Medical Radiology and Radiation Safety. 2014. Vol. 59. No. 5. P. 64-71
REVIEW
S.V. Osovets
Quantitative Assessment and Classification of Threshold Radiation Values
Southern Urals Biophysics Institute, Ozyorsk, Chelyabinsk region, Russia. E-mail: This email address is being protected from spambots. You need JavaScript enabled to view it.
ABSTRACT
Purpose: A mathematical description of general methods for risk and threshold assessment, classification of these values based on their dose- and time-distribution parameters associated with deterministic effects.
Results: A standard Weibull distribution containing 2 parameters (D50 median effective dose and a shape parameter) is used as a baseline distribution to describe deterministic effects associated with dose.
Methods for assessment of threshold values and corresponding uncertainties are classified and quantitatively described in details. The classification of threshold values based on assessment methods is presented as follows:
- methods for assessment of quantile (restricted) thresholds;
- methods for assessment of thresholds based on densities or functions of distributions by doses or time parameters;
- methods for assessment of a priori (postulated in a mathematical model) threshold values.
Effectiveness and feasibility of the presented methods for threshold assessment are demonstrated by the example of associations with various deterministic effects. Relative uncertainties of thresholds are derived using different methods as well.
Conclusions: Various methods for assessment of threshold values of deterministic effects are summarized and threshold classification is presented. Quantile (restricted) thresholds (1 % and 5 %) are shown to be useful for radiation safety purposes. However the so-called applicative thresholds for purposes of radiation medicine and radiation safety should be described using a relative bound between a main group and a group of comparison. The corresponding methods are presented for assessment of these bounds. Uncertainties of threshold values are calculated.
A concept of a priori thresholds is introduced; the methods for their assessment are applicable both to deterministic and stochastic effects. In general the considered methods for assessment of threshold values are focused on various tasks of radiation safety and medicine, and in this regard they complement each other rather than contradict.
Key words: radiation doses, deterministic effects, risk assessment, threshold classification, relative uncertainty, threshold