The debate on the use of linear no threshold for assessing the effects of low doses

Abstract

From December 2004 to July 2005, three reports on the effects of low doses of ionising radiation were released: ICRP (2004), the joint report of the French Academies of Science and Medicine (Tubiana et al 2005), and a report from the American Academy of Sciences (BEIR VII 2005). These reports quote the same recent articles on the biological effects of low doses, yet their conclusions diverge. The French report concludes that recent biological data show that the efficacy of defense mechanisms is modulated by dose and dose rate and that linear no threshold (LNT) is no longer plausible. The ICRP and the BEIR VII reports recognise that there are biologic arguments against LNT but feel that there are not sufficient biological proofs against it to change risk assessment methodology and subsequent regulatory policy based on LNT. They point out the remaining uncertainties and the lack of mechanistic explanations of phenomena such as low dose hyperlethality or the adaptive response. In this context, a critical analysis of the available data is necessary. The epidemiological data and the experimental data challenge the validity of the LNT hypothesis for assessing the carcinogenic effect of low doses, but do not allow its exclusion. Therefore, the main criteria for selecting the most reliable dose-effect relationship from a scientific point of view should be based on biological data. Their analysis should help one to understand the current controversy.

Balancing Radiation Dose and Image Quality: Clinical Applications of Neck Volume CT

“…[6][7][8][9][10][11] In August 2001, the Society of Pediatric Radiology organized a multidisciplinary ALARA conference in that the consensus was a statistically significant, albeit small, individual risk for excess cancer in children from ionizing doses of radiation used in helical CT. On the basis of new and more extensive data, the Committee on the Biologic Effects of Ionizing Radiation VII supported a "linear-no-threshold" model, which states that the risk for cancer in humans proceeds in a linear fashion at lower doses without a "safe" threshold, and that even the smallest dose has the potential to cause a small increase in risk to humans. 13 Although reduction in radiation dose is an important exercise, maintaining high quality of a diagnostic imaging study is also essential to provide an accurate and definitive diagnosis. We must keep a fine balance between image quality and radiation dose.…”

A Review: Development of a Microdose Model for Analysis of Adaptive Response and Bystander Dose Response Behavior

“…A considerable controversy is brewing with respect to the validity of the Linear No-Threshold hypothesis for low doses and low dose rates of ioniz- (Tubiana et al 2005(Tubiana et al , 2006. Morgan (2006) recently discussed the ramifications of the issues as applied to the low level bystanders effect and adaptive response.…”

Comparison of Image Quality and Radiation Dose between Fixed Tube Current and Combined Automatic Tube Current Modulation in Craniocervical CT Angiography

“…Induction of cancer is a stochastic event; however, the risk for cancer in humans proceeds in a linear fashion at lower doses without a "safe" threshold, and even the smallest dose has the potential to cause a small increase in risk to humans. 7,8 A recent survey showed that CT now accounts for about 11% of all radiology procedures in the United States and constitutes approximately two thirds of the collective medical radiation dose. 9 In standard CT of the head and neck, direct radiation effects relative to the eye lenses and the thyroid gland have been documented, likely resulting in cataract formation and the development of thyroid malignancies, respectively.…”