The Study Of Respiratory Gating On Lung Cancer Radiotherapy

Objective:Respiratory movement has always been an essential factor in the radiotherapy of patients with lung cancer,which significantly affects the location of tumors in radiotherapy.The influence of respiratory movement has to be considered during localization and treatment so as to improve the accuracy of the target volume in radiotherapy.In clinic,the radiotherapy physician expands the safety boundary according to the location of the tumor in different lung lobes on the basis of CTV so as to obtain the planning target volume（PTV）of the tumor,which inevitably increases the dose of normal tissues around the tumor and the risk of the corresponding normal tissue complication.Meanwhile,it may also limit the increase of the radiotherapy dose in the PTV of the tumor.The rational application of respiratory gating technology can significantly lower the amplitude of tumor motion,and reduce the cutoff value of the expansion of the target volume delineation due to respiratory movement,thus lessening the volume of PTV.Especially for patients with lung cancer,the application of respiratory gating can increase the volume of lung tissues,reduce the average dose and the exposure volume on organs at risk,so as to better protect the normal tissues and further increase the dose of target volume.In this study,conventional CT simulation technology by plain scanning and respiratory gating technology were respectively adopted in simulated location of patients.There were two sets of different CT sequences for the same patient.Accordingly,the physicists designed two sets of radiotherapy plans,analyzed and compared the two sets of different radiotherapy plans for each patient,compared the merits and demerits of respiratory gating technology in comparison with conventional CT simulation technology,providing clinical reference for the application of respiratory gating technology in radiotherapy of lung cancer and other tumors in the future.Methods:From June 2018 to May 2019,strict grouping and exclusion criteria had been used.Fifteen patients with lung cancer who were treated at the Shaanxi Provincial Cancer Hospital were selected.The patients were informed of breathing training in advance,and routine preparations before radiotherapy such as modelling were completed.During the simulation,the same patient was respectively simulated by conventional CT simulation and in combination with respiratory gating technology.The two sets of CT sequences were uploaded to the Varian Eclipse planning system.The radiotherapy physician performed the target volume delineation,while the physicist produced the plans,so as to compare volume and dosimetry differences between GTV,ITV and PTV,organs at risk both lungs V5,V20,V30 and mean dose,heart V40 and mean dose,maximum dose of esophagus and spinal cord,total monitor units,target volume evenness index and target volume conformity index of the two sets of plans.Results:Comparing the radiotherapy plans of the 15 patients,（1）the volumes of GTV were（53.3±56.9）VS（52.0±55.4）cm³,P=0.338,the difference was not statistically significant.GTVGating was reduced by（1.4±5.9）cm³ compared with the GTV_FBB volume,and the total volume was decreased by 22.7%.The volumes of ITV were（186.7±136.8）VS（115.2±100.0）cm³,P=0.000,and the difference was statistically significant.ITVGating was reduced by（71.5±41.9）cm³ compared with ITV_FBB volume,and the total volume was decreased by 38.3%.The volumes of PTV were（284.3±186.2）VS（199.6±154.6）cm³,P=0.000,and the difference was statistically significant.PTVGating was reduced by（84.7±40.3）cm³ compared with PTV_FBB volume,and the total volume was decreased by29.8%.（2）The dose D95 values of 95%PTV were（5980.2±44.2）VS（6012.4±31.9）cGy,P<0.05,and the difference was statistically significant.Dmean values were（6141.2±21.3）VS（6160.9±29.1）cGy,P<0.05,and the difference was statistically significant.The differences between Dmin,Dmax,D50,D5,CI,HI were not statistically significant.The volumes included by the 95%isodose curve were（208.9±172.2）VS（201.0±150.7）cm³,and the difference was not statistically significant.The volumes included by the 50%isodose curve were（412.9±235.8）VS（263.3±125.2）cm³,P<0.05 and the difference was statistically significant.The volumes of treated areas were（224.4±174.5）VS（191.6±144.3）cm^3,and the difference was not statistically significant.（3）The volumes of both lungs were（3276.3±1147.3）VS（5037.9±1773.9）cm3,P<0.05.The volume of the lungs was significantly increased under respiratory gating conditions compared with the plain scanning conditions,and the difference was statistically significant.The V5 values of both lungs were（34.7±9.9）VS（27.1±9.8）%,P<0.05.The V20 values of both lungs were（20.8±6.3）VS（15.5±6.0）%,P<0.05.The V30 values of both lungs were（16.5±6.7）VS（11.6±6.1）%,P<0.05.The differences between V5、V20、V30 in the two sets of plans were statistically significant.The MLD values of both lungs were（6147.2±23.4）VS（6160.9±29.1）cGy,and the difference was not statistically significant.（4）The heart Dmean values were（1486.9±1161.8）VS（1137.1±922.3）cGy,P<0.05,and the difference was statistically significant.The heart V40 values were（12.1±11.7）VS（7.8±8.4）%,P<0.05,and the difference was statistically significant.The spinal cord Dmax values were（3516.9±1139.9）VS（3257.3±1135.9）cGy,P<0.05,and the difference was statistically significant.The D1cc values of the spinal cord were（3435.9±1578.2）VS（2896.18±1183.8）cGy,P<0.05,and the difference was statistically significant.The esophagus Dmax values were（3116.4±2583.3）VS（3353.9±2644.1）cGy.The total monitor units were（848.1±322.8）VS（707.7±136.8）MU,and the total monitor units were reduced by 16.6%under respiratory gating conditions.Finally,15 patients were treated with respiratory gating technology for radiotherapy,while 2 patients were changed to normal intensity-modulated radiotherapy due to incompatibility of breathing during radiotherapy.Conclusion:Compared with conventional CT simulation technology,respiratory gating technology can significantly reduce the boundary with the need of expansion of ITV and PTV in radiotherapy,thus reducing the volume of ITV and PTV,increasing the volume of lung tissues,and reducing the dose of the normal tissues within the target volume and the incidence of radiotherapy side effects.Respiratory gating technology is truly effective in the radiotherapy of lung cancer,which can significantly improve the treatment effect of patients.