腘窝固定法减少宫颈癌外照射放疗摆位误差的价值

Value of Popliteal Fossa Fixation Method in Reducing Setup Errors for External Irradiation Therapy in Cervical Cancer Patients

[目的]通过对比传统真空垫固定法与腘窝固定法在宫颈癌外照射放疗中摆位误差的优劣,探索一种简单有效的体位固定方法。[方法]两组宫颈癌患者分别采用传统真空垫固定法(传统组)和腘窝固定法(改进组),通过Varian TrueBeam治疗系统的锥形束CT(CBCT)在治疗过程中定期采集摆位误差数据用于比较分析,并依据Van Herk外扩边界计算公式计算两种固定法的计划靶体积(PTV)外扩值。分别以两种外扩值建立新的PTV并计算危及器官照射体积。[结果]传统组与改进组X/Y/Z轴向上PTV外扩值分别为0.63cm、0.65cm、0.76cm和0.61cm、061cm、0.58cm。依据改进组外扩值建立靶区可以显著减少PTV及膀胱、直肠、小肠、骨盆的照射体积(P值均为0.000)。改进组降低了Y轴上误差的倾向性(P值为0.029),缩小了向左,向头、向腹部及向背部的误差大小,传统组及改进组在上述4个方向上的误差分别为:(0.29±0.20)cm、(0.25±0.23)cm、(0.27±0.18)cm、(0.30±0.26)cm和(0.22±0.16)cm、(0.17±0.13)cm、(0.18±0.17)cm、(0.23±0.17)cm,P值分别为0.001、0.000、0.001和0.001。[结论 ]腘窝固定法缩小了宫颈癌外照射放疗所需PTV外扩值,减少了PTV及正常器官照射体积,是一种有效的体位固定方法。

[Objective] To compare the traditional vacuum pad fixation method and popliteal fossa fixation method for external irradiation therapy in cervical cancer patients. [Methods] One hundred and ten patients with cervical cancer receiving external irradiation therapy were divided into two groups ：traditional vacuum pad fixation method was employed in 58 patients（routine group）and popliteal fossa fixation method was employed in 52 patients（improved group）. The data of body position setup errors were obtained via cone beam CT（CBCT） of Varian True Beam treatment system. Van Herk expanding margin formula was applied to calculate the value of PTV expansion for two groups. Two new PTVs were established with two groups of PTV expansion value and then the organ at risk（OAR） irradiated volumes were calculated by means of MIM software. [Results]The PTV expansion value in X/Y/Z axis was 0.63 cm,0.65 cm,0.76 cm in routine group and0.61 cm,0.61 cm,0.58 cm in improved group respectively. The PTV established on the expansion value obtained from improved group was significantly reduced as well as the irradiated volume of bladder,rectum,small intestine and pelvis（P=0.000）. The popliteal fossa fixation method reduced the directional tendency of setup errors in Y axis（P=0.029） as well as the magnitude of setup errors of the leftward,headward,ventrad and dorsad,and the setup errors value of these four orientation in the routine group and improved group were（0.29±0.20）cm,（0.25 ±0.23）cm,（0.27±0.18）cm,（0.30±0.26）cm and（0.22±0.16）cm,（0.17±0.13）cm,（0.18±0.17）cm,（0.23±0.17）cm,with a P value of above four orientation were 0.001,0.000,0.001 and 0.001 respectively. [Conclusion] Popliteal fossa fixation method can effectively reduce the value of PTV expansion together with the PTV and OAR irradiated volume in cervical cancer radiotherapy.