Chromosome aberration frequencies in human lymphocytes irradiated in a phantom by a mixed beam of fission neutrons and gamma-rays.

PURPOSE: To provide further information on the existence of a significant quadratic component of the dose response relationship for the production of dicentrics in human lymphocytes by mixed fission neutron and gamma-ray irradiation, which has been observed previously employing the same beam under free-in-air conditions.

MATERIALS AND

METHODS

Irradiation of blood samples and dosimetry was performed at 2 cm depth in a polymethyl methacrylate (PMMA) phantom of 16 cm side-length where the PMMA material fully surrounded the blood specimen. Chromosome analysis was carried out exclusively in complete first division metaphases.

RESULTS

Dicentric yields induced by absorbed doses between 0.043 and 2.68 Gy fit a linear-quadratic model with a quadratic coefficient significantly different from zero. The distribution of dicentrics is overdispersed compared to Poisson at lower doses, but is poissonian at higher doses.

CONCLUSION

The presence of a significant quadratic dose response coefficient for dicentrics, both for free-in-air and phantom irradiation, is caused by the various degraded fission spectra that produce neutrons or recoil protons over a broad energy range, rather than by the gamma-ray component of the beam.