Estimation of relative biological effectiveness of 6 and 22 MeV neutrons and Cs γ-rays based on the analysis of chromosome aberrations in human peripheral blood lymphocytes

Abstract

Aim

This investigation presents the estimation of cytogenetic injury in human peripheral blood lymphocytes and its dependence on the dose and quality of ionizing radiation applied in radiotherapy of cancer patients with the purpose of calculating RBE values for different radiation sources in the dose range under study.

Materials/Methods

Cytogenetic dosimetry was carried out at an exposure of human lymphocyte cultures to ¹³⁷Cs and ⁶⁰Co therapeutic sources and neutrons with average energies of 6 and 22 MeV.

Results

Increase in dose reduces RBE values of ¹³⁷Cs γ-irradiation, which in the range of doses investigated (0.3–5.0 Gy) vary between 3.5–1.3, respectively. Thus the difference in RBE values can be most accurately determined in the 0.5–2.0 Gy dose interval usually used in radiotherapy. Comparative estimation of fast neutron RBE values showed that 6 MeV neutrons give significantly higher yields of chromosome aberrations as compared with 22 Mev neutrons. It was shown that cytogenetic effectiveness has a tendency to decrease with the increase in the depth of the water phantom. The largest effect was observed at the depth of up to 6 cm.

Conclusions

The results of our pre-clinical studies indicate that radiation-induced effects simultaneously depend on different irradiation parameters such as dose, energy and the depth of the irradiated biological object, which should be taken into account in radiotherapy of cancer patients.