This letter is in regard to the recent article, “Studies of the Mortality of Atomic Bomb Survivors, Report 14, 1950–2003: An Overview of Cancer and Noncancer Diseases” (Radiat Res 2012; 177:229–43), by Ozasa et al. (). In the article, the cancer mortality data of the atomic bomb survivors was fitted to an excess relative risk (ERR) model using linear and linear-quadratic dose-dependences for the ERR. Their conclusion after a formal dose-threshold analysis was that there was no threshold for excess cancer risk.

We are generally concerned that the functional forms the authors chose for dose dependence were not flexible enough and might have led them to the conclusion of a zero-dose threshold. For example, the linear-quadratic model was very restrictive, and the restrictions may have caused the linear quadratic curve to pass through the ERR = zero point at zero dose in Fig. 4. While there is...

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