Radiation doses to the lens of the eye during computerised tomography of the orbit; a comparison of four modern computerised tomography units.

A previous study has looked at the estimated radiation dose to the lens of the eye during CT scanning of the orbit, pituitary fossa and brain with a recently installed GE 9800 Quick CT using a phantom simulating the lens of the eye. In this study the same phantom was used to compare the estimated radiation dose delivered to the lens of the eye by three other newly installed CT units of different manufacture. There was significant variation between the doses measured from the four machines when operated with the parameters commonly used in clinical practice. However, in all cases scanning of the phantom using routine techniques delivered a dose to the simulated lens which was much lower than the threshold dose for cataracts. There is, never-the-less, a potential for delivery of much higher doses.