A Comparative Study Of Biological Effects Between LQ Formula Calculated And Experimental Measured With Hypofractionated

Part I:Biologically effective dose(BED) vs the biological effects by experimental measuredPurpose:To examine the applicability of the linear-quadratic(LQ) formalism and BED to single and hypofractinated radiation doses.Methods and Materials:The MCF-7 human breast cancer and Anip973 lung cancer exnografts were used. They recevied various fractionated irradiation(200cGyx5/w, 300cGyx5/w,400cGyx3/w,400cGyx5/w,600cGyx5/w, single dose, with BED 72Gy or 78Gy). Using the LQ formalism, equivalent doses for the hypofractionated doses were calculated. The total observation time was 9 weeks to 24 weeks. They were then compared with these measurement indexes:tumor formation rate, short-term tumor control rate, long-term tumor control rate, tumor inhibiton rate, tumor recurrence time, maximum diameter of the bottom of solid, mortality, survival.Results:Each experimental group has same BED, but their theoretical dates were not very consistent with the measured datas. BED72Gy, the human lung cancer mortality in each subclinical tumor irradiation regimen was 100%, and their survival were differences:the 200cGyx5/w group was 63 days, the hypofractionated regimen 300cGyx5/w was 69 days,400cGyx3/w was 61 days,600cGy×5/w was 69 days, single irradiation regimen was 65 days and the control group was 56 days, respectively. The hypofractionated regimen 300cGyx5/w has the longest average survival time; BED78Gy, the biological effects of human breast subclinical tumors fractionated regimens were significantly different:the 200cGyx5/w group, the hypofractionated regimen 300cGyx5/w and 400cGyx3/w have same short-term tumor control rate, but their long-term tumor control rate were 25%、100% and 75%, respectively; BED72Gy, the human lung adenocarcinoma xenografts in nude mice long-term tumor control rates were: the 200cGyx5/w group was 25%, hypofractionated regimen 300cGyx5/w was 25%, 400cGyx5/w was 25%, hypofractionated regimen 600cGyx5/w was 75% and the single irradiation regimen was 0%, respectively. At the end of 24 weeks each group tumor inhibition rates were:the 200cGy×5/w group was 69%, the hypofractionated regimen 300cGyx5/w was 63%,400cGy×5/w was 72%,600cGy×5/w was 79%, single irradiation regimen was 35%, respectively.Conclusion:Conversion of 2Gy to hypofractionated radiation doses and single dose using the LQ formalism could underestimate or overestimate the effect of hypofractionated radiation.Part II:Measurement of radiobiology parameters of lung cancer cells in vitroPropose:To measure the radiation response characteristics of Anip973 cell line by evaluate the radiobiology parameters of Anip973 cells in vitro. To provide experimental basis at the cellular level for investigating the mechanisms of measured biological effects among the same BED and different segmentation schedules.Methods and meterials:Clonogenic assay was used to evaluate the parameters of cell survival curve of Anip973 cell line(from the radiobiology laboratory of Cancer Hospital(Institute), Peking Union Medical College, Chinese Academy of Medical Sciences)(The irradiation dose points were 0,1,2,4,6,8,10Gy). Cell survival curve was fitted with the linear-quadratic and multi-target/single-hit model; surviving cells count assay was used to drawing Anip973 cell growth curve to calculate the doubling time(number of inoculated cells inl×105); comet assay was used to determine half-time of repairment to irradiation with 5Gy single dose, T1/2 (time points were 0,10,20,30,45,60).Result:When fitted with LQ model,,a was 0.124Gy-1 and β was 0.060Gy-2. When fitted with multi-target/single-hit model, Do was 1.294Gy, Dq was 1.201Gy and SF2 was 0.455, respectively. The cell doubling time of Anip973 cell was 30.64h. The T1/2 was 7.72minConclusion:SF2 of Anip973 was 0.455.Anip973 cell line was moderately radiosensitive.