Lethal Effect and Potentially Lethal Damage Recovery in Cultured Mammalian Cells Irradiated by Neutron-capture Beams

Summary

Cell killing and potentially lethal damage (PLD) recovery in Hela cells were examined after irradiation in suspension using a ¹⁰B neutron-capture beam. Thermal-neutron irradiation in the medium containing from 0·09 to 9 mm boron-10 (0·9–90 µg/g ¹⁰B, 90 per cent enriched boric acid) resulted in steeper survival curves than in the boron-free medium. The relative biological effectiveness (r.b.e.), expressed as the D₀ ratio, increased from 2·2 ± 0·1 for the control without boron-10 to 5·4 ± 0·3 in the medium containing 0·9 mm boron-10. The r.b.e. value was 5·2 ± 0·5 at a boron-10 concentration of 9 mm, and did not increase when the boron-10 concentration was increased from 0·9 to 9 mm. It was suggested that the observed plateau of r.b.e. at boron-10 concentrations higher than 0·9 mm was due to the dominancy of the ¹⁰B(n,α)⁷Li reaction for dose accumulation. PLD recovery after the neutron irradiation containing 0·9 mm boron-10 was not observed, while a small effect was observed after irradiation in the thermal neutron beam, although much less than after gamma rays. The results show that the neutron-capture beam is an excellent beam for radiotherapy if the boron-10 concentration in tumour cells could be elevated to about 1 mm.