Exstended biological dosimetry of the irradiation emitted by NG-12I neutron generator

Purpose: The aim of the present work was to carry out biological dosimetry of the irradiation, generated by the installation NG-12 I, on basis of stem hematopoietic cells survival in СВА line mice assessed with the test of the exogenous colony formation. Material and methods: The Center of Neutron Therapy of the Chelyabinsk Regional Oncologic Centre located in the Federal Nuclear Centre (Snezhinsk), carries out the photon-neutrons therapy of oncologic patients with the use of gamma-installation ELLIT-80 (dose rate is 2.51 Gy/minute, gamma-field inhomogeneity in working space is no more than 10 %) and neutron generator NG-12 I (average energy of neutrons in working space is 10.5 MeV, neutrons dose rate is 11.5 rad/minute, gamma-radiation fraction is 4-8 %, field inhomogeneity is no more than 15 %). Results: The results of our experiments have shown that dose D0 for colony forming units in the spleen in CBA mice after single acute gamma irradiation was 0.88 Gy, whereas after fractionated gamma-irradiation it was 1.99 Gy (twice as much as D0 for acute irradiation). It means that post-radiation restoration progresses in the time between fractions. The dose D0 for colony forming units in the spleen in CBA mice after single acute neutron irradiation and after fractionated irradiation was 0.6 Gy and 0.65 Gy respectively, i.e. those indices practically have not changed after fractionated neutron irradiation. That fact suggests the absence of significant restoration of radiation-induced defects after neutron irradiation. The rate of relative biological effectiveness (RBE) for radiation of installation NG-12I, defined as a ratio of equal effective doses (in our research D0 was used) was 1.47 for the acute neutron irradiation and 3.06 for the fractionated neutron irradiation. Conclusion: the obtained data allows to define the total dose and single fraction dose of a neutron irradiation of installation NG-12I for photon-neutron therapy for the complex clinical situations in cancers.