EFFECTIVE DOSES FOR DIFFERENT TECHNIQUES USED FOR PA CHEST RADIOGRAPHY

A survey of X ray units, used for diagnostic chest examinations in the Leiden region, showed considerable variation in exposure conditions a nd techniques (conventional radiography, mobile unit, lung-shaped filt ers). Varying the exposure conditions, including focus-skin distance ( FSD) and beam quality, as employed in PA chest radiography according t o the survey, effective dose (E) was calculated by Monte Carlo simulat ion of radiation transport. Adult male and female patients were simula ted with the mathematical phantoms ADAM and EVA, respectively. For a t ypical exit dose of 4 mu Gy, E ranges from 7 to 17 mu Sv. Thus, proper choice of technique parameters allows a 2.5-fold dose reduction. For similar conditions, E for EVA may differ up to 28% from its value for ADAM. Varying FSD only, differences in E may reach 34%. Lowest doses w ere found for ADAM at medium FSD, for EVA at small FSD. A small vertic al shift (5 cm) in beam position results in a 10% change in E. Best be am quality for radiation protection is offered by large-HVL beams or, for ADAM, small-HVL beams plus lung filters.