E Schmid1, H Schraube, M Bauchinger. 1. Institute of Radiobiology, GSF, National Research Center for Environment and Health, Neuherberg, Germany.
Abstract
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.
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.
Authors: Franz M Wagner; Peter Kneschaurek; Anton Kastenmüller; Birgit Loeper-Kabasakal; Severin Kampfer; Harald Breitkreutz; Wolfgang Waschkowski; Michael Molls; Winfried Petry Journal: Strahlenther Onkol Date: 2008-12-24 Impact factor: 3.621