CT diagram

Ionizing radiation source and detectors in computed tomography

Computed Tomography Radiation Dose

The way radiation dose is measured in medical imaging varies by modality (type of imaging). For computed tomography (CT), also known as computer aided tomography (CAT), examinations or “CAT scans” use ionizing radiation that is typically measured by the energy output of the equipment and the units of measure are the Gray. For typical CT scans the dose is measured in milligray (mGy). This measurement is not intended to be used as a measure of patient dose. To consider the amount of radiation emitted during an examination the Computed Tomography Volumetric Dose Index (CTDIvol), measured in milligray and provided by the scanner before the scan is performed, is multiplied by the length of a scan (scan length); the resulting measure is the Dose Length Product (DLP), which is typically given in milligrays per centimeter or mGy-cm.

The “equivalent dose” is used when measurements include the biological effects of the radiation, the units for these measurements are Sieverts or Sv.

Computed Tomography–An Increasing Source of Radiation Exposure by David Brenner and Eric Hall, describes CT technology, radiation dose measurement and the topic of population-wide medical radiation exposure.

There have been two studies in recent years that demonstrated a link between the number of CT scans in pediatric patients and their risk of developing cancer. These studies and a lot of media attention have increased pressure on governments and institutions to begin monitoring radiation dose. This often include the reporting of radiation dose in the patient record.

Canadian Cancer Society is a resource for patients concerned about the risk of cancer developing from frequent medical imaging.