Induction and repair of DNA lesions in cultured human melanoma cells exposed to a nitrogen-ion beam.

Induction and repair kinetics of DNA lesions after exposure to nitrogen ions (N-ions) were studied in comparison to those after 180 kVp X-rays. DNA lesions in human melanoma cells (HMV-I) irradiated with 95 MeV N-ions (0-6 Gy, l.e.t.D = 530 keV micron-1 or with X-rays (0.9 Gy) were assayed by alkaline elution. The N-ion r.b.e. for DNA lesion induction was approximately 0.7. About 85 per cent of the lesions induced by N ions were rejoined with a time-course similar to the rejoining of DNA lesions produced by X-rays. These lesions were considered to be induced by delta-rays around the N-ion tracks. The fraction of residual DNA lesions remaining after a 6 h post-irradiation incubation was higher for N-ions than for X-rays. Unlike the case for X-rays, DNA-protein crosslinks were included in the residual DNA lesions after N-ion irradiation.