Radiobiological properties of high-energy cyclotron-produced neutrons used for radiotherapy

Radiobiological properties of high-energy cyclotron-produced neutrons were investigated. The survival curve for mammalian cells exposed to 35 MeV neutrons has an appreciable shoulder, but exhibits a significant initial slope at low doses. Split-dose experiments, using doses comparable to the daily fractions of neutron therapy, indicate no repair of sublethal damage. The nitroimidazoles, and particularly Flagyl, have been shown to selectively sensitize hypoxic cells to the effects of x rays. Experiments demonstrated that Flagyl is equally effective in reducing the oxygen enhancement ratio for high-energy neutrons. Hypoxic sensitizers must be regarded as an adjunct to neutron therapy, rather than as a competitor. (auth)