Evaluation of the use of a niobium filter for patient dose reduction in chest radiography.

The performance characteristics of a 50 microns niobium filter and a copper filter of equivalent thickness (0.15 mm) were compared for postero-anterior chest X-ray examination. Radiographs of 20 patients obtained using an automatic exposure control device showed no significant differences in image quality and exposure setting between the filters. Radiation dose distributions measured in a Rando phantom revealed a higher reduction in the patient dose with the niobium filter. The reduction in the effective dose equivalent, produced by the addition of the niobium and copper filters to the standard filter of 2.5 mm aluminium, of 17% and 10%, was relatively small compared with the reductions in the entrance surface dose of 31% and 26%. Our study confirms that drastic alterations in the patient dose by the addition of a dose reduction filter to the usual filtration cannot be expected.