探讨在使用六自由度床的情况下，接受盆腔放疗的直肠癌患者的固定方式选择。

通过对北医三院放射治疗科2015年11月1日至2016年3月25日行盆腔放射治疗的27例直肠癌患者整个疗程中的六自由度床校正摆位误差的分析，比较低温热塑膜和真空垫的固定效果。热塑膜体网入组17例患者（组1），负压真空垫组入组10例患者（组2）。

热塑膜体网组在六自由度床的校正前后的摆位误差值在X、Y、Z、RX、RY及RZ方向差异均有统计学意义（t=0.732，1.408，-2.335，5.237，-3.154，-1.130；均P＜0.05）；而负压真空垫组在六自由度床的校正前后仅在Z、RX及RY方向差异有统计学意义（t=-13.128，9.945，-5.993；均P＜0.05），X、Y及RZ方向差异无统计学意义（t=1.706，6.508，-5.34；均P＞0.05）；说明在患者治疗期间，热塑膜体网组六自由度床有较好的校正效果。两组在未经六自由度床校正前的摆位误差仅在RY（t=2.226，P=0.027）及RZ（t=-2.686，P=0.008）方向上差异有统计学意义，其余方向差异均无统计学意义（均P＞0.05），且负压真空垫固定组在RZ方向上的摆位误差小于热塑膜体网组；说明负压真空垫在患者身体长轴方向上的固定效果较理想。经过六自由度床校正后，两组在患者治疗后的摆位误差比较在Z方向上差异有统计学意义（t=3.267，P=0.001），其余方向差异均无统计学意义（均P＞0.05），且热塑膜体网组在Z方向上的摆位误差较小；说明在经过六自由度床校正后，热塑膜体网组在Z方向上有较好的固定效果。未经六自由度床校正时，公式计算的组1的PTV外放边界：X为0.33 cm、Y为0.61 cm及Z为0.90 cm；组2的PTV外放边界：X为0.39 cm、Y为0.42 cm及Z为0.99 cm。经过六自由度床校正后组1的PTV外放边界：X为0.09 cm、Y为0.06 cm及Z为0.08 cm；组2的PTV外放边界：X为0.12 cm、Y为0.2 cm及Z为0.57 cm，说明热塑膜体网组有较好的固定效果。

本研究中，接受盆腔放射治疗的直肠癌患者在使用六自由度床校正摆位误差时，相对于负压真空垫，更推荐使用热塑膜体网固定。

To explore the choice of fixation options for rectal cancer patients receiving pelvic radiotherapy under the condition of using a 6-DOF (six-degree-of-freedom) bed.

Twenty-seven patients with rectal cancer who underwent pelvic radiotherapy in our department from November 1, 2015, to March 25, 2016, were analyzed of the setup errors to evaluate the fixation effect of low-temperature thermoplastic film and vacuum pad.

There were significant differences in X, Y, Z, RX, RY, and RZ in the heat-shrinkable film mesh group before and after the 6-DOF bed correction (t=0.732, 1.408, -2.335, 5.237, -3.154, -1.130; P＜0.05). There were significant differences in Z, RX, and RY directions in the negative pressure vacuum pad group before and after the correction 6-DOF bed (t=-13.128, 9.945, -5.993; P＜0.05), but there was no significant difference in X, Y and RZ directions (t=1.706, 6.508, -5.34; P＞0.05). The results showed that during the treatment, the thermoplastic membrane mesh group had a proper correction effect. Before the 6-DOF bed correction, the setup errors of the two groups were statistically different only in the direction of RY (t=2.226, P=0.027) and RZ (t=-2.686, P=0.008), and there was no significant difference in other directions (P＞0.05). Moreover, the setup errors in the RZ direction of the vacuum pad fixation group were smaller than that of the thermoplastic film body mesh group, indicating that the vacuum pad fixation effect in the patient's body's long axis is ideal. After 6-DOF bed correction, the setup errors of the two groups were statistically different only in the Z direction (t=3.267, P=0.001), but there was no significant difference in other directions (P＞0.05). Moreover, the thermoplastic film mesh group's setup errors in the Z direction were smaller, which indicated that the thermoplastic film mesh group had better fixation efficiency in Z direction after a 6-DOF bed correction. Before a 6-DOF bed correction, the PTV extension boundary of X, Y, and Z of group 1 was 0.33 cm, 0.61 cm, and 0.90 cm, respectively; The PTV extension boundary of X, Y, and Z of group 2 was 0.39 cm, 0.42 cm, and 0.99 cm, respectively. After a 6-DOF bed correction, the PTV extension boundary of X, Y, and Z of group 1 was 0.09 cm, 0.06 cm, and 0.08 cm, respectively; the PTV extension boundary of X, Y, and Z of group 2 was 0.12 cm, 0.2 cm, and 0.57 cm, respectively. The results showed that the thermoplastic film mesh group had better fixation efficiency.

In this study, we recommend using heat shrinkable mesh for the fixation of rectal cancer patients receiving pelvic radiotherapy, when the 6-DOF bed is used.