CBCT Clinical Studies Of Setup Errors In Precise Radiotherapy Of Lung Cancer

Objective:In this study, Varian ix accelerator airborne imaging system (On Board Imager OBI) real-time collection of patient CBCT images with planning CT images generated by the system to compare, compare thermoplastic membrane with a fixed vacuum pad positioning technology to reduce errors slightly superior nature, about the time of lung cancer radiotherapy positioning error distribution, verify the accuracy of radiotherapy to reduce the positioning error of precision radiotherapy of lung cancer when the target dose planning target volume and the impact of putting the border to provide reference data.Methods:June2010to July2011in the First Hospital of Shanxi Medical University, Department of Radiation Oncology to accept the three-dimensional conformal or intensity modulated radiotherapy for lung cancer patients, selected20cases for clinical studies. Patients were using body holder and thermal plastic film or a fixed vacuum pad positioned in the PET/CT machine (GE Discovery VCT)-scan to obtain the planning CT image, CT image through the LAN transmission to Varian, Eclipse3D treatment planning system. KV CBCT images for patients with radiotherapy placed in the medical linear accelerator Varian, ix, KV the CBCT system of automatic matching and manual matching, the3D volume image data will be collected by the image processing tools and reference planning CT data right, to get patients to the left and right (LR) on the three directions of the head pin (SI) and anteroposterior (AP) position error, such as the error of three directions<3mm, namely the implementation of the irradiation; if either direction error>3mm, to give the online correction. Three times before the general treatment of the patients underwent KV the CBCT scan after1week. Select the CBCT images obtained in patients1, the target outlined in the planning CT and CBCT images by the same radiation therapy physician, then the TPS automatically calculate the target volume. According to the dose-volume histograms for each patient, CT and CBCT two treatment plans GTV, PTV, lung V20, mean lung dose Dmean and spinal cord the maximum amount. SPSS13.0statistical software for data analysis of all the position error, and calculate the displacement of the center of all patients the mean and standard deviation, Wilcoxon signed rank sum test analysis before and after correction position error differences, but also because of its n>50, The normal approximation method for Z-test, P<0.05was considered statistically significant. Before and after the statistical correction of the error data, two-parameter method to calculate the clinical target volume (CTV) to planning target volume (PTV), putting the border (MPTV).The three-dimensional direction of error (translation error), respectively, with the X, Y, and Z axis represents the body, head and feet, and front and rear direction about. Rotation errors on MPTV still under study, there is no point of view to putting the formula.Results:1.20patients received a total of274KV CBCT scanning, wherein the first scanning (before adjusting)146, a second scan (adjusted)128. In X, Y, Z axis in a three direction error less than or equal to3mm times (%) before the adjustment were49(33.6%),36(24.7%),71(48.6%); after adjustment were123(96.1%),121(94.5%),125(97.6%). In all patients with a total of274times KV CBCT scan, three-dimensional orientation error is less than or equal to5mm times (%) before the adjustment, the adjusted respectively66(45.2%),124(96.8%); the three-dimensional direction error is less than or equal to3mm times (%) before the adjustment, after adjustment for19(13%), respectively120(93.7%).2.20patients received274times before and after the adjustment of KV CBCT scan, in X, Y, Z direction of system error (mean)+random error (standard deviation) before adjustment, respectively (1.16±5.39),(2.82±7.08),(-2.23±4.76) after adjusting for mm, respectively (0.57±1.50)、(1.12±2.39)、(-0.73±1.89) mm. U, V, W direction position error respectively (0.72±1.23),(0.06±1.12),(0.12±0.97) degrees, generally not more than3DEG rotation error.3. Outlined the use of CBCT images than CT outlined PTV volume of the PTV volume received an average of37.3cm3.4. V20lung injury index decreased3.1%on average, the average percentage of23.6%; Dmean average decrease196.6cGy, the average percentage of28.2%, CBCT compared with CT of the spinal cord by the largest average decrease1238.4cGy, the average percentage of31.2%.Conclusions:1. Thermoplastic body membrane immobilization techniques can improve the positioning accuracy, on the left and the right, head and foot and front and rear3directions are vacuum pad fixation technique of positioning error.2. Application of KV CBCT after correction, the direction of three-dimensional position error can basically control in3mm.3. According to the formula of lung cancer in three-dimensional directions of CTV-PTV Margin (MPTV) size respectively:X=6.1mm, Y=10.6mm, Z=7.8mm (before adjustment), X=2.19mm, Y=3.91mm, Z=2.78mm (adjusted).4. The use of CBCT image, can reduce the GTV outside boundary, reduction of normal tissue dose, thereby reducing the normal tissue of radioactive injury incidence.