Use of the Linear No-threshold (LNT) Model in Radiological Protection: An Update

The linear no-threshold (LNT) model was introduced into the radiological protection system by the International Commission on Radiological Protection (ICRP) in 1966. The appropriateness of this model is still hotly debated today. Based on a recently published article, we summarize recent results in radiobiology and epidemiology and discuss their impact on the use of the LNT model regarding radiological protection. The scientific results published in radiobiology and epidemiology have strengthened our scientific knowledge of cancer risks associated with low dose and/or low dose-rate radiation exposure. In radiobiology, early stages of mutational carcinogenesis are considered to play a key role in carcinogenesis, with linear responses at doses as low as 10 mGy. Today, some non-mutation mechanisms appear clearly as non-linear, but their impact on the overall carcinogenesis process remains difficult to assess. In epidemiology, excess cancer risk has been observed at dose levels of 100 mGy or less. Some findings suggest that for some cancers, non-linear dose relationships may exist, but overall, the LNT model does not seem to seriously overestimate the risks of cancer at low doses. Overall, current results in radiobiology or epidemiology do not demonstrate the existence of a dose threshold below which the risk of radiation-induced cancer would be zero. Uncertainties remain, but if such a dose threshold existed for all solid cancers, it could not be greater than a few tens of mGy. In conclusion, we consider that the recent scientific knowledge does not call into question the use of the LNT model to assess cancer risks associated with exposure to ionizing radiation for the purpose of radiological protection. Today, the use of this model seems reasonable, and no other dose-response model seems to be more appropriate or justified for radiological protection purposes.