调强验证中MapCheck对加速器机架与准直器角度敏感性研究

目的研究MapCheck静态调强放射治疗中加速器机架与准直器角度的改变对不同阈值下验证通过率的影响,并分析其对角度变化的敏感性。方法选择2018年12月于福建省肿瘤医院行静态调强放射治疗的10例恶性肿瘤患者,其中男性7例,女性3例;年龄30~74岁,中位年龄52岁。使用MapCheck2作为验证工具。设定机架角度为0°、5°、10°、15°、20°、25°、30°和准直器角度为0°、2°、3°、4°、5°、10°时,进行调强计划验证,分别记录在1%/1 mm和10%、2%/2 mm和10%、3%/3 mm和10%阈值下等剂量距离偏差(DTA)和γ通过率,并使用配对t检验分析数据。结果机架角度组:在1%/1 mm标准下,角度变化为0°~10°,验证通过率出现上下波动,波动范围为80.68%±4.42%;角度变化为10°~30°,角度平均每增加5°,平均验证通过率降幅为11.24%±1.30%。在2%/2 mm、3%/3 mm标准下,当角度变化为0°~15°,验证通过率降幅分别为1.98%±0.31%、1.23%±0.39%;当角度变化为15°~30°,角度平均每增加5°,验证通过率降幅分别为12.66%±0.27%、9.25%±0.33%。准直器角度组:在1%/1 mm标准下,准直器角度变化为0°~10°,角度平均每增加1°,验证通过率降幅为4.83%±0.47%。在2%/2 mm、3%/3 mm标准下,角度变化为0°~2°,验证通过率降幅分别为2.85%±0.29%、0.60%±0.19%;当角度变化为2°~10°,角度平均每增加1°,验证通过率降幅分别为4.21%±0.17%、2.86%±0.13%。结论当阈值设置为2%/2 mm和10%、3%/3 mm和10%时,MapCheck弱化了可能存在的机架与准直器角度误差和计划自身的缺陷对通过率所造成的影响,因此建议在调强验证中将阈值设置为1%/1 mm和10%并确保机架尤其是准直器到位精度,以保证调强验证的精确性。

Sensitivity of MapCheck for intensity-modulated verification on gantry and collimator angle

Objective To investigate the influence of changes in gantry and collimator angle on passing rate of MapCheck for intensity modulated radiation therapy(IMRT)verification,and analysis sensitivity of MapCheck on angle change.Methods A total of 10 patients treated with IMRT at Fujian Cancer Hospital in December 2018 were enrolled,which included 7 males and3 females,aged 30-74 years old with median age of 52 years old.The MapCheck2 was used to verify passing rate.The IMRT modulation verification performed to fix gantry angle at 0°,5°,10°,15°,20°,25°,30°and collimator angle at 0°,2°,3°,4°,5°,10°,respectively.The equivalent dose distance to agreement(DTA)andγpass rate were recorded at threshold 1%/1 mm and10%,2%/2 mm and 10%,3%/3 mm and 10%,respectively;Paired t-test was used to analyze pass rates.Results Gantry group:at 1%/1 mm,gantry angle changed from 0°to 10°,the verification pass rate fluctuated up and down with fluctuation range of 80.68%±4.42%;in the angle changed of 10°-30°,when mean angle increased 5°,the mean verification pass rate decreased 11.24%±1.30%.At 2%/2 mm and 3%/3 mm,gantry angle changed 0°-15°,verification pass rate decreased1.98%±0.31%and 1.23%±0.39%.The angle changed 15°-30°,when mean angle increased 5°,the mean verification pass rate decreased 12.66%±0.27%and 9.25%±0.33%.Collimator group:at 1%/1 mm,collimator angle changed 0°-10°,when mean angle increased 1°,the mean verification pass rate decreased 4.83%±0.47%.At 2%/2 mm and 3%/3 mm,collimator angle changed 0°-2°,verification pass rate decreased 2.85%±0.29%,0.60%±0.19%;collimation angle changed 2°-10°,mean angle increased 1°,the mean verification pass rate decreased 4.21%±0.17%and 2.86%±0.13%.Conclusion It is demonstrated that MapCheck attenuates the influence of pass rate caused by gantry and collimator angle errors or plan defects,when threshold is set at 2%/2 mm and 10%or 3%/3 mm and 10%.Therefore,it is recommended to set threshold at 1%/1 mm and 10%and gantry,especially accuracy of collimator to ensure the accuracy of intensity modulation verification.