Modelling of continuous low dose rate and accelerated fractionated high dose rate irradiation treatments in a human glioma cell line

The Incomplete-Repair model of Thames in its original and in its two-repair processes forms is used to analyse continuous and fractionated irradiation of a glioma cell line treated in vitro. Furthermore, the Incomplete-Repair model is rederived based on the linear-quadratic model bearing a cubic term. Our results show a potentially enhanced but nonsignificantly improved fit to the data when comparing the cubic to the original form of this model. The repair halftime values showed a decrease, followed by an increase, as a function of small doses (<1.5 Gy) per fraction. This is observed using both the original and the cubic forms of the model. We propose this behaviour to be due to an induced resistance of the repair system followed by a saturation process. Two-repair processes were not seen directly due to the large scatter in the fast and the slow components of repair. Repair half-time values are estimated for various dose per fraction protocols using the original and extended forms of the Incomplete-Repair model. Two-repair processes that are consistent as a function of dose per fraction were not detectable in a glioma cell line treated in vitro.