Dosimetric Study And Application Of Respiratory Gating In Stereotactic Body Radiation Therapy For Early-stage Non-small Cell Lung Cancer

Objective:To investigate the application of respiratory gating in stereotactic body radiation therapy(SBRT)for early-stage non-small cell lung cancer(NSCLC).To design SBRT plans for early-stage NSCLC patients with prospective gating,retrospective gating,motion enveloped method and conventional population margin-based 3D-CT,respectively,and to compare the differences in dosimetric and radiobiological parameters of target areas and organs at risk between the four plans,as well as to evaluate the short-term efficacy and acute toxic side effects of patients applying retrospective gated SBRT,so as to provide ideas and references for clinical early-stage NSCLC SBRT treatment.Methods:Twenty-one patients with pathologically confirmed early-stage NSCLC were selected.3D-CT,4D-CT cine mode and end-expiratory prospective respiratory-triggered axial-R mode scans under free breathing were performed for each patient,respectively.The scanned images were transmitted to the Varian treatment planning system to delineate target areas and organs at risk as follows.(1)PTVpro: GTV was delineated layer by layer on the end-expiratory gated scan CT images.For end-expiratory plateau images using respiratory-triggered axial scans,the respiratory motion was considered to be zero.The ITV was uniformly expanded by 8 mm in all directions to generate the PTV.(2)PTV30-70:GTV is delineated layer by layer on 10-phase 4D-CT images.Generate the average intensity projection(AIP)image of 30%-70% phase,and superimpose the GTV fusion of 30%-70% phase on its AIP image to generate ITV.The ITV was uniformly expandedby 8 mm in all directions to generate the PTV.(3)PTVall: Generate the AIP image of10-phase CT images,and superimpose the 10-phase GTV fusion on its AIP images to generate ITV.The ITV was uniformly expanded by 8 mm in all directions to generate the PTV.(4)PTV3D: The GTV was delineated layer by layer on the 3D-CT image.The GTV was expanded 1.5 cm in the direction of cranial-caudal,and 1 cm in the direction of ventral-dorsal and left-right to generate the PTV.With FFF VMAT SBRT technology under the same condition,four corresponding plans,prospective gating(Planpro),30%-70% temporal retrospective gating(Plan30-70),motion enveloped method(Planall)and conventional population margin-based 3D-CT(Plan3D)were designed,respectively.Prescription dose: PTV 60 Gy/8F,7.5 Gy/F,5F/W.The difference of dosimetric and radiobiological parameters in target areas and organs at risk of the four groups was statistically analyzed.All patients were treated with retrospective gated SBRT.Short-term efficacy was evaluated one month after radiotherapy and acute toxic effects were counted in the third month.Results:1.Among the three groups plans adopting respiratory motion management technology,except target CI,HI and TCP,there were statistically significant differences in other parameters(P<0.05).Pairwise comparisons showed that the PTV,the V5,V10,V20,V30,V14.4,MLD of both ipsilateral lung and bilateral lung,bilateral lung NTCP,heart Dmax and esophagus NTCP of Planpro were all lower than those of PTV30-70,and the difference was statistically significant(P<0.05),but there was no statistically significant difference in esophageal Dmax,spinal cord Dmax and proximal bronchial tree Dmax(P>0.05).The PTV,ipsilateral lung V5,the V10,V20,V14.4,MLD of both ipsilateral lung and bilateral lung,spinal cord Dmax and proximal bronchial tree Dmax of PTV30-70 were lower than those of Planall,and the difference was statistically significant(P<0.05).but there was no statistically significant difference in theipsilateral V30,bilateral lung V5,V30,NTCP,heart Dmax,esophageal Dmax and esophageal NTCP(P>0.05).All parameters of Planpro were lower than those of Planall,and the difference was statistically significant(P<0.05).2.Between Planall and Plan3 D of a complete respiratory cycle,in addition to CI,HI,and spinal cord Dmax,the PTV,TCP,the V5,V10,V20,V30,V14.4,MLD of both ipsilateral lung and bilateral lung,bilateral lung NTCP,heart Dmax,esophageal Dmax,esophageal NTCP and proximal bronchial tree Dmax of Planall were lower than those of Plan3 D,and the difference was statistically significant(P<0.05).3.Among the 21 patients,0(0.00%)patient was in complete remission,14(66.67%)patients were in partial remission,7(33.33%)patients had stable disease,and 0(0.00%)patient had progressive disease.No acute radiation injury of grade 3 or higher was observed in all patients,including 4 cases(19.05%)of grade 1 radiation pneumonia and 1 case(4.76%)of grade 2 radiation pneumonia;1 case(4.76%)of grade 1 radiation esophagitis;4 cases(19.05%)of grade 1 radiation myelosuppression and 3 cases(14.29%)of grade 2 radiation myelosuppression.Conclusions:1.Conventional population margin-based 3D-CT overestimates the target area PTV and TCP and increases the irradiated dose to the lung,heart,esophagus and proximal bronchial tree.2.Among the three respiratory motion management technology plans,compared with the motion enveloped method,the retrospective gating and prospective gating techniques both reduce the PTV without losing the target CI,HI and TCP.Retrospective gating reduces the irradiated dose to the lung,spinal cord and proximal bronchial tree,and obtains good short-term efficacy and safety in clinical practice.While the irradiated dose to the lung,heart,esophagus,spinal cord and proximal bronchial tree are all reduced in prospective gating,and the lung dose isfurther reduced compared with retrospective gating,which could better protect the surrounding normal tissues and organs.