was used. Results: Third-quartile values were 5.3 mGy for old X-ray sets with around 10 cm focus-to-skin distance (FSD); for 20 cm FSD, the values were 4.1 mGy for D type, 3.4 mGy for E/F film type and 1.2 mGy for digital image receptors; and for 30 cm FSD the values were 2.1 mGy for D type, 1.8 mGy for E/F film type and 0.6 mGy for digital image receptors. Conclusions: Evidence based on third-quartile values different from those expected justifies the need for particular reference values taking into account image system and focal distance, as a way to improve patient radiation dose management.