The Application Of CBCT Guided Radiation Therapy For Thoracic Carcinoma

Part One Comparative evaluation of image registration methods with different interest regions in lung cancer radiotherapyObjective: To evaluation the accuracy of different methods of CBCT image registration used in image-guided radiotherapy,and provided reasonable guidance for clinic application.Methods: 53 patients with thoracic carcinoma were collected,including34 central and 19 peripheral lesions.Varian-IX linear accelerator OBI system was used to acquire CBCT scans in three-dimensional conformal radiotherapy before delivery.We registered with different auto match region(body/ target/vertebrae/ ipsilateral structure)and manual registration,and the position deviation and the time consumption were compared.Results: The position deviation were X axis(mm): 0.226±2.900,0.623±3.295,0.453±2.866,0.000±3.322,0.377±2.669;Y axis(mm): 0.396±7.292,0.208±5.055,0.094±5.838,0.491±6.116,0.094±5.274;Z axis(mm):1.981±2.678,1.830±2.847,1.302±2.334,2.000±2.908,1.264± 2.543,respectively.The difference of X,Y and Z axis was not significant.The time consumption(s)was 3.651±0.867,1.144±0.129,1.226±0.126,2.081± 0.427,179.491±71.975.The differences were significant.After excluded the setup errors,the position deviation were X axis(mm):0.002±.070,0.018±.133,0.023±.148,0.010±.073;Y axis(mm):-0.012±.169,-0.028±.213,-0.047±.309,-0.018±.193;Z axis(mm): 0.023±.128,-0.010±.238,-0.075±.137,-0.030±.175,respectively.The difference of Z axis was significant.Pairwise comparison showed that there was a statistical difference between the registration vertebral group and other groups.Conclusions: Registration time is significantly different.The more factor is considerd,the more time is needed.In clinical,we suggested manualadjusted after registering ipsilateral or whole structure.Part Two Analysis of setup errors and its impact on dosimetric distribution for thoracic carcinoma radiotherapy with conebeam CT-based image guidanceObjective: To study the role of kilovolt cone beam CT(CBCT)on the geometrical accuracy of three-dimensional conformal radiotherapy(3DCRT)and intensity modulated radiotherapy(IMRT)and to analyze the effect of the setup error on the dosimetric distribution of targets and peripheral organs at risk for thoracic carcinoma.Methods: 30 patients with thoracic carcinoma were collected.Varian-IX linear accelerator on-board imaging system was used to acquire CBCT scans in three-dimensional conformal radiotherapy or intensity modulated radiation therapy before delivery.The right-left(x),superior-inferior(y),anteriorposterior(z)setup errors of patients can be obtained from the tomography images automatically restructured by the system.And then CMS treatment planning system was used to analyze the impact of setup errors on dosimetric distribution of targets and peripheral organs at risk if the isocenter was replaced by the actual location which obtained from the CBCT scan.Results: The setup error were(-0.20±2.84),(-1.09±5.40),(-2.61±2.08)mm respectively and the absolute maximum was 13 mm,21mm,8mm respectively according to 270 CBCT scans on x,y,z directions.Within 5mm of which accounted for 97.8%,73%,92.6% respectively.The difference of PTV D95%,PTV Dmean,GTV D95% and GTV Dmean was significant if setup errors more than 5mm in any direction(P=0.000).Conclusions: Setup errors of this group mostly within 5mm.It was more obvious in the y directions.There was significantly difference if setup errors more than 5mm in any direction.Part Three Analysis of setup errors and margin for thoracic carcinoma radiotherapy with cone-beam CT-based image guidanceObjective: To study the role of KV CBCT on the geometrical accuracy of three-dimensional radiotherapy and to evaluate the margin of targets and peripheral OAR for thoracic carcinoma.Methods: 34 patients with thoracic carcinoma were collected.Varian-IX linear accelerator OBI system was used to acquire CBCT scans in three-dimensional conformal radiotherapy before delivery.The left-right(x),superior-inferior(y),anterior-posterior(z)setup errors of patients can be obtained from the tomography images automatically restructured by the system.Results: According to 279 CBCT scans the systemic ±random error on x,y,z directions were(2.41±2.18)mm,(4.27±3.60)mm,(2.71±1.77)mm and(-0.16± 3.25)mm,(-1.36±5.43)mm,(-2.43±2.14)mm respectively if we consider the direction of setup errors.The margins of targets were calculated as2.68 mm,7.19 mm and 7.57 mm respectively.PRV margin were 0.21±1.34、1.76±3.59、3.16±3.78 mm respectively。Conclusions: Setup errors are unavoidable in thoracic carcinoma irradiation.we suggested a PTV margin of 2.68 mm,7.19 mm and 7.57 mm in the left-right,superior-inferior and anterior-posterior directions respectively in our department.PRV margin were determined according to the specific situation.Part Four Factors influencing interfractional setup errors in thoracic carcinoma radiotherapy with cone-beam CT-based image guidanceObjective: To investigate the influence of tumor size,location,and patient characteristics on the interfractional setup errors in thoracic carcinoma radiotherapy with cone-beam CT-based image guidance.Methods: 59 patients with thoracic carcinoma were collected.Varian-IX linear accelerator on-board imaging system was used to acquire CBCT scans in three-dimensional conformal radiotherapy or intensity modulated radiation therapy before delivery.The right-left(x),superior-inferior(y),anteriorposterior(z)setup errors of patients can be obtained from the tomography images automatically restructured by the system.The degree of interfractional setup errors(3D errors)was measured by isocenter translation vector of magnitude(X2+Y2+Z2)1/2.Statistical correlations of these shifts with the characteristics of the patient(sex,age,height,weight,body mass index,volume of the left lung,volume of the right lung)and the tumor(diameter,volume,lung carcinoma vs esophageal carcinoma,location in upper vs lower,central vs peripheral,right vs left)were determined.Results: Overall,200 inerfractional shifts were measured on the 59 patients.On 12 occasions(6%),X-shifts larger than 5mm were observed.The setup error larger than 5mm in Y-shifts,Z-shifts,and 3D shifts were 29(14.5),7(3.5%),and 93(46.5%)respectively.In single variation models we found that sex,height,BMI,volume of the left lung,volume of the right lung,tumor location,were significantly associated with the 3D shifts.In the multivariable regression model analysis indicated height(P=0.009),the volume of right lung(P=0.014),and the location of the tumor(upper vs lower)(P=0.000)are predictors for interfractional shifs for thoracic carcinoma radiotherapy.Conclusions: Patients have their inherent shifts in thoracic carcinoma radiotherapy.Sex,height,BMI,volume of the left lung,volume of the right lung,tumor location were significantly associated with the 3D shifts.Male,thinner,small BMI,and bigger lung volume have little setup errors.