Statistical Interpretation of the Overdispersed Distribution of Radiation-Induced Dicentric Chromosome Aberrations at High LET

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Abstract
Whether overdispersion of the chromosome aberration number per cell results from multiple aberrations per particle traversal is mathematically investigated. At a given absorbed dose, Poisson distributions are assumed for the number of ionizing particles traversing a cell nucleus and for the number of aberrations induced by a single particle traversal. The resulting distribution of the number of aberrations per human lymphocyte is the Neyman type A distribution, a special case of the generalized Poisson distribution. This function is generally overdispersed. Its relative variance 1 + .lambda. is determined by the expectation value .lambda. of aberrations per particle traversal, typical for high LET [linear energy transfer]; regular dispersion results at low LET. Neutrons and .alpha. particles agree with this theory. The formalism provides a method to determine the efficiency of aberration induction per particle traversal, .lambda. from the frequency distribution of aberrations.