| IntroductionAs a new and important radiotherapy technique,intensity-modulated radiation therapy(IMRT) has been widely used in the clinic,but it requires longer time to deliver for one treatment session.ObjectiveThe purpose of this study is to investigate the radiobiological effects of A549 cell line irradiated by IMRT model and research the effect of different delivery time with same dose on the tumor growth delay in nude mice implanted with A549 cell.MethodsThe in vitro assay is consist of three parts.Partâ… :The radiobiological characteristics of CNE and A549 cell lines were studied with standard clonogenic assays,using standard liner-quadratic model to fit the dose-survival curves.Partâ…¡:a total dose of 8Gy was given in two fractions with different interfraction intervals, compare the differences of cell surviving fractions(SF).Partâ…¢:fractioned irradiation of 2Gy,2Gy×2,2Gy×3,2Gy×4 were given with one fraction per day simulating clinical dose-time-fractionation pattern in 2min,20min and 40min per fraction.In the in vivo assay,we used 64 nude mice implanted with A549 cell in the back legs and the experiment started when the transplanted tumor diameter reached 0.8 to 1cm.15Gy was divided into different subfractions.64 nude mice were randomized into 8 groups:the normal control group,the single fraction with 15 Gy group,the two subfractions with 20min interval group,the five subfractions with 5min interval group, the nine subfractions with 2.5min interval group,the two subfractions with 40min interval group,the five subfractions with 10min interval group,the nine subfractions with 5min interval group.Record the maximal and minimal diameters of the tumor to observe the tumor growth tendency and the tumor growth delay. ResultsTheα/βof A549 is 12.41Gy;the cell surviving fractions increased when the interfraction interval was longer,The value of SF2 was 0.0243 in 2min irradiation group,was 0.0296 in 20min irradiation group,and increased to 0.0359 in 40min irradiation group.The tumor growth delay of groups with prolonged delivery time 40min were shorter than the group with single fraction of 15 Gy(P＜0.05).The tumor growth delay of groups with prolonged delivery time 20min were longer or tend to be longer than that of groups with prolonged delivery time 40min(P＜0.05 or P=0.054).There were no significant differences between groups with same delivery time(P＞0.05).ConclusionsThe prolonged fraction delivery time would significantly decrease the radiobiological effects,it is strongly recommended that keep the delivery time as short as possible.
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