Application Of Reconstruction Of Three-dismensional Dosimetry Based On EPID And Positioning-error-calibrated CT In IMRT Patients

Electronic portal imaging device(EPID)was initially used to position verification of patients,In recent years,people increasingly high requirements for dose verification,with the rapid development of radiotherapy technology,The rapid development of EPID has been widely used for the dose verification,due to the good performance.A research has been done on the application of dose reconstruction using EPID,including pre-treatment verification and in vivo verification,mainly discuss the three-dismensional dose reconstruction on EPID-based in vivo dosimetry.Considering the effect of the setup error in dose reconstruction,Therefore,in order to get more real dose in patient,EPID should reconstruct on CT by calibration with placement deviation,which have a reference value in clinical treatment.EDose dose reconstruction software was used in the research,the article introduced the EPID data collection process and EDose software operation process.11 cases of tumor patients were used to pretreatment verfication,including naspharyngeal、esophagus and lung cancer,the average rate of gamma pass rate is 96.65%based on EPID,and the y pass rate was verified by the widely used Mapcheck.The average value is 96.27%,the difference between the two is small,verify the validity and feasibility of the dose verification based on EPID.Six patients with head-and-neck and five patients with chest were selected to online three-dimensional dose reconstruction.The human physical model was CT calibrated with the error of orientation.the calibration was mainly based on CBCT Image as a reference image,with plan CT to rigid registration,after registration CT was simulated treatment position of patients.Finally,The EPID reconstructed dose was compared with planning dose,In this paper,EPIDmcCT and TPSpcT were compared,according to the change of ypass rate of reconstructing dose in patients to find the time node of biggest change,which have a significance to adjustment plan at the right time.For nasopharyngeal carcinoma patients,D1CC(1cc volume dose)of the spinalcord was more fluctuating and higher than planned dose.D1 of the brainstem was more stable and the difference between the planned dose is small.V30 of left and right parotid varies greatly,with a maximum increase of 71.35%.After dose reconstruction,the maximum increase in parotid V30 in each patient was 23,20,26,25,30,and 28 times,which provided a basis for the readjustment of the plan.For patients with chest tumors,Dmax of spinalcord change small,The dose of lung and heart compared with the planned dose were higher,especially Vs of lung have an average deviation of 31.48%(P<0.05).In order to improve the quality of patients life,it is important to observe the dose of OAR,and preparing for the next of re-planning,so it is a great significance that EPID-based in vivo dosimetry.