Applicability of the linear-quadratic model to single and fractionated radiotherapy schedules: An experimental study

The aim of this study was to examine the applicability of the linear-quadratic (lq) model to single and fractionated irradiation in emt6 cells. first,the α/β ratio of the cells was determined from single-dose experiments,and a biologically effective dose (bed) for 20 gy in 10 fractions (fr) was calculated. fractional doses yielding the same bed were calculated for 1-,2-,3-,4-,5-,7-,15- and 20-fraction irradiation using lq formalism,and then irradiation with these schedules was actually given. cell survival was determined by a standard colony assay. differences in cell survival between pairs of groups were compared by t-test. the α/β ratio of the cells was 3.18 gy,and 20 gy in 10 fr corresponded to a bed3.18 of 32.6 gy. the effects of 7-,15- and 20-fraction irradiation with a bed 3.18 of 32.6 gy were similar to those of the 10-fraction irradiation,while the effects of 1- to 5-fraction irradiation were lower. in this cell line,the lq model was considered applicable to 7- to 20-fraction irradiation or doses per fraction of 2.57 gy or smaller. the lq model might be applicable in the dose range below the α/β ratio. © 2013 the author. published by oxford university press on behalf of the japan radiation research society and japanese society for radiation oncology.