Study On The Geometry And Dosimetry Of Four-dimensional Scanning Respiratory Moving Target Imaging

Objectives:To analyze the geometrical and dosimetry effects of breathing motion on 4D imaging.Materials and Methods:1.Using 4D-CT and 4D-CBCT and their reconstruction technology,the specific modules of the QUASAR phantom are scanned in 16 specific breathing modes,and the changes in the volume and centroid position of the specific modules are analyzed under different breathing modes.2.Randomly select 20 patients with irregular breathing motion curves,import the QUASAR phantom,and perform 4D-CT scanning for specific modules again to analyze the influence of irregular breathing motion curves on 4D-CT imaging.3.Randomly select 10 patients with lung tumors who underwent 4D-CT scan,and the target areas were all isolated lung tumor.The u RT-TPOIS treatment planning system（developed by Shanghai United Imaging Medical Technology Co,Ltd.）is used to automatically delineate the target areas and organs at risks of 4D-CT images and free breathing basic phase images（FB-CT）,and confirmed by senior physicians.SBRT plan was designed for 110 sets of CT images on the system,and the volume and dosimetry differences of target areas and organs at risks were statistically analyzed under different modal images.Results:1.The 4D-CT scan results of the QUASAR phantom in 16 specific breathing modes show that the volume change rates of specific modules S1,S2,and C3 are62.42±47.64%,35.95±32.02%,and 32.71±20.31%respectively.while 4D-CBCT is48.59±26.76%,8.80±11.43%and 18.19±9.05%respectively;After statistical analysis,it is found that the volume change rate is positively correlated with the amplitude（P<0.05,Tau＿b>0）,but there is no correlation with frequency（P>0.05）.The 4D-CT scan results of the four amplitude breathing curves show that the 95%reference value ranges of the Y-axis change of the phantom center of mass position are（-2.17mm～2.92mm）,（-3.21mm～4.76mm）,（-5.92mm～10.22mm）,（-9.96mm～15.64mm） respectively.4D-CBCT scan results of the four amplitude respiration curves show that the 95%reference value ranges are（-2.93mm～1.14mm）,（-5.33mm～4.38mm）,（-9.87mm～9.21mm）,（-15.94mm～13.66mm）respectively.2.The results of 4D-CT scanning of the respiratory curve of 20 clinical patients showed that the volume change rate of the specific module was lower in the range of40%to 60%;the statistical analysis showed that the specific module volume outlined on the 4D-CT,MIP and AIP images,There are differences(ITV>V_MIP>V_AIP,P<0.05).3.Compared with the volume of the target area outlined in each phase of 4D-CT,the volume of ITV increased by an average of 20.67±14.17%.At the same time,it was found that the target volume delineated by 50%phase was the smallest（P<0.05）;under the premise of no difference in target dose,the lung and heart doses of the clinical plan based on FB-CT were higher than the plan based on 10 phases;There was no significant difference in the dose of organ-at-risk among the ten phases（P>0.05）,and the average dose of lung at the end of inspiration 0%and 90%phases was slightly lower than other phases.Conclusions:Respiration motion will affect the results of 4D imaging.When 4D imaging technology scans a moving target,There is a correlation between the volume change rate and the amplitude;the geometric shape of the target area will change in different respiratory phases.There is no statistical difference in the dosimetry of the organ at risk between the phases,but they are all lower than the basic phase.