Purpose: It has been proposed previously that the ratio of complete to inco
mplete translocations as seen by fluorescence in situ hybridization (FISH),
the S value, can be a cytogenetic fingerprint of exposure to radiation of
different qualities. Results from a previous study suggested that the S val
ue is similar to 10 for sparsely ionizing radiations such as X- and gamma-r
ays, and similar to 2 for densely ionizing radiations. Based on FISH data o
f atomic-bomb (A-bomb) survivors, which showed an S value of 3.25, a signif
icant neutron component to A-bomb radiation was suggested. To examine the p
ossibility, the present in vitro study was conducted using X-rays.
Materials and methods: Human blood lymphocytes were exposed to X-rays and f
irst metaphases were examined with FISH using DNA probes for chromosomes 1,
2 and 4.
Results: The S value was 3.16 for X-rays, which differs from similar to 10
as reported previously, and not larger than the 3.25 obtained from the bloo
d lymphocytes of A-bomb survivors.
Conclusions: S values seem to vary among laboratories even after exposure o
f cells to sparsely ionizing radiations. Data from this study show that S v
alues are not a signature for a significant contribution of neutrons to the
radiation dose received by A-bomb survivors in Hiroshima.