Weak defense of the LNT model

 

Since the publication of the 2012 update to the atomic bomb survivor data by Ozasa et al. there has been a very weak defense or no defense of the LNT model by the LNT model supporters. This is indicative of the weakness of the current evidence supporting the LNT model. Some examples are given below.

 

In the debate in Medical Physics in 2014 on the subject "Low-dose radiation is beneficial, not harmful" (Doss, Little, et al.) Dr. Little did not use the atomic bomb survivor data (which are recognized to be the most important data for radiation effects) to justify low-dose radiation carcinogenicity, after having stated in the previous debate in 2009 "Most of the information on radiation-induced cancer risk comes from (a) the Japanese atomic bomb survivors, (b) ...".

 

Thus, the major change in the atomic bomb survivor data, that they do not support the LNT model any longer, is being recognized implicitly by the proponents of the LNT model. The evidence he cited in support of low-dose radiation cancer risk were:

 

  • Oxford survey of childhood cancers and "Risk coefficients for childhood cancer after intrauterine irradiation: a review" by Wakeford and Little, 2003. A more recent review (Brent,2013) indicated that there are cohort studies (which are superior to case-control studies) that do not show an increased risk, and so there is no definitive conclusion on prenatal low-dose irradiation.

  • 2013 Study by Kendall et al. of childhood leukaemia and other cancers in Great Britain as a function of background radiation that showed excess relative risk (RR) /mSv for leukemias of 1.12 (95% CI:1.03-1.22). Since the study did not consider important factors such as breast feeding and childcare attendance which are known to affect childhood leukemia risk, and considering the lower limit of 95% CI is 1.03, small changes in such factors could render the relative risk not significant.  Hence we should await better studies and not use the conclusion from this study. Also, please note that all childhood cancers had RR=1.03, (95% CI: 1.0-1.07), and small changes in all cancer rates coulld make the RR not significant.

  • Pearce et al, 2012 study that claimed increased leukemias and brain cancers following childhood CT scans.  This study has a major problem of reverse causation, as indicated in several criticisms of the article (Boice, 2013), (Walsh, 2014), (Boice, 2015)


There have been several challenges to the LNT model based articles in journals in the form of Letters to the Editor. A couple of examples are given below:

 

Radiation doses from radiological imaging do not increase the risk of cancer - Letter to the editor in response to: What we know and what we don't know about cancer risks associated with radiation doses from radiological imaging by Brenner Brenner's Reply did not respond to any of the issues raised.

 

Radiation dose justification and optimization should not be applied to medical imaging in emergency medicine Letter to the editor in response to: Applications of justification and optimization in medical imaging: examples of clinical guidance for computed tomography use in emergency medicine.   There was no response by the authors to the Letter.

 

As can be seen in the examples above, there have been weak defense of the LNT model.  This is indicative of the weakness of the current evidence supporting the LNT model.

 

Thus, in our view, the controversial issue of low-dose radiation cancer risk is on the verge of being resolved in favor of radiation hormesis.