Frequency of chromosome aberrations (dicentrics and rings) at low doses (dashed line) and at higher doses (solid line).

The probability of an exchange aberration is proportional to dose (D) and the square of the dose (D²), respectively. At low doses, a secondary electron resulting from absorption of an x-ray photon induces breaks in each of the chromosomes. At high doses, secondary electrons from multiple atoms induce these chromosome breaks. The net effect of a break is interchange of chromosomal material, resulting in the formation of a dicentric and an acentric fragment.

Reprinted with permission from