Proximity effects for chromosome aberrations measured by FISH

A Monte Carlo simulation computer program for radiation-produced chromosome aberrations, based on the breakage-and-reunion model, was extended to include proximity effects due to locailization of chromosomes and limited range for break-break interactions. Two adjustable parameters were used. One corresponds to total dose; the other determines proximity effects by specifying the number of 'interaction regions' in a cell nucleus. The use of additional adjustable parameters was avoided by assuming randomness of break induction and aberration production. FISH chromosome painting data were obtained from 1. 9 Gy 60Co gamma-raysirradiated human lymphocytes. The data were compared with the computer simulation results, taking individual chromosome lengths into account. With about 13 interaction regions, agreement between the experiment and the simulation was good, even when detailed categories of damage were scored. An estimated average dsb-dsb interaction distance, based on 13 interaction regions, is about 1.3 mu...