The application of the linear quadratic model to compensate the effects of prolonged fraction delivery time on a Balb/C XXXX : An in vivo study.

@entity19 @entity5 @entity0
UNASSIGNED: Purpose To investigate the effect of increasing the overall treatment time as well as delivering the compensating doses on the Balb/c @entity0 . Materials and methods A total of 72 @entity19 were divided into two aliquots (classes A and B) based on the initial size of their induced @entity5 . Each class was divided into a control and several treatment groups. Among the treatment groups, group 1 was continuously exposed to 2 Gy irradiation, and groups 2 and 3 received two subfractions of 1 Gy over the total treatment times of 30 and 60 min, respectively. To investigate the effect of compensating doses, calculated based on the developed linear quadratic model (LQ) model, the remaining two groups (groups 4 and 5) received two subfractions of 1.16 and 1.24 Gy over the total treatment times of 30 and 60 min, respectively. The growing curves, @entity5 Growth Time (TGT), @entity5 Growth Delay Time (TGDT) and the survival of the animals were studied. Results For class A ( @entity5 size    <=   30   mm(3)), the average @entity5 size in the irradiated groups 1-5 was considerably different compared to the control group as one unit (day) change in time, by amount of   -160.8,   -158.9,   +39.4 and   +44.0, respectively. While these amounts were   +22.0,   +17.9,   -21.7 and   -0.1 for class B ( @entity5 size   >=    400   mm(3)). For the class A of animals, the TGT and TGDT parameters were significantly lower (0    <=   0.05) for the groups 2 and 3, compared to group 1. There was no significant difference (p   >   0.05) between groups 1, 4 and 5 in this class. There was no significant difference (p   >   0.05) between all the treated groups in class B. Conclusions Increasing total treatment time affects the radiobiological efficiency of treatment especially in small-sized @entity5 . The compensating doses derived from the LQ model can be used to compensate the effects of prolonged treatment times at in vivo condition.
