CT Users Group

TS Istad¹, EG Friberg¹, B Toft^2,3, J Turner^1,4, A Liland¹, W Ali⁵, K Kjærheim⁵, HM Olerud^1,6

¹Norwegian Radiation Protection Authority, Østerås, Norway.
²Gjøvik University College, Norway.
³Norwegian University of Life Science, Norway.
⁴Centre for Health Informatics, City University London, UK.
⁵Cancer Registry of Norway, Oslo.
⁶University of Oslo, Norway

Abstract

Introduction: The "Epidemiological study to quantify risks for paediatric computerized tomography and to optimise doses" (EPI-CT) was set-up by the International Agency for Research on Cancer (IARC) to investigate the relationship between the exposure to ionizing radiation from CT scans in childhood and adolescence and possibly attributable late health effects. We will discuss the work being performed in Norway by the Norwegian Radiation Protection Authority (NRPA) and the Norwegian Cancer Registry (NCR), working in partnership. The NCR has responsibility for the epidemiological methods, establishment of cohort, data collection from RIS, and data analysis and interpretation. The NRPA has responsibility for data collection from PACS, calculation of radiation doses, data analysis and interpretation, optimisation of paediatric CT and dissemination of results.

We will particularly focus on data collection, calculation of radiation doses and optimisation.

Data Collection and Dose Calculation: PACS and RIS systems are well established at all hospitals in Norway and contain information on radiological examinations performed over the last 10 years (PACS) and 20 years or more (RIS). Information stored in these systems allows us to calculate an estimate of the radiation doses delivered for each examination. For this we are using the newly developed PerMos software (Research Centre Henry Tudor, Luxembourg). PerMos performs automatic harvesting of dosimetric data from the DICOM header by querying PACS records, and uses the new NCI-CT software (National Cancer Institute, USA) for calculation of organ doses based on paediatric phantoms of different ages and sizes. For older records that do not exist on PACS, an estimate of radiation dose will be made from RIS records and knowledge about CT-scanners and protocols used in the pre-PACS period. A survey for older scanners and scan protocols is being performed as part of the EPI-CT project.

Epidemiological Study: Radiation doses for patients who were 20 years old or less at the time of their CT examination will be collected. This information will be matched with records from the Norwegian Cancer Registry for statistical analysis. The Norwegian cohort currently consists of more than 30 000 children, and we expect to include more.

Optimisation: As part of the EPI-CT study, we aim to perform optimisation of paediatric CT examinations. For this work, we plan to manufacture and test a paediatric version of the new ICRU dosimetry phantom (John M. Boone, ICRU committee on CT Image Quality and Patient Dosimetry) and scan this with current paediatric CT protocols for the range of current CT scanner models. Software will be developed to automatically evaluate image quality and dose. This part of the work is a collaboration between the partners in Norway and Luxembourg.

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