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Point and Counterpoint |

Rebuttal From Dr DossRebuttal From Dr Doss 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):878-879. doi:10.1378/chest.14-3023
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I welcome the opportunity to respond to Dr McCunney.1 His statement in the opening paragraph of his Point editorial that the adverse health effects from ionizing radiation are cumulative does not take into consideration the important effect of the body’s defensive response to low-dose radiation (LDR) exposure. This response, known as adaptive protection, would reduce the endogenous damage that would have occurred in the absence of the LDR exposure, thereby resulting in less overall DNA damage and cancer.2 For example, in a study of 5,000 childhood cancer survivors who had undergone radiation therapy and were followed up for an average of 29 years, the number of second cancers per kg of tissue in the regions of body subjected to radiation dose of about 20 cGy was found to be less than that in the nonirradiated regions of body.3 This observation and additionally cited examples4 involving a variety of LDR exposures demonstrate the effectiveness of LDR given over an extended period of time in reducing the risk of cancers. Thus, his concern about the number of screening CT scans that may be done in the few decades of follow-up of smokers would not be justified.

The carcinogenic concerns regarding LDR in some of the references cited by Dr McCunney were based on the linear no-threshold hypothesis. However, the hypothesis cannot be considered valid, since the atomic bomb survivor data, recognized generally as the most important data for evaluating LDR cancer risks, do not support the hypothesis5 following the recent update.6 Also, there is considerable amount of additional evidence against the linear no-threshold hypothesis.4

Another reason given for LDR cancer concerns in the references quoted by Dr McCunney is the reported excess solid-cancer mortality rate in the low-dose cohorts of the atomic bomb survivors. The process of extracting excess cancer risk from the survivor data uses the linear dose-response model as an integral part of the analysis.6 The assumed linear model, however, does not fit the data, because of the significant curvature in the dose-response in the 0 to 2 Gy range,6 and so should result in the rejection of the linear dose-response model and the LDR cancer-risk estimates based on it. On the other hand, this shape of dose-response has been shown to be consistent with the radiation hormesis model,5 implying the low-dose cohorts would have reduced cancer risk.

Dr McCunney referred to the reported synergistic effect of cigarette smoking and radiation exposure for lung cancers. However, this relates to high radiation doses. With LDR exposure, lung cancers would be reduced among smokers because of the adaptive protection, as has been observed in human studies.7

In conclusion, there is no evidence for increased risk of cancer from the radiation dose corresponding to multiple CT scans given over an extended period of time. In fact, there is considerable evidence that such a radiation dose enhances the body’s protection resulting in reduced cancers. Hence, the radiation dose from CT scans should not be of concern and should not be considered in making decisions on patient care.

Acknowledgments

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

McCunney RJ. Point: should radiation dose from CT scans be a factor in patient care? Yes. Chest. 2015;147(4):872-874.
 
Feinendegen LE, Pollycove M, Neumann RD. Hormesis by low dose radiation effects: low-dose cancer risk modeling must recognize up-regulation of protection.. In:Baum RP., ed. Therapeutic Nuclear Medicine. Berlin, Germany: Springer; 2013.
 
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]
 
Doss M. Counterpoint: should radiation dose from CT scans be a factor in patient care? No. Chest. 2015;147(4):874-877.
 
Doss M. Linear no-threshold model vs. radiation hormesis. Dose Response. 2013;11(4):480-497. [CrossRef] [PubMed]
 
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]
 
Sanders CL, Scott BR. Smoking and hormesis as confounding factors in radiation pulmonary carcinogenesis. Dose Response. 2008;6(1):53-79. [CrossRef]
 

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References

McCunney RJ. Point: should radiation dose from CT scans be a factor in patient care? Yes. Chest. 2015;147(4):872-874.
 
Feinendegen LE, Pollycove M, Neumann RD. Hormesis by low dose radiation effects: low-dose cancer risk modeling must recognize up-regulation of protection.. In:Baum RP., ed. Therapeutic Nuclear Medicine. Berlin, Germany: Springer; 2013.
 
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]
 
Doss M. Counterpoint: should radiation dose from CT scans be a factor in patient care? No. Chest. 2015;147(4):874-877.
 
Doss M. Linear no-threshold model vs. radiation hormesis. Dose Response. 2013;11(4):480-497. [CrossRef] [PubMed]
 
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]
 
Sanders CL, Scott BR. Smoking and hormesis as confounding factors in radiation pulmonary carcinogenesis. Dose Response. 2008;6(1):53-79. [CrossRef]
 
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