Rbe For Inactivation Of Tumoural And Normal Cell Lines Of Human Origin Irradiated With Low-Energy Protons

Inactivation of four human cell lines, two deriving from tumours (SQ20B and SCC25) and two from normal tissues (H184B5 F5-1 M/10 and HF19), have been studied after irradiation with low energy protons of various LET in the range 8-28 keV/mu m. The cells that were the most resistant to X-or gamma-rays also appeared the most resistant to protons. However, difference in radioresistance decreased with increasing proton LET. This is due to the fact that RBE of high-LET protons was higher for the cells resistant to sparsely ionising radiation than for the sensitive ones, i.e., radioresistance was decreased at high LET. This phenomenon was more pronounced in tumour cells. This enhanced biological effectiveness in tumours, resistant to conventional radiation, may be a further favourable feature for the use of protons in radiation therapy.