COMET ASSAY STUDY OF DNA-DAMAGE AND REPAIR OF TUMOR-CELLS FOLLOWING BORON NEUTRON-CAPTURE IRRADIATION WITH FAST D(14)+BE NEUTRONS

We compared the amount of radiation-induced DNA damage and the extent of DNA repair in human melanoma cells (MeWo) using the 'comet assay' a fter neutron, boron neutron capture and X-irradiation. Using a colony- forming assay it was shown earlier that lethal effects in tumour cells treated with fast neutrons may be increased by the neutron capture re action B-10(n,alpha)Li-7. The effectiveness of borun neutron capture I n killing tumour cells depends on the number of B-10 atoms delivered t o the tumour, the subcellular distribution of B-10 and the thermal neu tron fluence at the side of the tumour. Using the 'comet assay' the DN A damage of fast neutrons (mean energy 5.8 MeV) was shown to be signif icantly greater than for the same absorbed dose of X-rays. The presenc e of 600 ppm B-10 (boric acid H-3 (BO3)-B-10) in the cell medium durin g irradiation with d(14) + Be neutrons in a phantom enhances the DNA d amage by 20% compared with neutron irradiation alone. After DNA damage induction by neutrons and neutron capture of boron, the DNA repair ca pacity of the MeWo cells is significantly reduced in comparison with X -irradiation resulting in proportionally more residual DNA damage afte r 180 min of repair time.