Radiosensitivity variations in human tumor cell lines exposed in vitro to p(66)/Be neutrons or 60Co gamma-rays

Neutron therapy should be beneficial to patients with tumor types which are resistant to photons but relatively sensitive to high-LET radiation. In this work the potential therapeutic gain of a clinical neutron beam is evaluated by quantifying the variations in radiosensitivity of different cell lines to neutrons and photons.Different cell lines were exposed in vitro to p(66)/Be neutrons or 60Co gamma-rays. Micronuclei frequencies in binucleated cells and surviving fractions were determined for each cell type.Following exposure to either 1 or 1.5 Gy neutrons, micronuclei frequencies were significantly correlated with that observed for 2 Gy photons. A weak but significant correlation between the variation in neutron RBE values, determined from survival curve inactivation parameters and the mean inactivation doses for photon exposures, was also established.It is concluded that although neutron and photon sensitivities are related, the use of this high energy neutron source may constitute a potential therapeutic gain for tumor types that can be identified as very resistant to photons. Considering that a definitive oxygen gain factor has been established for this neutron beam the observed therapeutic gain is expected to be further enhanced in tumors where hypoxia protects cells from conventional radiation damage.