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Point and Counterpoint |

COUNTERPOINT: Should Radiation Dose From CT Scans Be a Factor in Patient Care? NoRadiation Dose a Factor in Patient Care? No FREE TO VIEW

Mohan Doss, PhD
Author and Funding Information

From the Department of Diagnostic Imaging, Fox Chase Cancer Center.

CORRESPONDENCE TO: Mohan Doss, PhD, Department of Diagnostic Imaging, Fox Chase Cancer Center, 333 Cottman Ave, Philadelphia, PA 19111; e-mail: mohan.doss@fccc.edu


FINANCIAL/NONFINANCIAL DISCLOSURES: The author has reported to CHEST that no potential conflicts of interest exist with any companies/organizations whose products or services may be discussed in this article.

Reproduction of this article is prohibited without written permission from the American College of Chest Physicians. See online for more details.


Chest. 2015;147(4):874-877. doi:10.1378/chest.14-3022
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There is considerable disagreement in the scientific community on the carcinogenicity of low-dose radiation (LDR). Since the 1950s, international advisory bodies have consistently recommended using the linear no-threshold (LNT) model to extrapolate the high-dose cancer risks to low doses as a conservative approach to radiation safety, implying that LDR would increase the cancer risk. Hence, it is generally considered prudent to try to reduce the radiation dose from CT scans to reduce patients’ cancer risk. The entire radiologic community has embarked on efforts to reduce the radiation dose from CT scans. Are these LDR carcinogenic concerns and CT scan dose-reduction efforts justified? The answer to the question depends on (1) whether LDR is indeed carcinogenic, and (2) whether the CT scan dose-reduction efforts are likely to result in improved patient health. These two questions will be examined in some detail now to answer the question “Should radiation dose from CT scans be a factor in patient care?”

The data from atomic bomb survivors have been described as the gold standard for determining the health effects of LDR.1 These data have been used by the influential Biological Effects of Ionizing Radiation (BEIR) VII report2 to discount the possibility of any beneficial effects from LDR, for ruling out the possibility of a threshold dose for increased cancers, and for calculating LDR cancer risk factors using the LNT model. An update to the atomic bomb survivor data was published,3 and analysis of the data has shown that with the increased statistics, the data are no longer compatible with the LNT model but are more consistent with a radiation hormesis model, when a correction is applied for a likely negative bias in the baseline cancer mortality rate (Fig 1),4,5 implying that LDR would reduce, rather than increase, the cancer risk.

Figure Jump LinkFigure 1 –  ERR for all solid-cancer mortality in atomic bomb survivors (data from Ozasa et al3) corrected for −20% bias in baseline cancer mortality rate,4,5 plotted as a function of colon dose. For doses < 0.3 Gy, the black circles show the average of data < 0.3 Gy, and gray circles show the individual data points. Error bars are ± SD. ERR = excess relative risk.Grahic Jump Location

Another dataset that has been used to raise LDR carcinogenic concerns is the 15-country study of radiation workers.2,6,7 Recent corrections to the data in this study have negated its original conclusion that LDR is carcinogenic.8

A third reason stated for concerns regarding LDR is the DNA damage caused by LDR.2,7 Whereas LDR does cause some DNA damage, it also results in increasing the bodily defenses known as adaptive protection, and the increased protection would result in reducing the endogenous damage in the subsequent period, resulting in reduced overall DNA damage and improved health.9 Also, since LDR stimulates the immune system, and since the immune system plays an important role in maintaining occult cancers in check, LDR would tend to reduce the cancers.9 There are also other examples, such as the activities of exercise and learning, that cause increased DNA damage, but these result in improved health due to the adaptive protective response of the body following the activities.10

A fourth reason given for LDR concerns in some publications6,9 are the reports of increased cancers observed following prenatal irradiation or following childhood CT scans. As discussed in recent publications,8,9 such studies have major flaws, making their conclusions not reliable.

Thus, all the main reasons that have been presented in recent publications for the carcinogenic concerns regarding LDR are no longer valid. On the other hand, there is a considerable amount of evidence for the cancer preventive effect of LDR and/or the presence of a threshold dose for the induction of cancer (Fig 1, Table 1). In view of the discussion thus far and evidence, there is no valid reason for the carcinogenic concerns regarding the radiation dose from CT scans.

Table Graphic Jump Location
TABLE 1 ]  Evidence Showing Reduction of Cancers Following Low-Dose Radiation or for a Threshold Dose for Cancer Induction

LDR carcinogenic concerns and the consequential actions to reduce CT scan dose can, indeed, result in harming patients in many different ways, even if the LNT model (which we have seen is not validated by evidence) is used to estimate the benefit of reduced cancers due to the dose reduction.20 Whereas the CT scan dose-reduction efforts have been justified based on the LNT model-based carcinogenic concerns, the lifetime attributable risk of cancer mortality due to CT scans (based on the LNT model) is very small (eg, one in 4,000 in a 10-year-old child).20 On the other hand, the chance of benefitting from the CT scan, when it is indicated, is orders of magnitude greater.20 Thus, balancing the benefit and risk, one should always conclude that the CT scan should be performed, when indicated by clinical conditions.20 However, some parents are known to refuse the CT scans when informed of the cancer risks from them, and even some physicians are known to not order a CT scan based on the dose concerns.20 Thus, the CT dose concerns and the resulting actions may already be harming patients.

One consequence of the CT dose concerns is the effort underway to acquire CT images with lower radiation dose settings. Whereas dose reductions of the order of 25% may not have any significant effect on diagnosis, larger dose reductions may decrease the diagnostic accuracy, as seen in a 18-reader study of CT scans of an anthropomorphic liver phantom containing low-contrast, low-attenuation lesions.21 A retrospective study of pediatric patient CT scans found that some scans acquired at the lowest dose settings were not of diagnostic quality,20 indicating the dose-reduction efforts may already have potentially harmed some patients due to the reduced diagnostic accuracy. Thus, the CT scan dose concerns and the consequential actions taken are potentially harmful to the patients.

LDR carcinogenic concerns have resulted in concerted efforts by the entire radiologic community to reduce the radiation dose from CT scans. The atomic bomb survivor data, which are the primary basis for these concerns, no longer validate these concerns, since the data are more consistent with radiation hormesis than with the LNT model. Also, a considerable amount of evidence supports reduction of cancers from LDR and/or the presence of a threshold dose for cancer induction. Therefore, the dose-reduction efforts may not result in any benefit of reducing cancer risk in patients. On the other hand, the radiation dose concerns and dose-reduction efforts can harm patients, due to worsened image quality and diagnostic accuracy, refusal of patients to undergo recommended scans, and the decision by physicians to not order indicated scans. Hence, the definitive answer to the question “Should radiation dose from CT scans be a factor in patient care?” is “no.”

Other contributions: The views and opinions expressed herein are those of the author and do not necessarily reflect those of his employer.

Hall EJ, Brenner DJ. Cancer risks from diagnostic radiology. Br J Radiol. 2008;81(965):362-378. [CrossRef] [PubMed]
 
National Research Council. Health Risks from Exposure to Low Levels of Ionizing Radiation: BEIR VII Phase 2, National Research Council (US). Committee to Assess Health Risks from Exposure to Low Level of Ionizing Radiation. Washington, DC: National Academies Press; 2006.
 
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(3):229-243. [CrossRef] [PubMed]
 
Doss M. Evidence supporting radiation hormesis in atomic bomb survivor cancer mortality data. Dose Response. 2012;10(4):584-592. [CrossRef] [PubMed]
 
Doss M. Linear no-threshold model vs. radiation hormesis. Dose Response. 2013;11(4):480-497. [CrossRef] [PubMed]
 
Brenner DJ. What we know and what we don’t know about cancer risks associated with radiation doses from radiological imaging. Br J Radiol. 2014;87(1035):20130629. [CrossRef] [PubMed]
 
Brenner DJ, Hall EJ. Computed tomography—an increasing source of radiation exposure. N Engl J Med. 2007;357(22):2277-2284. [CrossRef] [PubMed]
 
Doss M. Radiation doses from radiological imaging do not increase the risk of cancer. Br J Radiol. 2014;87(1036):20140085. [CrossRef] [PubMed]
 
Doss M, Little MP, Orton CG. Point/counterpoint: low-dose radiation is beneficial, not harmful. Med Phys. 2014;41(7):070601. [CrossRef] [PubMed]
 
Doss M. Low dose radiation adaptive protection to control neurodegenerative diseases. Dose Response. 2014;12(2):277-287. [CrossRef] [PubMed]
 
Tubiana M, Diallo I, Chavaudra J, et al. A new method of assessing the dose-carcinogenic effect relationship in patients exposed to ionizing radiation. A concise presentation of preliminary data. Health Phys. 2011;100(3):296-299. [CrossRef] [PubMed]
 
Sakamoto K. Radiobiological basis for cancer therapy by total or half-body irradiation. Nonlinearity Biol Toxicol Med. 2004;2(4):293-316. [CrossRef] [PubMed]
 
Hwang SL, Guo HR, Hsieh WA, et al. Cancer risks in a population with prolonged low dose-rate gamma-radiation exposure in radiocontaminated buildings, 1983-2002. Int J Radiat Biol. 2006;82(12):849-858. [CrossRef] [PubMed]
 
Cuttler JM. Leukemia incidence of 96,000 Hiroshima atomic bomb survivors is compelling evidence that the LNT model is wrong: Edward Calabrese’s papers “Origin of the linear no threshold (LNT) dose-response concept” (Arch Toxicol (2013) 87:1621-1633) and “How the US National Academy of Sciences misled the world community on cancer risk assessment: new findings challenge historical foundations of the linear dose response” (Arch Toxicol (2013) 87:2063-2081). Arch Toxicol. 2014;88(3):847-848. [PubMed]
 
Kostyuchenko VA, Krestinina LY. Long-term irradiation effects in the population evacuated from the east-Urals radioactive trace area. Sci Total Environ. 1994;142(1-2):119-125. [CrossRef] [PubMed]
 
Miller AB, Howe GR, Sherman GJ, et al. Mortality from breast cancer after irradiation during fluoroscopic examinations in patients being treated for tuberculosis. N Engl J Med. 1989;321(19):1285-1289. [CrossRef] [PubMed]
 
Pollycove M. Radiobiological basis of low-dose irradiation in prevention and therapy of cancer. Dose Response. 2007;5(1):26-38. [CrossRef]
 
Denton GRW, Namazi S. Indoor radon levels and lung cancer incidence on Guam. Procedia Environmental Sciences. 2013;18:157-166. [CrossRef]
 
Sanders CL. Radiation Hormesis and the Linear-No-Threshold Assumption. Heidelberg, Germany: Springer; 2010:43-44.
 
Brody AS, Guillerman RP. Don’t let radiation scare trump patient care: 10 ways you can harm your patients by fear of radiation-induced cancer from diagnostic imaging. Thorax. 2014;69(8):782-784. [CrossRef] [PubMed]
 
Goenka AH, Herts BR, Obuchowski NA, et al. Effect of reduced radiation exposure and iterative reconstruction on detection of low-contrast low-attenuation lesions in an anthropomorphic liver phantom: an 18-reader study. Radiology. 2014;272(1):154-163. [CrossRef] [PubMed]
 

Figures

Figure Jump LinkFigure 1 –  ERR for all solid-cancer mortality in atomic bomb survivors (data from Ozasa et al3) corrected for −20% bias in baseline cancer mortality rate,4,5 plotted as a function of colon dose. For doses < 0.3 Gy, the black circles show the average of data < 0.3 Gy, and gray circles show the individual data points. Error bars are ± SD. ERR = excess relative risk.Grahic Jump Location

Tables

Table Graphic Jump Location
TABLE 1 ]  Evidence Showing Reduction of Cancers Following Low-Dose Radiation or for a Threshold Dose for Cancer Induction

References

Hall EJ, Brenner DJ. Cancer risks from diagnostic radiology. Br J Radiol. 2008;81(965):362-378. [CrossRef] [PubMed]
 
National Research Council. Health Risks from Exposure to Low Levels of Ionizing Radiation: BEIR VII Phase 2, National Research Council (US). Committee to Assess Health Risks from Exposure to Low Level of Ionizing Radiation. Washington, DC: National Academies Press; 2006.
 
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(3):229-243. [CrossRef] [PubMed]
 
Doss M. Evidence supporting radiation hormesis in atomic bomb survivor cancer mortality data. Dose Response. 2012;10(4):584-592. [CrossRef] [PubMed]
 
Doss M. Linear no-threshold model vs. radiation hormesis. Dose Response. 2013;11(4):480-497. [CrossRef] [PubMed]
 
Brenner DJ. What we know and what we don’t know about cancer risks associated with radiation doses from radiological imaging. Br J Radiol. 2014;87(1035):20130629. [CrossRef] [PubMed]
 
Brenner DJ, Hall EJ. Computed tomography—an increasing source of radiation exposure. N Engl J Med. 2007;357(22):2277-2284. [CrossRef] [PubMed]
 
Doss M. Radiation doses from radiological imaging do not increase the risk of cancer. Br J Radiol. 2014;87(1036):20140085. [CrossRef] [PubMed]
 
Doss M, Little MP, Orton CG. Point/counterpoint: low-dose radiation is beneficial, not harmful. Med Phys. 2014;41(7):070601. [CrossRef] [PubMed]
 
Doss M. Low dose radiation adaptive protection to control neurodegenerative diseases. Dose Response. 2014;12(2):277-287. [CrossRef] [PubMed]
 
Tubiana M, Diallo I, Chavaudra J, et al. A new method of assessing the dose-carcinogenic effect relationship in patients exposed to ionizing radiation. A concise presentation of preliminary data. Health Phys. 2011;100(3):296-299. [CrossRef] [PubMed]
 
Sakamoto K. Radiobiological basis for cancer therapy by total or half-body irradiation. Nonlinearity Biol Toxicol Med. 2004;2(4):293-316. [CrossRef] [PubMed]
 
Hwang SL, Guo HR, Hsieh WA, et al. Cancer risks in a population with prolonged low dose-rate gamma-radiation exposure in radiocontaminated buildings, 1983-2002. Int J Radiat Biol. 2006;82(12):849-858. [CrossRef] [PubMed]
 
Cuttler JM. Leukemia incidence of 96,000 Hiroshima atomic bomb survivors is compelling evidence that the LNT model is wrong: Edward Calabrese’s papers “Origin of the linear no threshold (LNT) dose-response concept” (Arch Toxicol (2013) 87:1621-1633) and “How the US National Academy of Sciences misled the world community on cancer risk assessment: new findings challenge historical foundations of the linear dose response” (Arch Toxicol (2013) 87:2063-2081). Arch Toxicol. 2014;88(3):847-848. [PubMed]
 
Kostyuchenko VA, Krestinina LY. Long-term irradiation effects in the population evacuated from the east-Urals radioactive trace area. Sci Total Environ. 1994;142(1-2):119-125. [CrossRef] [PubMed]
 
Miller AB, Howe GR, Sherman GJ, et al. Mortality from breast cancer after irradiation during fluoroscopic examinations in patients being treated for tuberculosis. N Engl J Med. 1989;321(19):1285-1289. [CrossRef] [PubMed]
 
Pollycove M. Radiobiological basis of low-dose irradiation in prevention and therapy of cancer. Dose Response. 2007;5(1):26-38. [CrossRef]
 
Denton GRW, Namazi S. Indoor radon levels and lung cancer incidence on Guam. Procedia Environmental Sciences. 2013;18:157-166. [CrossRef]
 
Sanders CL. Radiation Hormesis and the Linear-No-Threshold Assumption. Heidelberg, Germany: Springer; 2010:43-44.
 
Brody AS, Guillerman RP. Don’t let radiation scare trump patient care: 10 ways you can harm your patients by fear of radiation-induced cancer from diagnostic imaging. Thorax. 2014;69(8):782-784. [CrossRef] [PubMed]
 
Goenka AH, Herts BR, Obuchowski NA, et al. Effect of reduced radiation exposure and iterative reconstruction on detection of low-contrast low-attenuation lesions in an anthropomorphic liver phantom: an 18-reader study. Radiology. 2014;272(1):154-163. [CrossRef] [PubMed]
 
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