A COMPARISON OF 2 METHODS FOR ESTIMATING EFFECTIVE DOSE IN ABDOMINAL RADIOLOGY

The quantity effective dose has been estimated using two different tec hniques for radiological examinations of the abdomen. Initially, effec tive dose was calculated from measurements of entrance surface dose ma de with thermoluminescence dosemeters (TLD) used in conjunction with n ormalised organ dose factors. The circular field sizes set ranged from 14 cm to 40 cm in diameter when measured at the image intensifier inp ut plane, whilst the standard film-screen technique used 35 cm x 35 cm film. Both anteroposterior and postero-anterior projections were stud ied at a nominal tube potential of 81 kV. The normalised organ dose da ta were measured using TLD and a Rando anthropomorphic phantom as a fu nction of field size and projection. In the second method measurements of dose.area product were used in conjunction with previously publish ed factors to establish effective dose. For the method involving entra nce surface doses and normalised organ dose factors, effective doses f or 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 th is technique were, on average, 40% lower than those derived using the normalised organ dose data, however both techniques agreed to within 1 0% for the postero-anterior view.