Lack of hyper-radiosensitivity and induced radioresistance and of bystander effect in V79 cells after proton irradiation of different energies.

A huge body of evidence about the hyper-radiosensitivity and induced radioresistance (HRS/IRR) phenomena and the bystander effect (BE) is reported in the literature, in many cell types and in terms of various biological endpoints, after high- and low-linear energy transfer irradiation. However, the mechanisms underlying these effects together with their inter-relationship, and the correlation of HRS/IRR and BE phenomena with radiation quality are not yet well established and elucidated. To study these phenomena, the radiation response of V79 cells has been evaluated in terms of cell survival after irradiation with broad beams of 7.7- and 28.5-keV μm(-1) protons. HRS/IRR has been investigated also in terms of micronuclei and chromosomal aberration induction. The presence of BE has been investigated with a 'partial shielding irradiation' system, which prevents the irradiation of 35 % (on average) of the cell population. No clear evidence of HRS/IRR, nor of a significant BE response, can be identified in the low-dose region of V79 dose-response curves after proton irradiation of different energies.