[ RadSafe ] dose RATE is the decisive variable

Rainer.Facius at dlr.de Rainer.Facius at dlr.de
Fri Sep 1 04:54:57 CDT 2006

The recent paper below elaborates a seemingly trivial principle, i.e., the response of (not only nonlinear) systems capable of intrinsic counteractive measures to compensate external stimuli is not primarily determined by the stimulus' amplitude but rather by the ratio between the stimulus' temporal gradient and the characteristic 'response' time of the system's feed-back control systems - as long as its capacities are not overstrained. Thus the rate is not a parameter - as conventionally it is conceived of - but a primary independent variable. 

Applying this 'law' to that subset of 13 epidemiological studies which have been compiled by UNSCEAR 2000 and which provide the necessary data to pursue this approach (no cherry picking!), the authors arrive at a rather provocative result. I have prepared a graph from their table similar to their own but somewhat enhanced to facilitate the contemplation and mental digestion of these data which at face value would suggest that a threshold (or even the region for beneficial effects in terms of cancer mortality) extends to much higher chronic exposures (rates) than so far publicly discussed (e.g. the 5 mrem annually invoked the other day by Bernard Cohen). I attach that graph as PDF, hoping it will pass the moderator.

Enjoy, Rainer

Gregoire O, Cleland M.
Novel approach to analyzing the carcinogenic effect of ionizing radiations <http://www.ingentaconnect.com/content/tandf/trab/2006/00000082/00000001/art00002>  
International Journal of Radiation Biology 82#1(2006)13-19

Purpose: Cancer incidence of ionizing radiations exposure is considered to be proportional to the absorbed dose. However, there are disagreements between substantial amounts of epidemiological studies. In this study, we question the basic relationship of the risk estimate with total accumulated dose, and reanalyse available data on the basis of a daily dose concept. 

Materials and methods: The data analysed were relative mortality risk from all cancers vs. total-body dose on a daily basis. References have been selected on the basis of objective criteria. 

Results: We found that this relationship removes major discrepancies. It revises estimates of low-level exposures, with consequences regarding nuclear power plants safety, wastes management, medical applications or homeland security. 

Conclusions: The idea that the dose rate may have a significant impact on health effects of ionizing radiations is not new, but has always been considered as a parameter in models based on integrated dose. The novel approach in this paper is to consider the primary relevant parameter as an average of dose rate over a time period of one day. This is an argument to revise the whole philosophy in radioprotection, and place regulatory limits on specific locations instead of annual limits relevant to individual persons. 


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