Cancer Risk From Multiple Imaging Tests—Reply

In Reply: We agree with Dr Mezrich that the precise nature of the relationship between x-ray radiation and cancer risk is incompletely understood and that maintaining patients' radiation exposures “as low as reasonably achievable” is an important principle. The scientific community's understanding of the relationship between radiation dose and cancer risk currently rests, for reasons of sample size and statistical power,¹ primarily on data from nonimaging sources of radiation, and it is impossible to reconcile every study in the radiation epidemiology literature with every other study. Even so, as we have previously discussed,² the major US (National Academies, National Council on Radiation Protection and Measurements) and international (International Commission on Radiological Protection, United Nations Scientific Committee on the Effects of Atomic Radiation) advisory organizations have reviewed this literature and supported the notions that radiation-associated cancer risks are cumulative and that the linear-no-threshold model best fits the available data for purposes of radiation protection.