肿瘤运动对磁共振引导放射治疗剂量分布影响的研究

Effect of tumor movement on dose distribution of magnetic resonance guided radiotherapy

目的旨在通过端到端测试验证磁共振直线加速器(MRI-Linac)剂量照射的准确性,评估自适应计划对不同运动模式剂量保证的可靠性。方法使用磁共振兼容的运动模体(CIRS 008Z),设定6种运动模式进行端到端测试,在MR-linac(医科达Unity,1.5T)进行剂量照射,对比5种运动模式剂量与标准运动模式剂量的差异。使用Arc Check评估针对不同运动模式制定的放疗计划,当计划符合临床标准后,将剂量照射实验重复3次,记录每次自适应放疗靶区和危及器官相应的DVH参数。采用SPSS 22.0对结果进行统计分析。结果6种呼吸模式对应的计划在3%/3 mm、3%/2 mm和2%/2 mm条件下的伽马通过率均>95%。另外,生成的所有在线自适应计划也符合本研究设定的临床标准。在靶区内,5种运动模式的GTV D98(t=5977.20,P<0.001)、D95(t=6028.67,P=0.001)、D50(t=6222.83,P=0.011)、D2(t=6457.90,P=0.001)和Dmax(t=6814.47,P<0.001),与COS4-AP比较差异有统计学意义。GTV D98、D95、D50、D2参数的平均剂量与标准运动模式的差异较小(<1%)。危及器官5种运动模式的双侧肺组织D20(t=552.83,P=0.001)和D30(t=329.13,P=0.001)、左肺D20(t=1292.40,P<0.001)和肾Dmean(t=373.37,P=0.020)、脊髓Dmax(t=2729.27,P=0.011)和D2(t=2266.77,P<0.001),与COS4-AP比较差异有统计学意义。肺组织D20和D30、左肺D20、肾Dmean、脊髓Dmax和D2参数的平均剂量与标准运动模式相比,变化率较大,最大为21.69%。结论MR-Linac的剂量具有准确性。不同运动模式的自适应计划的靶区剂量体积直方图(DVH)剂量参数差异较小,自适应计划对不同运动模式剂量保证具有可靠性。

Objective To verify the accuracy of MR-Linac dose delivery through the end-to-end test and to evaluate the reliability of the adaptive plan for dose assurance.Methods A magnetic resonance compatible motion phantom(CIRS 008 Z)was employed and six motion patterns were set for the end-to-end test.The dose of MR-linac(Elekta Unity,1.5 T)was used to compare the difference between five motion patterns dose and the standard motion pattern dose.Arc Check was used to evaluate the radiotherapy plan for different motion patterns.When the plan met the clinical criteria,the dose projection experiment was repeated three times,and the corresponding DVH parameters of each adaptive radiotherapy target and organs at risk were recorded.Finally,SPSS 22.0 was used to analyze the results.Results The gamma passing rate were greater than 95%under 3%/3 mm,3%/2 mm and 2%/2 mm conditions.The overall differences among five motion patterns of GTVD98(t=5977.20,P<0.001),D95(t=6028.67,P=0.001),D50(t=6222.83,P=0.011),D2(t=6457.90,P=0.001),Dmax(t=6814.47,P<0.001)and COS4-AP were statistically significant.The difference between the average dose of GTVD98,D95,D50,D2 parameters of different motion patterns and the standard motion pattern was small,and the percentage of difference was less than 1%.For the organs at risk,the overall differences among five motion patterns of D20(t=552.83,P=0.001)and D30(t=329.13,P=0.001)in bilateral lung,D20(t=1292.40,P<0.001)and Dmean(t=373.37,P=0.020)in left lung,Dmax(t=2729.27,P=0.011)and D2(t=2266.77,P<0.001)in spinal cord and COS4-AP were statistically significant.The average doses of lung tissue D20 and D30,left lung D20,kidney Dmean,spinal cord Dmax and D2 parameters changed significantly compared with the standard motion pattern,the max different rate was 21.69%.Conclusions The dose of MR-Linac was accurate.In the target,the DVH dose parameters had little difference of adaptive planning with different motion patterns,and the adaptive planning has reliable for different motion patterns.