胸部肿瘤常规放疗摆位偏差的测量与分析

目的　确定胸部肿瘤常规放射治疗时的摆位偏差。方法　使用电子射野影像装置(EPID)对 2 1例胸部肿瘤病人常规放射治疗时所拍摄的 40 8幅射野图像 ,与计划系统生成的标准射野数字重建 (DRR)图像进行了比较 ,并对病人摆位的横向 (RL)和纵向 (SI)及前后 (AP)轴旋转角度的偏差进行了测量。结果　没有采用任何固定装置治疗时 ,RL和SI方向摆位的平均平移偏差分别为(0 7± 3 1 )mm和 (1 5± 4 1 )mm ;平均旋转偏差为 (0 3± 2 4)°。当使用体膜固定治疗时 ,RL和SI方向摆位的平均平移偏差分别为 (0 5± 2 4)mm和 (0 8± 2 7)mm ;平均旋转偏差为 (0 2± 1 6)°。结论　胸部肿瘤放射治疗时采用体部固定装置可降低摆位偏差。SI方向的摆位偏差大于RL方向的摆位偏差。摆位偏差的主要来源是随机误差

Measurement and analysis of the thoracic patient setup deviations in routine radiotherapy

Objective To determine the magnitude of the setup deviations of the thoracic patients in routine radiotherapy. Methods Altogether 408 films for 21 thoracic patients were recorded using the electronic portal imaging device (EPID), and comparison with reference CT simulator digitally-reconstructed radiograph (DRR) for anterior-posterior fields was performed.The deviation of setup for 21 patients in the left-right (RL), superior-inferior(SI)directions and rotation about the anterior-posterior (AP) axis were measured and analyzed. Results Without immobilization device, the mean translational and rotational setup deviations were (0. 7±3. 1) mm and (1.5±4. 1) mm in the RL and SI directions, respectively, and (0. 3±2. 4)° about AP axis.With immobilization device, the mean translational and rotational setup deviations were (0.5±2.4) mm and (0.8±2. 7) mm in the RL and SI directions respectively, and (0.2±1.6)° about AP axis. Conclusion The setup deviations in thoracic patients, irradiation may be reduced with the use of the immobilization device.The setup deviation in the SI direction is greater than that in the RL direction.The setup deviations are mainly random errors.