Reference doses and patient size in paediatric radiology

There is a wide range in patient size from a newborn baby to a 15 year old adolescent. Reference doses for paediatric radiology can sensibly be established only for specific sizes of children. Here five standard sizes have been chosen, representing 0 (newborn), 1, 5, 10 and 15 year old patients. This selection of standard ages has the advantage of matching the paediatric mathematical phantoms which are often used in Monte Carlo organ dose calculations. A method has been developed for calculating factors for normalising doses measured on individual children to those for the nearest standard-sized 'child'. These normalisation factors for entrance surface dose (ESD) and dose-area product (DAP) measurements depend on the thickness of the real child, the thickness of the nearest standard 'child', and an effective linear attenuation coefficient (μ) which is itself a function of the x-ray spectrum, the field size, and whether or not an antiscatter grid is used. Entrance and exit dose measurements were made with phantom material representing soft tissue to establish μ values for abdominal and head examinations, and with phantom material representing lung for chest examinations. These measurements of μ were confirmed and extended to other x-ray spectra and field sizes by Monte Carlo calculations. The normalisation factors are tabulated for ESD measurements for specific radiographic projections through the head and trunk, and for DAP measurements for complete multiprojection examinations in the trunk. The normalisation factors were applied to European survey data for entrance surface dose and dose-area product measurements to derive provisional reference doses for common radiographic projections and for micturating cystourethrography (MCU) examinations - the most frequent fluoroscopic examination on children. (author)