Speaker
Dr
Ekaterina Koryakina
(Medical Radiological Research Center)
Description
Cytogenetic studies of a new neutron device ING-031, pulsed neutron generator with sealed tube, were carried out using G0 human lymphocytes as a test-system. The generator produced (D,T) neutrons with the energy of 14 MeV at the frequency of 1-100 Hz. Samples of whole blood were irradiated in stacked up glass Carrel flasks under proton equilibrium conditions. Thus, all samples were irradiated simultaneously, the dose and dose rate depending on the generator target to blood sample distance. Experiments were carried out at two frequencies, 5 and 50 Hz, in the dose range of 0.1-1.2 Gy. Doses were measured with fission foil detectors and calculated with Monte Carlo codes. Metaphase preparations of the 1st mitosis were conventionally stained. Aberrations recorded were dicentrics, centric and acentric rings, and excess acentric fragments.
Conventional fitting of experimental data points for dicentrics and total aberrations produced linear regression curves with no difference between pulsed irradiation and continuous irradiation modes (previously obtained data) as well as between 5 and 50 Hz irradiation. However, thorough point by point inspection of chromosomal aberrations (CA) yield per unit neutron dose revealed the well-known, in photon radiobiology, pattern of hypersensitivity-induced radioresistance (HS-IR) dose-effect dependence: low CA yield, then sharp rise of CA at doses of 0.12-0.15 Gy (HS) followed by a (quasi)plateau (IR) up to 0.3-0.4 Gy, and finally transition to a regular linear-quadratic dependence. This is, perhaps, the first presentation of HS-IR phenomenon in neutron cytogenetic studies.
When the data obtained were arranged as the CA yield per 1 Gy versus neutron dose rate at that point, another well-known dependence was observed: inverse dose rate effect. The CA yield (per 1 Gy) increased by a factor of 2.5 with neutron dose rate decrease from 60 mGy to 0.3 mGy. Earlier the inverse dose rate effect was reported by Hill et al. for C3H 10T1/2 cells transformation following fission neutron irradiation nearly at the same dose rate range. Since RBE>1 for cell transformation, it suggests that a certain type of CA (translocations?) was involved in the both studies.
To conclude, two new phenomena were observed at low doses/low dose rates of 14 MeV neutrons: zones of hypersensitivity-induced radioresistance on the initial part of dose curves for CA induction in G0 human lymphocytes, and inverse dose rate effect for the same test-effect.
Primary author
Dr
Ekaterina Koryakina
(Medical Radiological Research Center)
Co-authors
Dr
Olga Potetnya
(Medical Radiological Research Center)
Prof.
Stepan Ulianenko
(Medical Radiological Research Center)
Dr
Vladimir Potetnya
(Medical Radiological Research Center)
