A comparison of two methods for estimating effective dose in abdominal radiology

The quantity effective dose has been estimated using two different techniques for radiological examinations of the abdomen. Initially, effective dose was calculated from measurements of entrance surface dose made with thermoluminescence dosemeters (TLD) used in conjunction with normalised organ dose factors. The circular field sizes set ranged from 14 cm to 40 cm in diameter when measured at the image intensifier input plane, whilst the standard film-screen technique used 35 cm x 35 cm film. Both anteroposterior and postero-anterior projections were studied at a nominal tube potential of 81 kV. The normalised organ dose data were measured using TLD and a Rando anthropomorphic phantom as a function of field size and projection. In the second method measurements of dose area product were used in conjunction with previously published factors to establish effective dose. For the method involving entrance surface doses and normalised organ dose factors, effective doses for male and female cases were deduced. The method involving dose area product, which does not distinguish between male and female patients, was in closer agreement for the male case. It was also found that the effective doses calculated for the anteroposterior projection using this technique were, on average, 40% lower than those derived using the normalised organ dose data, however both techniques agreed to within 10% for the postero-anterior view. (Author)