THE LNT-CONTROVERSY AND THE CONCEPT OF “CONTROLLABLE DOSE”

Abstract

There is no firm scientific information on the potential health effects, such as increased cancer rates, due to low doses of ionizing radiation. In view of this uncertainty ICRP has adopted as a prudent default option the linear no-threshold (LNT) assumption and has used it to derive nominal risk coefficients. Subsequent steps, such as the comparison of putative fatality rates in radiation workers with observed accident rates in other professions, have given the risk estimates a false appearance of scientific fact. This has encouraged meaningless computations of radiation-induced fatalities in large populations and has caused a trend to measure dose limits for the public not against the magnitude of the natural radiation exposure and its geographic variations, but against the numerical risk estimates. In reaction to this development, opposing claims are being made of a threshold in dose for deleterious health effects in humans. In view of the growing polarization, ICRP is now exploring a new concept “controllable dose” that aims to abandon the quantity collective dose, emphasizing, instead, individual dose and, in particular, the control of the maximum individual dose from single sources. Essential features of the new proposal are here examined, and it is concluded that the control of individual dose will still have to be accompanied by the avoidance of unnecessary exposures of large populations, even if their magnitude lies below that acceptable to the individual. If a reasonable cut-off at trivial doses is made, the collective dose can remain useful. Misapplications of collective dose are not the deeper cause of the current controversy; the actual root is the misrepresentation of the LNT-assumption as a scientific fact and the amplification of this confusion by loose terminology. If over-interpretation and distortion are avoided, the current system of radiation protection is workable and essentially sound, and there is no need for a fruitless LNT-controversy. The new concept of controllable dose promises simplifications and improvements, but any major change of principles needs to be carefully considered in a broad discussion that ICRP is presently seeking.