Organ Doses for Children from Computed Tomographic Examinations

Computed tomography (CT) offers a high diagnostic capability, but the dose to the patients is high compared to conventional radiography. For estimating the related radiation risk, the assessment of the doses to individual organs resulting from CT examinations, especially in paediatrics, is necessary. Therefore, a catalogue of organ doses from CT examinations of children was complied at the GSF. Being applied for special cases rather than for routine examinations, CT is often operated at 'non-standard' situations. For that reason, the doses were calculated for single CT slices of 1 cm width at varying positions throughout the body. The results form a data base from which organ doses for individual paediatric examinations can be derived by suitably combining the calculated values. Two radiation qualities and two exposure geometries were considered as well as the use of asymmetric beams. The organ dose conversion factors are applicable to babies (at the age of about 2 months) and to children between 5 and 7 years but can be used for other ages as well with the appropriate adjustments. For the calculations, the patients were represented by the GSF tomographic anthropomorphic models BABY and CHILD. The radiation transport in the body was simulated using a Monte Carlo method. The doses are presented as conversion factors of mean organ doses per air kerma free in air on the axis of rotation.