| Summary: | Computed tomography (CT) is a medical imaging technology used for the screening and diagnosis of medical conditions. It involves taking numerous X-ray images of a body area or organ and these images are reconstituted into computer-generated pictures. Radiation exposure is calculated in millisieverts (mSv) using effective dose (ED). ED is a means of converting localized radiation dose to a dose that would be equivalent to a whole-body exposure in a reference patient. ED is defined as the total body absorbed dose required to achieve an adequate diagnostic image. CT imaging exposes a person to 2 mSv of radiation (for example a head CT) to 30 mSv of radiation (for example a multiphase abdominal CT). In contrast, it is estimated that a person is exposed to 3 mSv of radiation annually from background radiation. The use of CT has increased over the past decade. In 2011-2012, 4.4 million CT exams were performed in Canada, representing an annual increase of 2.7% since 2003. The national rate for CT scans in 2011-2012 was 126 per 1,000 people. Provincial rates ranged from 209 per 1,000 people (New Brunswick) to 88 per 1,000 people (Alberta). It has been suggested that 26% to 44% of CT scans are ordered inappropriately. With an increase in the use of CT scans, radiation exposure is an important public health concern. The current evidence suggests that doses between 5 and 125 mSv may cause a small but statistically significant increase in cancer risk. Furthermore, frequent radiation exposure leads to high cumulative doses of radiation. The Canadian Nuclear Safety Commission recommends radiation dose limit for exposure to licensed sources of radiation of 1 mSv annually for the public, and 50 mSv annually or 100 mSv over five years for workers (for example nuclear power workers and medical personnel who work with sources of ionizing radiation). This report will review the evidence on the risk of cancer associated with CT exposure and recommended threshold of radiation doses
|
|---|