The influence of the time interval between the exposure to different quality radiation on murine B-16 melanoma cells survival

In modern radiotherapy schemes, radiations of different quality are used. Depending on the technical conditions, the irradiation sequence and interval between the exposures can be varied. For the combined gamma-neutron action, the dose contribution of neutrons varies from 20 to 40%. Taking into account the biophysical characteristics of charged particles and the processes of cellular damage and recovery, the dependence of biological effect on irradiation scheme is supposed. The influence of time interval between the irradiations of murine melanoma B-16 cells with 60-Co g-rays with an average energy of 1.25 MeV and neutrons with an energy of 14.1 MeV was investigated. Portable neutron generator (NG-14) of continuous action, developed at the All-Russian Research Institute of Automation. N.L. Dukhova (Moscow) was a source of neutron radiation. Photons were provided by “Luch” installation. Irradiation was carried out in two sequences: first gamma radiation, then neutron (g-n), and vice versa (n-g); the interval between exposures was 30, 60 and 120 minutes. The effectiveness of irradiation was assessed by the cell survival according measured by clonogenic assay. It is shown that the biological effectiveness of neutrons and photons combined action did not depend on the sequence of irradiation. An increase in the time interval between irradiations (from 30 to 120 min) was accompanied with the growth of cell survival. Thus the time interval between promote the repair of non-lethal DNA damages. According to these results the most acceptable scheme of combined radiotherapy with neutrons and photons should include no more than 1 hour time interval between the irradiations with these agents.