Research on the effect of fractionated irradiation with variable fraction sizes on the mice bearing SK-BR-3 tumor

Objective: To analyze the effect of fractionated irradiation with variable fraction sizes (VFS) on the mice bearing SK-BR-3 tumor. Methods: The mice were divided into six groups, four groups were irradiated with different VFS protocols, one group was irradiated with constant fraction size(CFS) protocol, one group was non-irradiated as a comparing group. For these groups of mice, the average surviving period (ASP) and the change of tumor volume were observed and compared. Results: The ASP of irradiated groups are all longer than that of non-irradiated group, and the difference of ASP between these groups have the statistical significance respectively. Also the ASP of the groups irradiated with VFS protocols are all longer than that of the group irradiated with CFS protocol, but the difference is of no statistical significance. For the mice irradiated with decreasing fraction sizes, the ASP is longer than that of the mice irradiated with corresponding increasing fraction sizes, but the difference has no statistical significance. For these six groups, the tumor volumes are all increasing in this experiment, and the increasing speed of non-irradiated group is faster than that of all the other irradiated groups. Conclusion: For the same absorbed dose, the VFS irradiation protocol, especially the protocol with decreasing fraction sizes can prolong the ASP of mice, so perhaps this kind of protocol can be used in clinics to improve the effect in radiotherapy. (authors)