OBI系统在放射治疗摆位中的临床应用

目的：放射治疗中患者的摆位误差是影响精确治疗的关键因素之一。与常规外照射相比，适形调强放射治疗对摆位精度的要求进一步提高。作者使用Varian Trilogy直线加速器的OBI系统对不同部位肿瘤的进行摆位误差研究，探讨适合我科的PTV形成方法。方法：对我科适形调强放疗的207例患者进行研究，头颈部患者27例、胸部患者47例、腹部患者20例、盆腔患者113例。所有患者均采用热塑料体（面）模固定，每周行1次CBCT图像采集或每周行2～3次OBI图像采集，将采集的患者DR图像或CBCT图像与计划系统所生成的DRR图像或CT图像的进行比较，分析摆位误差，并且计算不同部位肿瘤的PTV大小。结果：207例患者共进行位置验证698人次，其中头颈部患者104人次、胸部患者156人次、腹部患者36人次、盆腔患者370人次，将系统误差∑和随机误差σ分开研究。头颈部肿瘤前后、头脚、左右方向误差为：0．16±0．22cm、0．18±0．24cm、0．17±0．29cm；胸部肿瘤前后、头脚、左右方向误差为：0．39±0．47cm、0．41±0．55cm、0．24±0．30cm；腹部肿瘤前后、头脚、左右方向误差为：0．30±0．39cm、0．35±0．46cm、0．26＋0．32cm；盆腔肿瘤前后、头脚、左右方向误差为：0．27＋0．38cm、0．34＋0．44cm、0．20±0．28cm。头颈部任一方向大于0．3cm的值是30．8％，胸、腹部及盆腔任一方向误差大于0．5cm的值分别是：55．8％、38．9％、14．30／00根~Stroom的2∑＋0．70公式计算MargtnX小，头颈部肿瘤前后、头脚、左右方向Margin为：0．5cm、0．5cm、0．5cm；胸部肿瘤前后、头脚、左右方向Margin为：1．1cm、1．2cm、0．7cm；腹部肿瘤前后、头脚、左右方向Margin为：0．9cm、1．0cm、0．7cm；盆腔肿瘤前后、头脚、左右方向Margin为：0．8cm、1．0cm、0．6cm。结论：使用OBI系统在线或离线指导摆位误差的修正是非

OBI Clinical Application In setup Error

Objective：In radiotherapy, setup errors in positioning the patients influence the size of safety margin and thereby also the size of irradiation field and toxicity of radiotherapy. Compared with traditional radiotherapy, higher positioning precision is required in three-dimensional radiation therapy （3DCRT） and intensity modulated radiation therapy （IMRT）. In this study, we investigated the setup errors in the treatment of different regions by Varian＇s OBI system and defined margins for the definition of planning target volume in our own institute. Methods：The positioning data of 207 patients treated with 3DCRT and IMRT for different regions （27 patients in head and neck, 47 patients in thorax, 20 patients in abdomen and 113 patients in pelvis） were analyzed. All patients were immobilized with thermoplastic mask. Cone beam CT images were taken once a week and on-board kilovoltage images were collected twice or third a week. An anatomy template consisting of contours of relevant bony structures on DRR and simulated CT images were drawn and compared to obtain the positioning data. For all three directions （x, y, z）, random and systematic set-up deviations were measured. Margins for planning target volume were defined accounting for systematic and random set-up uncertainties. Results：698 images （104 images in head and neck, 156 images in thorax, 36 images in abdomen and 370 images in pelvis） were obtained from the treatment of 207 patients. For each patient, the systematic and random errors for the different directions were measured separately. Random setup errors in head and neck replacement repeatability were within 0.40 cm in every direction, in thorax irradiation were within 0.39±0.47 cm, 0.41±0.55 cm, and 0.24±0.30 cm for the lateral, anterior-posterior, and superior-inferior directions respectively. Random setup errors in abdomen showed 0.30±0.39 cm,0.35±0.46 cm ,and 0.26±0.32 cm along the left-right, cranio-caudal and anterior-posterior direction respectively, in pelvis were