Objective: To investigate the effect of six degree of freedom (6-DOF) bed combined with cone beam computed tomography (CBCT) in the on-line correction of setup errors in patients with primary rectal cancer. Methods: The clinicopathological data of 17 patients with primary rectal cancer in Department of Radiotherapy, Third Hospital of Peking University from July 2013 to January 2014 were collected. There were 14 males and 3 females, a median age of 65 years. The difference of CBCT and 6-DOF bed combined with CBCT online correction of patients with positioning error were retrospectively analyzed. Results: Before position correction, the first CBCT verification of setup errors in the three translation directions including X (left and right), Y (in and out) and Z (up and down) directions were (0.06±0.25) cm, (0.13±0.40) cm and (-0.28±0.31) cm, respectively. The setup errors of RX (rotation pitch), RY(rolling) and RZ (left and right rotation) directions were (0.62±1.15)°, (-0.19±0.99)°, and (-0.34 ± 0.84)°, respectively . After correction of IGRT combined with six freedom of bed, the setup errors of translation X, Y and Z were (0.01±0.09) cm, (-0.01±0.05) cm and (-0.03±0.08) cm, respectively, and the setup errors of rotation RX, RY and RZ directions were (-0.16±0.40)°, (0.36±0.31)°and (-0.01±0.25)°, respectively. There were significant differences in translation direction (X, Y and Z direction) and rotation direction (Rx, RY and RZ) before and after 6-DOF bed combined with CBCT correction (all P<0.05). In the translation direction, the higher frequency range of Z-direction error value was 0.20-0.79 cm. In the rotation direction, the frequency range of error in Rx direction was 0.20°-2.99°. There was no significant difference between bone mode and gray scale model registration (P>0.05). With the progress of radiotherapy, the setup errors of X, Z, Rx, RY and RZ directions increased except Y direction. Conclusions: In radiotherapy, six freedom bed combined with CBCT is helpful to correct the setup errors of patients with primary rectal cancer. Six freedom bed may be used to correct the setup errors of patients with primary rectal cancer online. Image-guided radiation therapy (IGRT) is recommended for bone pattern registration in patients with rectal cancer.
目的： 探讨六自由度床联合锥形束计算机断层扫描(CBCT)在线纠正原发直肠癌患者摆位误差中的作用。 方法： 收集2013年7月至2014年1月就诊于北京大学第三医院放疗科的17例原发直肠癌患者的临床病理资料。男14例，女3例；中位年龄65岁。回顾性分析CBCT和六自由度床联合CBCT在线校正患者摆位误差的差异。 结果： 首次CBCT获得治疗床的3个平移方向X(左右)、Y(进出)和Z(升降)方向的摆位误差分别为(0.06±0.25)cm、(0.13±0.40)cm和(-0.28±0.31)cm；3个旋转方向RX(旋转俯仰)、RY(滚动)和RZ(左右旋转)方向的摆位误差分别为(0.62±1.15)°、(-0.19±0.99)°和(-0.34±0.84)°。六自由度床联合CBCT校正摆位后，X、Y和Z方向的残余误差分别为(0.01±0.09)cm、(-0.01±0.05)cm和(-0.03±0.08)cm，RX、RY和RZ方向的残余误差分别为(-0.16±0.40)°、(0.36±0.31)°和(-0.01±0.25)°。六自由度床联合CBCT校正前、后比较，平移方向(X、Y和Z方向)和旋转方向(RX、RY和RZ方向)的差异均有统计学意义(均P<0.05)。平移方向中，Z方向误差值出现频率较高的范围为0.20～0.79 cm；旋转方向中，RX方向误差出现较大的频率范围为0.20°～2.99°；骨模式和灰度模配准的摆位误差差异无统计学意义(均P>0.05)；随着放疗进行，摆位误差中除Y方向外，X、Z、RX、RY和RZ方向的摆位误差均增大。 结论： 六自由度床联合CBCT有助于减小原发直肠癌患者放疗的摆位误差，建议采用六自由度床在线校正原发直肠癌放疗的摆位误差，直肠癌患者图像引导放射治疗推荐骨模式配准。.
Keywords: Image-guided; Radiotherapy; Rectal neoplasms; Setup error; Six degrees of freedom bed.