用锥形束CT图像测量放疗摆位误差

Setup errors with image guided radiotherapy technique

目的探讨图像引导放疗(IGRT)系统的临床摆位误差。方法应用医科达SynergyTM系统治疗51例,其中头颈部肿瘤19例,胸部肿瘤25例,腹、盆部肿瘤7例。每次照射前获取X线容积图像(XVI)即锥形束断层扫描(CBCT),将CBCT图像和计划CT图像及其靶中心匹配,获得靶中心x、y、z方向的误差,分析误差及其分布规律。结果CBCT图像对比度好,临床上能清楚显示肿瘤大小、位置及其和周围的关系。51例每次治疗开始前的CBCT共955次,分别分析头颈部、胸部及腹、盆部摆位误差,均呈正态分布。系统误差(均数)±随机误差(标准差)在x、y、z方向分别为头颈部(- 0.3±1.5)、(-0.3±1.6)、(0±1.3)mm,胸部(-0.6±2.9)、(-0.2±5.6)、(0.7±3.2)mm,腹、盆部(-0.8±2.1)、(-0.3±5.9)、(0.1±2.6)mm。结论通过CBCT测量治疗前摆位误差并实时调整摆位误差,可大大提高患者摆位精度,同时为正确设定计划靶体积(PTV)提供了依据。

Objective This work was to investigate the setup errors of image-guided-radiotherapy （IGRT） . Methods From April 2006 to August 2006, 51 patients were treated with the newly installed Elekta SynergyTM system, among whom there were 19 head and neck tumors, 25 thoracic tumors and 7 abdomino-pelvic tumors. All patients had received kilovoltage cone beam computed tomography （kv-CBCT） before radiotherapy was delivered. The acquired X-ray volumetric images （XVI） were co-registered with planning CT and errors of isocenter positions on x, y, z axes were obtained and analyzed. Results The acquired CBCT images had high quality clearly showing soft tissue organs, tumor size , location and the surrounding structures. All 51 patients received CBCT scan at each treatment fraction before radiation delivery. A total of 955 CBCT scans were obtained. Setup errors in the head and neck, chest and abdominopelvis all gave normal distributions. The systemic ± random errors on x, y, z directions were （ - 0.3 ± 1.5 ） mm, （ -0.3 ±1.6） mm,（0 ±1.3） mm for the head and neck;（ -0.6 ±2.9） mm,（ -0.2 ±5.6） mm,（0.7 ±3.2） mm for the chest; （ -0.8 ±2.1） mm,（ -0.3 ±5.9） mm,（0.1 ±2.6） mm for the abdominopelvis, respectively. Conclusion Measurement of setup error before radiation delivery using kV-CBCT scan combined with on-line correction could greatly improve the patient setup precision and may guide optimal designing.