Radiation doses and risks from paediatric computed tomography

The use of computed tomography (CT) worldwide has increased dramatically since its introduction. In Australia, more than two million CT services are funded by Medicare every year and the rate of imaging is increasing beyond population growth. CT imaging currently accounts for the largest source of ionising radiation exposure to the population from all diagnostic procedures. There is a small, theoretical risk of carcinogenesis attributable to low doses of ionising radiation based on epidemiological evidence at higher doses and dose rates. The doses from CT examinations fall into this low dose range. Recognition of the potential radiation risks combined with the high utilisation of CT imaging has led to greater awareness of population health risks. Furthermore, the exposure risks from radiation are higher for children than for adults due to their increased radiosensitivity and greater prospective life expectancy. There is only limited information on Australian paediatric CT imaging rates, doses and risks. This thesis aims to assess the medical radiation exposure of children in Australia from CT examinations.

An experimental method for paediatric CT organ dosimetry was developed using a physical anthropomorphic phantom representing a child and high sensitivity thermoluminescent dosemeters. Radiation doses for typical paediatric CT clinical protocols performed at the Royal Children’s Hospital (RCH) in Melbourne were quantified. An analysis of indirect dose computation methods was undertaken to identify a robust and reliable method for paediatric CT organ dosimetry feasible for clinical implementation. A practical method for assessing doses and scan parameters from a local dose survey was developed to enable identification of areas for dose optimisation. Local diagnostic reference levels were established based on the dose distributions from RCH patient data across all paediatric age groups. The first comprehensive analysis of CT imaging frequency and trends for the Australian paediatric population was undertaken. Finally, cancer risk projections for incidence and mortality from paediatric CT scanning have been made for the Australian population.