Oderinde Oluwaseyi Michael, du Plessis Freek
Department of Medical Physics, University of the Free State, PO Box 339, Bloemfontein 9300, South Africa.
Rep Pract Oncol Radiother. 2019 Sep-Oct;24(5):462-471. doi: 10.1016/j.rpor.2019.07.007. Epub 2019 Aug 2.
This study focused on evaluating the sensitivity of integral quality monitoring (IQM®) system and MatriXX detectors. These two detectors are recommended for radiotherapy pre-treatment quality assurance (QA).
IQM is a large wedged-shaped ionisation chamber mounted to the linear accelerator (linac) head in practice. MatriXX consists of an array of ionisation chambers also attached to the linac head.
In this study, the dosimetric performance and sensitivity of MatriXX and IQM detectors were evaluated using the following characteristics: reproducibility, linearity, error detection capability and three-dimensional conformal radiotherapy (3D-CRT) plans of the head and neck, thorax and pelvic regions.
This study indicates that the signal responses of the large ionisation chamber device (IQM) and the small pixel array of ionisation chambers device (MatriXX) are reproducible, linear and sensitive to MLC positional errors, backup jaw positional errors and dose errors. The local percentage differences for dose errors of 1%, 2%, and 3% were, respectively, within 0.35-8.23%, 0.78-16.21%, and 1.10-24.41% for the IQM device. While for the MatriXX detector, the ranges were between 0.24-3.19, 0.57-6.43 and 0.81-12.95, respectively. Since IQM is essentially a double wedge-shaped large ionisation chamber, its reproducibility and detection capability are competitive to that of MatriXX. In addition, the sensitivity of the two QA systems increases with an increase in escalation percentage, and the signal responses are patient plan specific.
The two detectors response signals have good correlations and they are accurate for pre-treatment QA. Statistically, ( < 0.05) there is a significant difference between the IQM and MatriXX response to dose errors.
本研究着重评估积分质量监测（IQM®）系统和MatriXX探测器的灵敏度。这两种探测器被推荐用于放射治疗预处理质量保证（QA）。
实际上，IQM是安装在线性加速器（直线加速器）机头的大型楔形电离室。MatriXX由同样连接在直线加速器机头上的一系列电离室组成。
在本研究中，使用以下特性评估MatriXX和IQM探测器的剂量学性能和灵敏度：可重复性、线性、误差检测能力以及头颈部、胸部和盆腔区域的三维适形放射治疗（3D-CRT）计划。
本研究表明，大型电离室装置（IQM）和小型电离室像素阵列装置（MatriXX）的信号响应具有可重复性、线性，并且对多叶准直器（MLC）位置误差、备用挡块位置误差和剂量误差敏感。对于IQM装置，1%、2%和3%剂量误差的局部百分比差异分别在0.35 - 8.23%、0.78 - 16.21%和1.10 - 24.41%范围内。而对于MatriXX探测器，范围分别在0.24 - 3.19、0.57 - 6.43和0.81 - 12.95之间。由于IQM本质上是一个双楔形大型电离室，其可重复性和检测能力与MatriXX相当。此外，两种QA系统的灵敏度随着剂量递增百分比的增加而增加，并且信号响应是患者计划特异性的。
两种探测器的响应信号具有良好的相关性，并且对于预处理QA是准确的。从统计学角度（P < 0.05），IQM和MatriXX对剂量误差的响应存在显著差异。
