CABAS: a freely available PC program for fitting calibration curves in chromosome aberration dosimetry.

The aim of biological dosimetry is to estimate the dose and the associated uncertainty to which an accident victim was exposed. This process requires the use of the maximum-likelihood method for fitting a calibration curve, a procedure that is not implemented in most statistical computer programs. Several laboratories have produced their own programs, but these are frequently not user-friendly and not available to outside users. We developed a software for fitting a linear-quadratic dose-response relationship by the method of maximum-likelihood and for estimating a dose from the number of aberrations observed. The program called as CABAS consists of the main curve-fitting and dose estimating module and modules for calculating the dose in cases of partial body exposure, for estimating the minimum number of cells necessary to detect a given dose of radiation and for calculating the dose in the case of a protracted exposure. The program is freely available at http://www.pu.kielce.pl/ibiol/cabas.

Presenting statistical uncertainty on cytogenetic dose estimates.

Cytogenetic dosimetry results are customarily accompanied by 95% confidence limits and the derivation of these limits is discussed. Simply presenting values of the best estimate of dose and 95% limits assumes that recipients of dosimetry reports, possibly the patients themselves, have a sufficient grasp of statistics to comprehend the concept of uncertainty. Two further methods have been developed to aid improved understanding for the lay person. The first method, particularly useful for suspected low doses, presents a simple odds ratio indicating that the results favour either zero dose or that suspected; for example, from an unexpected dose recorded on a badge. The second method, described fully here for the first time, uses a graphical illustration of a normalised distribution of dose so that one may visualise the area beneath a curve that represents the probability that the dose lies within various bounds.