The relative biological effectiveness of 160 MeV protons--II. Biological data and their interpretation in terms of microdosimetry.

The radiobiological effectiveness of 160 MeV protons was measured relative to -Co y-rays, using Chineee hamster cells cultured in o&o. Separate experiments were performed witb cells irradiated in sWpem&m, or attached to plastk tisslre culture flasks. Proton irradiations were performed in the incident plateau of the depth dosepro6Uc~niththeBrPggpenksprendouttocoverlOcls.Inallcrrscstberdstlveblde%esleff~~ (RBE) for protons relative to gamma rays was 1.2 for doses in excess of abont 24M rad. The attswhed cell experiments indkate an in creasing RBE at low doses, whkh is consistent with the microdosimetric measurements.