[Dose evaluation of a flat-panel detector system].

We compared the INNOVA2000 (INNOVA), which has a flat panel detector system, and the Advantx LCLP (LCLP), which has a conventional I. I. system, in terms of the dependence of phantom thickness on patient surface dose (surface dose) and receptor entrance dose (entrance dose). We examined the reduction in surface dose and entrance dose by using an additional filter and shortening the patient detector distance (PDD). The surface dose rate for fluoroscopy with INNOVA was 73.8-63.5%, and the reduction rate was high at a phantom thickness of less than 20 cm compared with LCLP, but such a reduction could not be expected at a phantom thickness of more than 30 cm, depending on maximum dose rate. The rate of reduction in surface dose in the case of exposure was considerably low at a phantom thickness of about 20 cm, while the other's (5, 10, 15, 25, 30 cm) reduction rates were about 40%. The length of PDD with INNOVA was shortened by 5 cm compared with LCLP. As a result, we obtained a reduction rate of surface dose of 11-15%, while the entrance dose was 10% lower. The reduction rate achieved with an additional filter was 43-60% in surface dose rate in fluoroscopy, whereas that of surface dose for exposure was about 50% at phantom thicknesses up to 20 cm, but remained just 25% thereafter. The results indicated that the reduction of surface dose with INNOVA could be changed by means of the phantom thickness, and we consider the effect achieved by the addition of a filter to be the main factor.