Background: If computerized tomography (CT) and other sources of low-dose radiation actually increase the risk of cancer, as some previous studies suggest, thousands of patients receiving diagnostic imaging will develop iatrogenic malignancies. If this premise is false, the fear of cancer that may lead patients and physicians to avoid these powerful diagnostic tools is unfounded. This investigation provides a quantitative evaluation, using objective scoring criteria, of the methodologic quality of studies on both sides of the issue to determine the evidentiary strength supporting or refuting a causal relationship between low-dose radiation and cancer.
Methods: Investigators conducted a systematic methodologic review of articles published from 1975 through 2017 examining the risk of cancer from low-dose radiation. Following the PRISMA guidelines, a search of the PubMed, Cochrane, Scopus, and Web of Science databases identified any literature that discussed cancer and low-dose radiation, defined as less than 200 mSv. Manuscript methodologies were ranked as high quality if they scored no lower than 7 out of 9 on the Newcastle Ottawa Scale (NOS) and contained no more than 2 out of 11 lower quality indicators. They were ranked as lower quality if they received a score of 6 or less on the NOS or contained at least 3 lower quality indicators. We then characterized the articles as supporting or refuting a causal relationship between low-dose radiation and cancer, evaluating this difference using the chi-squared test for independence.
Results: We identified 4382 articles for initial review with 237 meeting criteria for detailed evaluation. After independent full text review, 62 articles were identified for inclusion in the study. Quantitative evaluation of the manuscripts’ methodologic strengths using the two scoring tools found 25 studies met high quality criteria. Of the 25 studies with high quality methods, 21 out of 25 did not support a relationship between cancer induction and low-dose radiation exposure up to 100 to 200 mSv (p = .0003).
Conclusion: A clear preponderance of articles with high quality methods found no increased risk of cancer from low-dose radiation. As such, the evidence strongly suggests exposure to multiple CT scans with a cumulative radiation dose up to 100 mSv (10 scans) and possibly as high as 200 mSv (20 scans) does not increase cancer risk.