Radiation exposure from imaging tests: is there an increased cancer risk?

Abstract

The increasing exposure to low-dose radiation from diagnostic testing has prompted renewed interest in evaluating its carcinogenic risk, but quantifying health risk from low-dose radiation exposure remains controversial. The current approach is to adopt the linear non-threshold model, which is commonly applied to high-dose exposure, and apply it to assess risk from low-dose exposure. However, existing data are conflicting and limited to epidemiological studies and/or in vitro analyses. In this article, we will discuss the potential cancer risk from low- and high-dose radiation, their effects on DNA repair response pathways, and the best course of action for patients and providers to minimize risk.

Figure 1. The four models of estimating increased cancer risk from radiation exposure

In the LNT model, risk is proportional to the dose, so even the smallest dose induces cancer. In the threshold model, a certain threshold needs to be reached before the risk of cancer increases. In the hypersensitivity model, risk at lower doses is even higher than predicted by the LNT model, because at low doses (<100 mSv) DNA repair systems are not triggered. In the hormesis model, risk at low doses (<100 mSv) is less than predicted by the LNT model because chronic exposure to low-dose radiation stimulates DNA repair mechanisms. LNT: Linear non-threshold; mSv: Millisieverts. Adapted with permission from the Canadian Nuclear Safety Commission.