Research On Target Margin Of Non-small Cell Lung Cancer Based On Stereotatic Body Radiation Therapy

To quantitatively analyze interfractional setup errors and intrafractional setup errors of non-small cell lung cancer patients received stereotactic body radiation therapy,and provide a reasonable boundary value for the clinical target area of different lung lobes and improve the accuracy of clinical radiotherapy.A total of 300 patients with non-small cell lung cancer treated with SBRT were selected from Zhejiang Cancer Hosiptal.All patients underwent CBCT image scanning before treatment and 100 patients of them underwent CBCT before and after treatment.For each CBCT scaning the images were corrected and the setup error values were recorded.The setup errors were compared between patients using the Thermoplastic Mask and the Vacuum Cushion system.According to anatomical knowledge,the lungs were divided into upper lobe of left lung,lower lobe of left lung,upper lobe of right lung,middle lobe of right lung,lower lobe of right lung,respectively,and calculation and analysis of different lung lobular's random errors and systematic errors of non-small cell lung cancer patient's setup errors and the best value of external lobe boundary value was calculated according to Van Herk's CTV-PTV expirical formula.The setup errors in the left-right(X axis),inferior-superior(Y axis),Anterior-Posterior direction of the Thermoplastic Mask and the Vacuum Cushion system were(0.22±0.19 vs0.24 ± 0.21)cm,(0.30±0.25vs0.24±0.23)cm,(0.21±0.18 vs 0.25±0.12)cm,respectively.The setup errors of patients show that the systematic error of the upper right lobe in the X direction is 0.08 cm,the maximum of the systematic error in the left lobe is 0.20 cm,the upper left lobe and the upper lobe of the right lung The minimum random error is 0.10 cm and the maximum random error of the left lower lobe is 0.16 cm.The random errors of the left upper lobe in the Y direction are also 0.22 cm and 0.19 cm,respectively.In the Z direction,systematic errors in leaf and right middle lobe is the same to the random errors.Therefore,patients with non-small cell lung cancer treated with SBRT that the values of the margin lobe in the X,Y and Z directions of the left upper lobe were 0.4cm,0.4cm and 0.4cm respectively.The values of the margin lobe in the X,Y and Z directions of the left lower lobe were 0.8cm,0.8cm and 0.5cm respectively.The values of the margin lobe in the X,Y and Z directions of the right upper lobe were 0.4mm,0.4cm and 0.5cm respectively.The values of the margin lobe in the X,Y and Z directions of the right middle lobe were 0.6cm,0.6cm,0.6cm respectively.The values of the margin lobe in the X,Y and Z directions of the right lower lobe were 0.6cm,0.7cm,0.6cm respectively.The setup errors analysis of patients' intractional shows that there are significant differences(P <0.05)in setup errors between the two types of fixation system in the Y axis and the Z axis,but there is no statistical significance in the X axis(P > 0.05).There are differences in the setting errors of different lobes in patients.Therefore,CBCT scans of patients before each treatment can significantly reduce the incidence of setup errors.The clinician uses the extroverted values of different lobes as the reference values for the CTV-PTV extroversion boundary to destroy the tumor cells and at the same time greatly reduce the normal tissue toxicity and improve the cure rate.