The Establishment Of IMRT3D Anatomical Dose Reconstruction Mothed And Application Testing

It is known to all that error may occur during the calculation of thetreatment plan, the mechanical of machine or dose characteristics, the changesof the patient positions and anatomical structure, IMRT (Intensity-modulatedRadiation Therapy) might have the deviations between the dose distribution andthe treatment plans. The objective of this work is to verify the dose distributionbefore and during the treatment, using the Three-dimensional dose verificationmethod. EPID (Electronic Portal Imaging Device) were applied inThree-dimensional dose verification to measure the portal imaging data duringthe treatment, restore the dose fluence of the incidence or transmission for everyIMRT field, and reconstruct the three-dimensional dose distribution in patientbody using the backprojection algorithm.In this paper, the research mainly includes：（1） The dosimetrycharacteristics of EPID and its calibration. Through image processing andtransmission gain correction, inspection, calibration dose linearity anddosimetry rate response of EPID, establish its model use for IMRT doseverification.(2)Construct the dosimetry parameter model in DC(DosimetryCheck). Determine the output of the accelerator dosimetry model and theprojection dose reconstruction model of the EPID, by measuring the percentagedepth dose, off-axis dose distribution and the output factor of the differentgathered Radiation Field.(3)Perform the pre-clinical test of the accuracy ofthree-dimensional dose distribution, which is reconstructed by the back-projection algorithm. Process the reconstruction test of the measurement dose,using the solid water phantom, before treatment and during the treatmentrespectively. The results of the reconstruction are compared and the conformityof the planar dose distribution is analyzed by the thimble ionization chamberand the2D detector array measurement method.(4)3D dose reconstructionverification of the clinical IMRT treatments. Using the method ofthree-dimensional dose verification of DC and EPID measurement, to performthe reconstruction verification for the head and neck, chest and abdomen IMRT clinical cases, assess the dose deviation between the target region and the OARs，and analyze how these deviation might affect the clinical treatment plans.Through the background correction, transmission gain correction and theresponse consistency calibration, the result of this work shows that, the testedEPID can meet the requirement of the dosimetry properties during performingthe dosimetry measurement of the Clinical treatment plan. the measurement anddose reconstruction in phantom shows that the average deviation of thereconstructed iso dose compared to ionization chamber measurements were0.34%(pre-treatment reconstruction) and3.91(transit reconstruction). In10phantom IMRT test cases, the average deviation of the iso reconstructed dosecompared to ionization chamber measurements were-1.09(pre-treatmentreconstruction) and1.48%(transit reconstruction). The average deviation of isodose calculated by TPS in10brain IMRT based on CT reconstruction was1.89%, and the deviation were-0.4%and-0.9%in2transited cases. The isodose and PTV calculated by TPS in2prostate IMRT were higher than bothpre-treatment and transit reconstruction. The average dose of the organs at riskcalculated by TPS were higher than pre-treatment and transit reconstruction, andthe passing rate were greater than90%and higher than PTV.The dosimetry reconstruction method and the dosimetry model of thethree-dimensional dose verification system with the EPID is qualified thetherapy safety and reliability as well as the three-dimensional dose verificationworking procedure established by clinical IMRT verification.This research isinnovative because it for the first time in China develop and establish atechnique for penetrate dose measurement and the3D dosimetry reconstructionduring the therapy, and the volume dose of the result can be compared with theTPS plan calculation, this work supply a good basis in evaluating clinical effectsand developing the adaptive radiotherapy.Work remains to be done in eliminating the influence of clinical cure aswell as verifying the computational accuracy of the no uniform tissuecorrelation, to further improve the reliability of three-dimensional doseverification during the therapy.