Application Of 4D-CT Combined With Respiratory Gating Technology In Stereotactic Radiotherapy Of Lung Cancer

Objective:The aim of this paper was the evaluation of the application of 4D-CT scan combined with free breathing?FB?,respiratory gating?RG?and active breathing control?ABC?in stereotactic radiotherapy for lung cancer.Dosimetric differences of target volume and organs at risk were analyzed.To explore the clinical application value of 4D-CT combined with respiratory gating in stereotactic radiotherapy for lung cancer.Materials and methods:Twenty-one lung cancer patients?25 lesions?were enrolled in our department from June 2018 to February 2019.All lesions were treated with SBRT.The prescribed dose was 50 Gy in 5 fractions of 10 Gy per day.All patients underwent 4D-CT scan.According to different respiratory phases,the obtained CT data were reconstructed and layered to obtain 10 groups of images:0%-90%.10 groups of images were imaged by average intensity projection to form a full-time image,which was used to simulate ordinary CT images in free breathing mode;30%-70%of the phase images were selected as the respiratory gated images after the average intensity projection fusion;The inhalation 0%phase image simulates the active breathing control state image.The corresponding GTV and PTV were determined on these 3 groups of images,and dosimetry differences of the target volume and organs at risk in Plan-FB,Plan-RG and Plan-ABC based on these three treatment modes were compared.Results:Compared with Plan-ABC,GTV and PTV volume in Plan-FB increased by?18.00±15.33?cm³ and?49.82±38.24?cm³,respectively,and the difference was statistically significant?p=0.031,p=0.014?;compared with Plan-RG,it increased by?10.00±8.67?cm³ and?25.96±17.30?cm³,respectively,and there was no statistical significance.GTV and PTV in Plan-RG increased by?8.00±7.65?cm3 and?23.87±23.24?cm3 compared with Plan-ABC,and there was no statistical significance.There were also no statistical significance between the target dose conformity index?CI?and gradient index?GI?among the three programs.As compared with the Plan-FB,the V₅,V₂₀ and MLD of the lungs in Plan-RG decreased by?5.86±2.62?%,?2.90±1.29?%and?0.66±0.48?Gy,respectively,and the difference was statistically significant?p=0.031,p<0.001,p=0.031?;the V₅,V₂₀ and MLD of the lungs in Plan-ABC decreased by?11.70±4.22?%,?4.64±0.91?%and?1.79±0.46?Gy with statistical significance?p<0.001,p<0.001,p=0.007?.As compared with Plan-RG,the V₅,V₂₀ and MLD of the lungs in Plan-ABC decreased by?5.84±2.27?%,?1.74±0.61?%and?1.13±0.70?Gy,respectively,and the difference was statistically significant?p=0.018,p<0.001,p<0.001?.There were no statistical significance for doses of organs at risk?trachea,proximal bronchial tree,heart,large blood vessels,esophagus,chest wall,spinal cord,brachial plexus and skin?among the three programs.Conclusion:Compared with the common CT technique in free breathing mode,the application of 4D-CT combined with respiratory gating or active respiratory control in lung cancer stereotactic radiotherapy could reduce the target volume,increase the target dose,and protect the normal tissue.In practical clinical applications,4D-CT combined with respiratory gating could be better applied to lung cancer patients with poor lung function or poor compliance.