AN INVESTIGATION OF X-RAY-EQUIPMENT FACTORS INFLUENCING PATIENT DOSE IN RADIOGRAPHY

Dose audit is a quality control tool for assessing whether patient dos es are kept as low as reasonably practicable. Limitations of audit for radiographic patients are the inherent imprecision in assessment and the lack of information provided for the identification of high levels of dose. In this report, four equipment parameters are identified as influencing entrance surface dose (ESD). They are film speed, radiatio n quality represented by the X-ray transmission through a 20 mm alumin ium filter, attenuation of the table top and grid, and a geometric fac tor to account for inverse square law attenuation. They have been comb ined into a system speed index (SSI). This was measured for 17 X-ray i nstallations. To test the influence of SSI on dose, ESD was measured u sing a phantom to simulate the attenuation for an anteroposterior view of the lumbar spine. A radiographic dose index (RDI) was defined as t he ESD required to produce a reference optical density of 1.2 at 80 kV . For the measurements it was found that RDI was equal to 16.1/SSI (r = 0.960). The report recommends the use of SSI as an index of dose eff iciency which can be used to interpret the results of patient dose aud its and determine priorities for dose saving strategies.