Study On The Clinical Effect And Mechanism Of Injury By High Single-dose Irradiation

Objective:To reveal and validate the biological mechanism of the model of high single-dose irradiation,we retrospectively analyzed the clinical effect by this method and compared the level of cellular necrosis,apoptosis,DNA damage and the change of cell cycle with different dose in one fraction radiation therapy from cellular or animal experiment.Method:(1)We retrospectively analyzed 40 cases with brain metastatic lesion treated by Cyberknife,whose data means were integrity,in TianJin Tumor Hospital from Aug.1 in 2006 to Aug.1 in 2007.Total brain metastatic lesions were 68, maximum diameter 0.4-7.5cm,median diameter 1.88cm.Some of lesions were treated by whole brain radiation therapy before.All were followed up more than 3-15 months.From these data,we analyzed symptom improving rate,local control rate, survival rate and correlation factor to recurrent focus.(2)We cultivated human pancreatic carcinoma cell line,MIA PaCa-2,and divided into 5 groups:0,2,5,10,17Gy.Cultivated cells were radiated by 6MV-X ray in one fraction with medical processing accelerator.After radiation,we analyzed cellular apoptosis,necrosis and change of cell cycle by flow cytometry,degree of injury of DNA by DNA ladder qualitatively and by comet assay quantitately and cellular morphous by histological technology.(3)We inoculated subcutaneouly human pancreatic carcinoma cell line (MIA PaCa-2)in lateral of right lower extremity of athymic mouse to raise transplantation tumor.While the median diameter of transplantation tumor reached 10mm approximately,animals were randomly divided into 7 groups(8 animals per group)and fixed under conscious condition to be radiated by different dose in one fraction(0GY,2GY,5GY,10GY,17GY,25GY,35GY).Two animals from every group were randomly chosed and executed to gain transplantation tumor for histological chip.Others were kept on to breed for observation of gross tumor volume change,calculation of delayed growth time and delayed growth curve.Results:(1)After the cases with brain metastatic lesion treated by Cyberknife, symptom improving rate,3-month local control rate,treat effective rate,3-month survival rate and 1-year survival rate was respectively 90.00%(36/40),69.12% (53/68),94.12%(64/68),100%(40/40),88.89%(24/27).Among all cases,recurrent focus is 35.00%(14/40)and not correlated to treat mode,whole brain radiation therapy and indifferent dose of radiation therapy.(2)After X-ray radiation, morphology change of human pancreatic carcinoma cell line(MIA PaCa-2)was mainly swelling.This change was direct to dose of radiation therapy especially in low dose group.To follow increase of dose of radiation therapy when dose is less than 10GY,apoptotic necrosis and G₂/M blockage of cell cycle was more obviously,which accorded with traditional radiation biological concept.When dose is more than 10GY, it appeared early and strongly and the peak of apoptotic necrosis was early to G₂/M blockage of cell cycle.The degree of injury of DNA was also dependent on dose of radiation therapy and most obvious in 10GY group.When dose is less than 10GY, DNA ladder was single electrophoresis band;10GY group,it appeared multiple typical ladder band;more than 10GY,vague irregular bands.Oncotic necrosis is mainly style as more than 10 GY in one fraction.(3)With increasing dose per fraction,more than 10 GY in one fraction can show very good biological effect that cellular necrosis is from apoptosis to necrosis in histology,cutaneous reaction on the surface of animal neoplasma that is main moist yellow effusion was more and more severe,the effect of tumor delayed growth was obvious related to dosage.When dosage is less than 10GY,all animals showed similar effect that their grow rate first decreased and then increase to more than before.Other groups showed that tumor volume was less.The difference in two similar groups has statistical significance. Tumor delayed growth time(tumor volume decrease first and then re-increase to original volume)in 10,17,25,35 GY group was respectively 3 weeks,6 weeks, more.Conclusions:The clinical effect of the model of high single-dose irradiation was very good.Cell injury and DNA injury was dependent on dose of radiation therapy and most obvious in 10GY group.Oncotic necrosis is mainly style as more than 10 GY in one fraction.The effect of tumor delayed growth was obvious direct related to dosage after transplantation tumor was radiation.10 GY group showed a boundary effect.25 Gy is recommended as a clinical curative dose,because it had best biological effect.On account of its truth,cyberknife become best executive for the model of high single-dose irradiation.