Reply: Eliminating Use of the Linear No-Threshold Assumption in Medical Imaging

REPLY: Despite their critical nature, we very much appreciate the comments by Dr. Marcus and Drs. Siegel and Sacks on our Invited Perspective (1). We further appreciate the unmistakable passion they bring to the issue of dose–response relationships in the context of low-level radiation. Importantly, our commentary was not intended as either an endorsement or a refutation of the linear no-threshold (LNT) dose–response model or of any alternative model. Rather, our intent was to provide some background on this issue for the readership of The Journal of Nuclear Medicine. The publication by Siegel et al. (2) had already made a compelling case for the fallacy of the LNT model, and it would have been inappropriate, we feel, to simply ignore the large body of scientific literature that supports or at least does not refute the LNT model—even if this model is ultimately discredited. Such an effort inevitably results in the citation of publications that bolster as well as undermine different scientific positions. Our commentary concluded as follows: “…even if one concedes the validity of the LNT model, it cannot be applied reliably to individuals but only to large populations…and application with certitude of population-derived risk factors to individual patients or even defined patient populations is simply not justified.” Although ignored in the letters from Dr. Marcus and Drs. Siegel and Sacks, and despite our presumed agnosticism, the foregoing conclusion amounts to a tangible refutation of the LNT model in a very important context, that of clinical practice.

• © 2017 by the Society of Nuclear Medicine and Molecular Imaging.