The linear nonthreshold (LNT) model is an assumption made for radiation protection purposes, which has not been (and likely cannot be) scientifically validated in the low dose range. As such, consistency of each epidemiological dataset with the LNT assumption, but not the LNT model itself, can be tested statistically (e.g., linear relationship between dose and risk, no indication of nonlinearlity, estimate of threshold compatible with zero dose), using e.g., Epicure ( https://www.risksciences.com/project/epicure/ ) and R ( https://www.r-project.org ). However, when a dose and dose rate effectiveness factor (DDREF) of >1 applies, the LNT model implies that low dose or low dose-rate exposures may be linear with a shallower slope than for high, acute exposure (rather than that the effect is proportional to dose with a single straight line from high, acute, doses to low doses, low dose rates).

The US National Council on Radiation Protection and Measurements (NCRP) has just published Commentary No. 27 “Implications of recent epidemiologic studies for the linear nonthreshold model and radiation protection”.

Commentary No. 27 prepared by Scientific Committee 1–25 updates NCRP Report No. 136 “Evaluation of the linear-nonthreshold dose-response model for ionizing radiation” published in 2001. Commentary No. 27 provides a comprehensive review of recent relevant epidemiologic studies with quantitative dose-response analyses, and concludes that based on current epidemiologic data, the LNT model should continue to be used for radiation protection purposes.

https://www.ncrppublications.org/Commentaries/27

Many thanks, Ms. Jasna Davidovic.

The linear quadratic (LQ) dose response with an upward curvature following acute exposure is supportive of the need of LDEF (low dose effectiveness factor, i.e., the ratio of the slope of the linear extrapolation from the high dose part of the curve to the slope of the low-dose linear component of the LQ curve). Such LQ dose response for solid cancer is observed, e.g., in male atomic bomb survivors in the following paper.

https://www.researchgate.net/publication/315473633_Solid_Cancer_Incidence_among_the_Life_Span_Study_of_Atomic_Bomb_Survivors_1958-2009

The dose response curve for solid cancer broadly follows a linear model, to which DDREF has therefore been applied. However, the shape of the dose response curve differs among the types of solid cancer, e.g., a linear dose response for breast cancer and thyroid cancer, and a possible threshold for non-melanoma skin cancer (basal cell carcinoma). There is no clear evidence for an association between radiation exposure and some types of cancer such as non-melanoma skin cancer (squamous cell carcinoma), melanoma skin cancer, testicular cancer, renal cell cancer, and other cancers in uterus, pancreas, prostate, and rectum.

The dose response curve for leukemia broadly follows an LQ model, to which DDREF has not therefore been applied. However, the shape of the dose response curve differs among the types of leukemia, e.g., upward curvature for acute myeloid leukemia, and a linear dose response for acute lymphoid leukemia and chronic myeloid leukemia. It has generally been accepted that chronic lymphoid leukemia, but there is mounting evidence for an association between radiation exposure and chronic lymphoid leukemia.

Article Genomic characterization of chronic lymphocytic leukemia (CL...

The following two summary articles for NCRP Commentary No. 27 “Implications of recent epidemiologic studies for the linear nonthreshold model and radiation protection” have been published

[In English]

https://www.researchgate.net/publication/326387649_Implications_of_recent_epidemiologic_studies_for_the_linear_nonthreshold_model_and_radiation_protection

[In Japanese (with the abstract and a table both in English)]

https://www.researchgate.net/publication/325036776_Outline_of_NCRP_Commentary_No_27_Implications_of_recent_epidemiologic_studies_for_the_linear_nonthreshold_model_and_radiation_protection