Relative biological efficiency of ionizing radiation that is used in radiation therapy of cancer patients
DOI:
https://doi.org/10.15407/dopovidi2019.12.101Keywords:
cell cycle stage, chromosome aberrations, fast neutrons, radiation therapy, relative biological efficiencyAbstract
Fast neutrons, which are characterized by high ionization density and penetrate deeply into a tumor, are of the greatest practical importance in clinical radiobiology and radiation therapy of cancer patients. However, the side effect of their action is the development of late severe radiation complications. Therefore, the study of the patterns of formation of the relative biological efficiency (RBE) of neutrons of a specific energy depending on the dose and degree of radio sensitivity/radio resistance of irradiated cells (the position in the mitotic cycle) is justified because of its importance. Objective of the study: to study the RBE of fast neutrons depending on their energy (6 and 22 MeV), absorbed dose, and stage of mitotic cycle of human peripheral blood lymphocyte culture (cytogenetic study). It is shown that the highest values of the RBE with the energy of 6 MeV (in the dose in terval 0.32-2.67 Gy) for chromosome aberration yield are observed when exposed to the lymphocyte culture in the G2-stage, the lowest — when exposed in the S-stage. The intermediate position is occupied by the values of the RBE of neutrons at irradiation of the lymphocyte culture in the G0- and G1-stages. In the dose interval 0.2-4.0 Gy, the value of the RBE neutrons with the energy of 22 MeV is the most significant in the dose interval 0.2-2.0 Gy, which is commonly used in clinical practice. As the dose of the radiation exposure increases, the RBE of neutrons with both energies decreases. Thus, the maximum biological efficacy of fast neutrons is manifested by irradiation in the low-dose interval and in the most radiosensitive state of cells (the G2-stage of mitotic cycle). Currently, the priority of neutron therapy for the treatment of cancer patients has not been preserved in Ukraine and, accordingly, there is no concept of its further development. The data obtained by us indicate that it is ad visable to conduct pre-clinical biodosimetric studies to clarify the RBE at the therapeutic use of radiation with high ionization density in clinical oncology.
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