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目的利用在线高能X线计算机体层摄影术(MVCT)重建两组共45例调强放疗患者的三维图像,研究头颈部与前列腺肿瘤患者的治疗摆位在未经修正情况下的体位和靶区位置偏差,及其对照射剂量分布的影响,探索MVCT图像引导放疗的临床应用方法与意义。方法对实施切层调强放疗患者的计划分布分别以电离室和剂量胶片方法进行体模验证测量,在验证合格前提下用在线MVCT图像与模拟定位的CT图像进行三维融合比较,测量两组患者体位和靶区中心点的偏差,分析两组摆位的系统误差与随机误差。以测量的体位和靶区位移偏差值模拟体位偏差条件,比较模拟条件下测量得到的体模剂量分布与计划剂量分布和正常摆位时的剂量分布差别。结果头颈部和前列腺肿瘤治疗摆位未经修正时靶区的三维位移偏差值分别为(-3.0±2.8)、(-5.4±2.3)、(2.1±2.4)mm和(3.2±2.5)(、-6.4±5.3)、(8.7±3.6)mm。上述位移偏差条件下体模测量的头颈和前列腺照射剂量分布与计划剂量分布的误差分别为8.2%和6.9%。结论在线HVCT能精确快速测量患者体位和靶区位置空间误差,为修正摆位提供准确依据。未经修正时靶区位移误差导致的剂量分布误差可能超出临床允许范围,调强放疗应以在线图像引导验证基础上进行才能保证剂量分布精度。
Objective To reconstruct three-dimensional images of 45 patients with IMRT in two groups by on-line high-energy X-ray computed tomography (MVCT) and study the position and target of treatment placement of patients with head and neck and prostate cancer without modification Region location deviation, and its impact on the dose distribution of radiation to explore the MVCT image guided radiotherapy clinical application methods and significance. Methods The planned distribution of patients undergoing IMRT was measured by phantom with ionization chamber and dose film respectively. The CT images of on-line MVCT images and simulated images were compared and three-dimensional fusion was performed on the premise of verification. Two groups of patients Body position and target center of the deviation, analysis of the two sets of systematic errors and random errors. The body position deviation conditions were simulated by the measured body position and the displacement deviation of the target area. The differences between the dose distribution of the phantom and the dose distribution under the normal condition were compared under simulated conditions. Results The displacement of the target in the head and neck and prostate tumor setup were (-3.0 ± 2.8), (-5.4 ± 2.3), (2.1 ± 2.4) mm and (3.2 ± 2.5) mm , -6.4 ± 5.3), (8.7 ± 3.6) mm. The errors of dose distribution and planned dose distribution of head-neck and prostate irradiation measured by phantom were 8.2% and 6.9% respectively under the above displacement deviation conditions. Conclusions The online HVCT can accurately and quickly measure the space error of the position of the patient and the position of target and provide an accurate basis for the correction of the position. The error of dose distribution caused by the displacement error of the target area without correction may exceed the clinical allowable range. The intensity-modulated radiotherapy should be based on the online image guidance to ensure the dose distribution accuracy.