Study Of Volumetric Modulated Arc Therapy And Conventional Intensity Modulated Radiation Therapy On Acute Radiation Induced Lung Injury

Objective:1.Dosimetric differences in thoracic tumor target volume and organs at risk（OARs）were compared between volumetric modulated arc therapy（VMAT）and intensity modulated radiation therapy（IMRT）,and a feasibility of ArcCHECK three-dimensional dose verification system in the validation of intensity modulated plan is studied.It can provide a reference for individualized radiotherapy and reduce the incidence of radiation lung injury（RILI）.2.To investigate the correlation between the lung dose volume parameters and the incidence of acute RILI in patients with thoracic tumor after intensity modulated radiation therapy.Combined with patient related clinical factors,we provide relevant evidence for clinical individualized radiotherapy and early intervention for possible RILI,in order to reduce the incidence of RILI and improve the quality of life of patients.Methods:1.From August 2016 to April 2017,thirty cases of non small cell lung cancer（NSCLC）and thirty-two cases of esophageal cancer were collected from the Radiotherapy Department of Affiliated Hospital of Qinghai University.The VMAT and IMRT plans were designed for each patient,and the differences in target dose distribution,OARs dose volume parameters and monitor unit（MU）were compared.In the treatment plan system（TPS）,the plan was transplanted to the ArcCHECK phantom to recalculate the dose,and placed the phantom to the accelerator.According to the plan of the patient,we evaluated the gamma pass rate of each patient（standard:3mm,3%,threshold 10%）.The 3DVH software was used to compare the deviation of dose volume parameters in the target and lung between3DVH recalculation and TPS calculation.2.From July 2017 to January 2018,seventy-five cases of thoracic tumor were collected from the Radiotherapy Department of Affiliated Hospital of Qinghai University.The incidence of acute RILI was observed within three months from radiotherapy,and the acute RILI grading standard of RTOG was used for classification.The correlation between acute RILI incidence and lung dose volume parameters was evaluated.The dose volume parameters of lung were used to assess the association with the incidence of acute RILI,and the factors related to the occurrence of acute RILI were analyzed according to the treatment,age,sex,nationality,smoking,drinking,tumor type,stage,pathological type,COPD and KPS score.Results:1.The homogeneity index（HI）and conformal index（CI）of VMAT plan was better than that of IMRT plan,and the MU decreased significantly.There was no statistically significant difference in the mean lung dose between the two groups（P>0.05）.The V₂₀,V₃₀ and V₄₀ of VMAT were superior to those of IMRT,the difference was statistically significant（P<0.05）,while V₅ and V₁₀ were worse than IMRT,the difference was statistically significant（P<0.05）.There was no statistical difference between the two groups of Dmax of the spinal cord in NSCLC（P>0.05）.The Dmax of the spinal cord of VMAT in esophageal cancer was lower than that of IMRT,and the difference was statistically significant（P=0.002）.In the 3mm,3%standard of gamma analysis,all planned gamma passing rates were more than 95%.Compared with the dose volume parameters of the calculated results of 3DVH and TPS,the deviations of D_2%,D_98%,D_50%and D_mean in all the target areas of PTV were within 3%.In the IMRT plan of NSCLC,there were two patients with lung V₃₀ and V₄₀deviations>5%,the maximum were 6.37%and 5.49%,respectively.In the VMAT plan of NSCLC,there was one patient with lung V₃₀ and V₄₀ deviations>5%,the maximum were-5.09%and-6.66%,respectively.In the IMRT plan of esophageal cancer,there were two patients with lung V₃₀ and V₄₀ deviations>5%,the maximum were 5.69%and 7.36%,respectively.In the VMAT plan of esophageal cancer,there ware two patients with lung V₃₀ and V₄₀ deviations>5%,the maximum were-5.79%and-6.76%,respectively.The dose volume deviations of lung in all the other plans ware less than 5%.2.The single factor chi-square test,MLD<13Gy,V₅<58%,V₂₀<25%,V₃₀<13%and without COPD,the incidence of acute RILI was significantly decreased,and the difference was statistically significant（P<0.05）,and the other lung dose volume parameters and clinical factors were not significantly related to acute RILI（P>0.05）.Logistic regression analysis showed that MLD,V20 and COPD were significantly related to the occurrence of acute RILI,and V₅ and V₃₀ were confounding factors.Conclusion:1.In thoracic tumor radiotherapy,VMAT plan has the better HI and CI of target volume which will help to increase the gain ratio of tumor radiotherapy,and reduce the volume of middle and high dose area of lung and MU.Compared with IMRT,it has more advantages.In some cases,VMAT may help reduce the occurrence of RILI.2.ArcCHECK combined with 3DVH can verify the dose distribution and compare the dose volume histogram（DVH）of clinical anatomy.This helps to improve the safety of clinical radiotherapy and reduce the incidence of RILI in the thoracic tumor radiotherapy.3.MLD,V20 and COPD were the risk factors for the occurrence of acute RILI after intensive radiotherapy of thoracic tumor.4.At high altitude,especially in patients with COPD,the volume of the lung dose should be as small as possible and the control needs to be stricter.