Radiation dose quantities and risk in neonates in a special care baby unit

Radiographs are taken in the neonatal period most commonly to assist in the diagnosis and management of respiratory difficulties. Frequent accurate radiographic assessment is required and a knowledge of the radiation dose is necessary to justify such exposures. A survey of radiation doses to neonates from diagnostic radiography (chest and abdomen) has been carried out in the special care baby unit of the Royal Free Hospital. Entrance surface dose (ESD) was calculated from quality control measurements on the X-ray unit itself. Direct measurement of radiation doses was also performed using highly sensitive thermoluminescent dosemeters (TLDs) (LiF:Mg,Cu,P), calibrated and tested for consistency in sensitivity. ESD, as calculated from exposure parameters, was found to range from 28 microGy to 58 microGy, with a mean ESD per radiograph of 36+/-6 microGy averaged over 95 examinations. ESDs as derived from TLD crystals ranged from 18 microGy to 58 microGy for 30 radiographic examinations. The mean energy imparted, the mean whole body dose per radiograph and the mean effective dose were estimated to be 14+/-8 microJ, 10+/-4 microGy and 8+/-2 microSv, respectively. Assuming that neonates and fetuses are equally susceptible to carcinogenic effects of radiation, which involve an overestimation of risk, the radiation risk of childhood cancer from a single radiograph was estimated to be of the order (0.3-1.3) x 10(-6). Radiation doses compared favourably with the reference values of 80 microGy ESD published by the Commission of the European Communities in 1996, and 50 microGy published by the National Radiological Protection Board in 2000.