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Letters No Increased Risk of Cancer From CT This letter is with reference to the recent article by Albert [1], “Radiation Risk From CT: Implications for Cancer Screening,” in which the author has raised concerns regarding the increased cancer risk to patients from CT. The purpose of this letter is to discuss some of the stated reasons for the concerns and show that such concerns may no longer be justified in view of data and analyses published in the past few years. The author states that the concern regarding the ionizing radiation from CT is because of “the fact that it is a well-established carcinogen, even at relatively low doses,” referencing four publications. The first publication [2], the American College of Radiology white paper on radiation dose, refers to the BEIR VII report that uses a linear-no-threshold (LNT) model for cancer risk from radiation, primarily based on atomic bomb survivor data. The second publication [3] also primarily uses atomic bomb survivor data to establish the cancer risk from low-dose radiation. The third publication [4] is a 15-country study of radiation workers. The fourth publication [5] is a meta-analysis of leukemia risk in studies of low-dose radiation cohorts. Although it has been standard practice (e.g., in the BEIR VII report) to claim that the atomic bomb survivor data are consistent with the LNT model for radiation-induced cancers and therefore low-dose radiation can increase the risk of cancer, the latest update to the atomic bomb survivor data by Ozasa et al. [6] is qualitatively different from earlier such reports because it shows lower than expected cancer rates in the 0.3–0.7 Gy dose region [6]. The resultant curvature in doseresponse relationship is significant (with a p value of 0.02) in this update in comparison with earlier reports, as seen in Table 7 of the study by Ozasa et al., and cannot be explained with the LNT model [6] but is consistent with the radiation hormesis model [7]. Hence, the radiation cancer risk model described in the BEIR VII report, which was based on the observed linear dose-response
relationship in the atomic bomb survivor data (at the time of the report), would need to be revised and would no longer show increased risk of cancer from low-dose radiation. Another dataset that has been used to show the increased cancer risk from low-dose radiation is the 15-country study of radiation workers. This study showed an increased risk of cancer from low-dose radiation mainly because of the reported increased cancers in the Canadian radiation workers. Two years ago, the Canadian Nuclear Safety Commission (CNSC) stated that problems had been found in the Canadian data, and their data no longer show increased risk of cancer for the radiation workers [8]. CNSC has withdrawn the Canadian data from use pending further investigation. With the Canadian data removed, the 15-country study would no longer show an increased cancer risk from low-dose radiation. The fourth publication referred to in the study by Albert [1], the meta-analysis of leukemia risk in low-dose cohorts, includes 23 studies, and most of these studies are consistent with no increased risk of leukemia. The low statistics of these studies would not enable determination of the shape of dose response at low doses. Thus, the concerns raised in the four referenced publications in the study by Albert [1] may not be relevant because they have been superseded by newer data and analyses. Hence, there is no longer any credible reason to support the claims of increased risk of cancer from low-dose radiation. On the other hand, considerable evidence has accumulated since the time of the BEIR VII report for the beneficial effects of low-dose radiation, including reduction of cancers [7]. In view of this, it may be advisable to rethink the current CT dose reduction efforts on the basis of carcinogenic concerns because such efforts may not result in any health benefit to patients. Mohan Doss Fox Chase Cancer Center, Philadelphia, PA
References 1. Albert JM. Radiation risk from CT: implications for cancer screening. AJR 2013; 201:[web]W81– W87 2. Amis ES Jr, Butler PF. Applegate KE, et al. American College of Radiology white paper on radiation dose in medicine. J Am Coll Radiol 2007; 4:272–284 3. Brenner DJ, Doll R, Goodhead DT, et al. Cancer risks attributable to low doses of ionizing radioation: assessing what we really know. Proc Natl Acad Sci USA 2003; 100:13761–13766 4. Cardis E, Vrijheid M, Blettner M, et al. The 15-Country Collaborative Study of Cancer Risk Among Radiation Workers in the Nuclear Industry: estimates of radiation-related cancer risks. Radiat Res 2007; 167:396–416 5. Daniels RD, Schubauer-Berigan MK. A metaanalysis of leukaemia risk from protracted exposure to low-dose gamma radiation. Occup Environ Med 2011; 68:457–464 6. Ozasa K, Shimizu Y, Suyama A, et al. Studies of the mortality of atomic bomb survivors, report 14, 1950–2003: an overview of cancer and noncancer diseases. Radiat Res 2012; 177:229–243 7. Doss M. Linear no-threshold model vs. radiation hormesis. Dose Response 2013; 11:495–512 8. Canadian Nuclear Safety Commission website. Verifying Canadian nuclear energy worker radiation risk: a reanalysis of cancer mortality in Canadian nuclear energy workers (1957–1994)—summary report. nuclearsafety.gc.ca/pubs_catalogue/ uploads/INFO-0811-Verifying-Canadian-Nuclear-Energy-Worker-Radiation-Risk-A-Reanalysisof-Cancer-Mortality-in-Canadian-Nuclear-Energy-Workers-1957-1994_e.pdf. Published June 2011. Accessed November 15, 2012
DOI:10.2214/AJR.13.11525 WEB—This is a web exclusive article.
AJR 2014; 202:W410 0361–803X/14/2024–W410 © American Roentgen Ray Society
W410
AJR:202, April 2014
Letters No Increased Risk of Cancer From CT This letter is with reference to the recent article by Albert [1], “Radiation Risk From CT: Implications for Cancer Screening,” in which the author has raised concerns regarding the increased cancer risk to patients from CT. The purpose of this letter is to discuss some of the stated reasons for the concerns and show that such concerns may no longer be justified in view of data and analyses published in the past few years. The author states that the concern regarding the ionizing radiation from CT is because of “the fact that it is a well-established carcinogen, even at relatively low doses,” referencing four publications. The first publication [2], the American College of Radiology white paper on radiation dose, refers to the BEIR VII report that uses a linear-no-threshold (LNT) model for cancer risk from radiation, primarily based on atomic bomb survivor data. The second publication [3] also primarily uses atomic bomb survivor data to establish the cancer risk from low-dose radiation. The third publication [4] is a 15-country study of radiation workers. The fourth publication [5] is a meta-analysis of leukemia risk in studies of low-dose radiation cohorts. Although it has been standard practice (e.g., in the BEIR VII report) to claim that the atomic bomb survivor data are consistent with the LNT model for radiation-induced cancers and therefore low-dose radiation can increase the risk of cancer, the latest update to the atomic bomb survivor data by Ozasa et al. [6] is qualitatively different from earlier such reports because it shows lower than expected cancer rates in the 0.3–0.7 Gy dose region [6]. The resultant curvature in doseresponse relationship is significant (with a p value of 0.02) in this update in comparison with earlier reports, as seen in Table 7 of the study by Ozasa et al., and cannot be explained with the LNT model [6] but is consistent with the radiation hormesis model [7]. Hence, the radiation cancer risk model described in the BEIR VII report, which was based on the observed linear dose-response
relationship in the atomic bomb survivor data (at the time of the report), would need to be revised and would no longer show increased risk of cancer from low-dose radiation. Another dataset that has been used to show the increased cancer risk from low-dose radiation is the 15-country study of radiation workers. This study showed an increased risk of cancer from low-dose radiation mainly because of the reported increased cancers in the Canadian radiation workers. Two years ago, the Canadian Nuclear Safety Commission (CNSC) stated that problems had been found in the Canadian data, and their data no longer show increased risk of cancer for the radiation workers [8]. CNSC has withdrawn the Canadian data from use pending further investigation. With the Canadian data removed, the 15-country study would no longer show an increased cancer risk from low-dose radiation. The fourth publication referred to in the study by Albert [1], the meta-analysis of leukemia risk in low-dose cohorts, includes 23 studies, and most of these studies are consistent with no increased risk of leukemia. The low statistics of these studies would not enable determination of the shape of dose response at low doses. Thus, the concerns raised in the four referenced publications in the study by Albert [1] may not be relevant because they have been superseded by newer data and analyses. Hence, there is no longer any credible reason to support the claims of increased risk of cancer from low-dose radiation. On the other hand, considerable evidence has accumulated since the time of the BEIR VII report for the beneficial effects of low-dose radiation, including reduction of cancers [7]. In view of this, it may be advisable to rethink the current CT dose reduction efforts on the basis of carcinogenic concerns because such efforts may not result in any health benefit to patients. Mohan Doss Fox Chase Cancer Center, Philadelphia, PA
References 1. Albert JM. Radiation risk from CT: implications for cancer screening. AJR 2013; 201:[web]W81– W87 2. Amis ES Jr, Butler PF. Applegate KE, et al. American College of Radiology white paper on radiation dose in medicine. J Am Coll Radiol 2007; 4:272–284 3. Brenner DJ, Doll R, Goodhead DT, et al. Cancer risks attributable to low doses of ionizing radioation: assessing what we really know. Proc Natl Acad Sci USA 2003; 100:13761–13766 4. Cardis E, Vrijheid M, Blettner M, et al. The 15-Country Collaborative Study of Cancer Risk Among Radiation Workers in the Nuclear Industry: estimates of radiation-related cancer risks. Radiat Res 2007; 167:396–416 5. Daniels RD, Schubauer-Berigan MK. A metaanalysis of leukaemia risk from protracted exposure to low-dose gamma radiation. Occup Environ Med 2011; 68:457–464 6. Ozasa K, Shimizu Y, Suyama A, et al. Studies of the mortality of atomic bomb survivors, report 14, 1950–2003: an overview of cancer and noncancer diseases. Radiat Res 2012; 177:229–243 7. Doss M. Linear no-threshold model vs. radiation hormesis. Dose Response 2013; 11:495–512 8. Canadian Nuclear Safety Commission website. Verifying Canadian nuclear energy worker radiation risk: a reanalysis of cancer mortality in Canadian nuclear energy workers (1957–1994)—summary report. nuclearsafety.gc.ca/pubs_catalogue/ uploads/INFO-0811-Verifying-Canadian-Nuclear-Energy-Worker-Radiation-Risk-A-Reanalysisof-Cancer-Mortality-in-Canadian-Nuclear-Energy-Workers-1957-1994_e.pdf. Published June 2011. Accessed November 15, 2012
DOI:10.2214/AJR.13.11525 WEB—This is a web exclusive article.
AJR 2014; 202:W410 0361–803X/14/2024–W410 © American Roentgen Ray Society
W410
AJR:202, April 2014
