The Risk of Cancer from CT Scans and Other Sources of Low-Dose Radiation: A Critical Appraisal of Methodologic Quality
Authors: Carl H Schultz
Mohan Doss
Linda Suk-Ling Murphy
Romeo Fairley
Journal: Prehospital and disaster medicine (2020)
Discipline: CLINICAL MEDICINE
Keywords: CT scans; cancer risks; disasters; methodology; radiation.
Affiliations: Professor Emeritus of Emergency Medicine and Public Health, Department of Emergency Medicine, UCI School of Medicine, Irvine, CaliforniaUSA., Assistant Clinical Professor of Emergency Medicine, Department of Emergency Medicine, University of Texas Health School of Medicine, San Antonio, TexasUSA., Research Librarian for Health Sciences, University of California, Irvine, CaliforniaUSA., Medical Physicist, Professor, Diagnostic Imaging, Fox Chase Cancer Center, Philadelphia, PennsylvaniaUSA.

Abstract:  Introduction: Concern exists that radiation exposure from computerized tomography (CT) will cause thousands of malignancies. Other experts share the same perspective regarding the risk from additional sources of low-dose ionizing radiation, such as the releases from Three Mile Island (1979; Pennsylvania USA) and Fukushima (2011; Okuma, Fukushima Prefecture, Japan) nuclear power plant disasters. If this premise is false, the fear of cancer leading patients and physicians to avoid CT scans and disaster responders to initiate forced evacuations is unfounded. Study objective: This investigation provides a quantitative evaluation of the methodologic quality of studies to determine the evidentiary strength supporting or refuting a causal relationship between low-dose radiation and cancer. It will assess the number of higher quality studies that support or question the role of low-dose radiation in oncogenesis. Methods: This investigation is a systematic, methodologic review of articles published from 1975-2017 examining cancer risk from external low-dose x-ray and gamma radiation, defined as less than 200 millisievert (mSv). Following the PRISMA guidelines, the authors performed a search of the PubMed, Cochrane, Scopus, and Web of Science databases. Methodologies of selected articles were scored using the Newcastle Ottawa Scale (NOS) and a tool identifying 11 lower quality indicators. Manuscript methodologies were ranked as higher quality if they scored no lower than seven out of nine on the NOS and contained no more than two lower quality indicators. Investigators then characterized articles as supporting or not supporting a causal relationship between low-dose radiation and cancer. Results: Investigators identified 4,382 articles for initial review. A total of 62 articles met all inclusion/exclusion criteria and were evaluated in this study. Quantitative evaluation of the manuscripts' methodologic strengths found 25 studies met higher quality criteria while 37 studies met lower quality criteria. Of the 25 studies with higher quality methods, 21 out of 25 did not support cancer induction by low-dose radiation (P = .0003). Conclusions: A clear preponderance of articles with higher quality methods found no increased risk of cancer from low-dose radiation. The evidence suggests that exposure to multiple CT scans and other sources of low-dose radiation with a cumulative dose up to 100 mSv (approximately 10 scans), and possibly as high as 200 mSv (approximately 20 scans), does not increase cancer risk. 

Retracted: No

PubPeer comments:
 Do not see a comment. , 
 The study present a questionable methodology for a Systematic Review: 1) Scale and scores are NOT recommended in general for the evaluation of quality in Systematic review, according to the Cochrane collaboration  The Cochrane recommended tool for assessing risk of bias is neither a scale nor a checklist. It is a domain-based evaluation in which critical assessments are made separately for different domains . That statement in also extensible out of systematic review of randomized controlled trials to systematic review of observational study, also in environmental stream. 2) A part of NOS scale the author selects 11  lower quality indicator , which also are treated as a scale score. There is a general lack of criticism in the paper. For example, the reason of such scoring is not reported (should be instead). A table in the appendix, with the rationale of such scoring would be very helpful, otherwise the score appear to be arbitrary. 3) Methodology for result synthesis lacking. The author seems to used a qualitative synthesis approach (basically they divided the articles in those we support an effect and those who did not), however under the paragraph  data analysis it is very unclear how they judged such support or refuse. That approach is highly questionable and it is not in line of what is recommended by Cochrane regarding methods of qualitative synthesis. 4) Methodology for the evaluation of the strength of the evidence is lacking. 5) Conclusion stated here  This investigation demonstrates that a preponderance of studies using higher quality case control and cohort methodology support the existence of a threshold for cancer induction by radiation up to a dose of 100 mSv, and possibly as high as 200 mSv. These findings suggest that the cancer risk from this radiation dose is minimal and exposure to at least 10 CT scans, and possibly as many as 20, is unlikely to cause cancer Is not in line of any of the results reported and presents logical flaws (for examples it seems that studies classified somehow as  refutes LNT (and even the classification in such category is questionable and highly unclear as I stated above) magically became  studies that supports the existence of a threshold . The study could be much improved by a better characterization of methodology for systematic review which here it seems has been misunderstood and wrongly applied. ,