二维电离室矩阵不同采样深度对调强验证γ通过率的影响

Influence of different sampling depths in a two-dimensional ionization chamber matrix on theγpass rate of intensity-modulated radiation therapy

选取质量保证(QA)计划中MatriXX电离室矩阵不同层面深度剂量与测量层面的剂量对比分析,探讨不同层面深度剂量对γ通过率的影响。选取21例鼻咽癌调强计划,将MatriXX和Miniphantom模体的CT影像导入计划系统作为QA模体。把调强放射治疗计划移植到QA模体重新进行剂量计算,选取从电离室腔顶部到底部5 mm高度内以1 mm等间距6个剂量层面的平面剂量,导出相应平面的剂量分布文件到MatriXX系统中和测量剂量结果进行分析,得到6组结果,记录3 mm/3%、2 mm/2%和2 mm/2%评估标准下的γ通过率。结果表明:3 mm/3%标准在Compare4、Compare5和Compare6剂量层面的γ通过率大于95.00%,均达到临床要求;3 mm/2%在Compare6剂量层面的通过率均大于95.00%,达到临床要求;3 mm/3%从Compare1的81.45%到Compare6的98.08%,提高了16.63%;3 mm/2%从Compare1的74.27%到Compare6的95.40%,提高了21.13%;2 mm/2%从Compare1的55.15%到Compare6的84.71%,提高了29.56%;Compare3层面为MatriXX侧面十字标记线高度对应的层面,将该层面剂量作为参照组,其余各组结果与该层面剂量比较均具有统计学意义(p<0.05)。在进行调强计划二维剂量分布验证,二维矩阵平行板电离室腔最底部层面深度的剂量平面作为调强放射治疗计划γ通过率验证的参考剂量平面与实际测量值对比的通过率最高。

In order to study the influence of different sampling depths in a two-dimensional ionization chamber matrix on theγpass rate,we compared and analyzed the different depth dose in the quality assurance(QA)plan and the measurement levels of the two-dimensional ionization chamber matrix(MatriXX).A total of 21 cases of nasopharyngeal carcinoma IMRT plan were selected,and the CT images of MatriXX and Miniphantom phantoms were imported into the planning system as the QA phantom.We transplanted the intensity-modulated radiation therapy plan to the QA phantom to recalculate the dose and selected the plane dose with 6 dose levels at a height of 5 mm from the top to the bottom of the ionization chamber cavity at an equal interval of 1 mm.Then,we exported the dose distribution file of the corresponding plane to the MatriXX system and analyzed the measured dose results to obtain 6 sets of results,and recorded theγpass rate under the 3 mm/3%,2 mm/2%,and 2 mm/2%evaluation standards.The results show that the pass rate of 3 mm/3%at the dose level of Compare4,Compare5,and Compare6 was greater than 95.00%,which met the clinical requirements;the pass rate of 3 mm/2%at the dose level of Compare6 was greater than 95.00%,meeting the clinical requirements.The pass rate was increased from 81.45%of Compare1 to 98.08%of Compare6 by 3 mm/3%,which was an increase of 16.63%;as well as an increase of 21.13%by 3 mm/2%from 74.27%of Compare1 to 95.40%of Compare6;and also an increase of 29.56%by 2 mm/2%from 55.15%of Compare1 to 84.71%of Compare6.The level of Compare3 was the level corresponding to the height of the cross-marker line on the side of MatriXX.The dose at this level was taken as the reference group,and the results of the other groups were statistically significant when compared with the dose at this level(p<0.05).When doing QA of an IMRT plan,the dose plane at a depth of the bottom layer of the two-dimensional ionization chamber matrix was used as the reference dose plane for the verification of the IMRT planγpass rate,which has the highest pass rate compared with the actual measured value.