Li Jonathan G, Yan Guanghua, Liu Chihray
Department of Radiation Oncology, University Of Florida, Gainesville, FL, 32610-0385.
Department of Nuclear and Radiological Engineering, University of Florida, Gainesville, FL, 32611-8300, U.S.A.
J Appl Clin Med Phys. 2009 Apr 29;10(2):62-74. doi: 10.1120/jacmp.v10i2.2942.
Two commercially available detector arrays were compared for their use in the quality assurance of patient-specific IMRT treatment plans: one a diode-based array (MapCHECK) and the other an ion chamber-based array (MatriXX). The dependence of the response of detectors on the field size, dose rate, and radiation energy were measured and compared with reference measurements using a Farmer-type ionization chamber. The linearity of the detector response, short-term and long-term reproducibility, statistical uncertainty as a function of delivered dose, and the validity of the array calibration were also examined to understand the stability and uncertainty of the systems. No field size or SSD dependence were observed within the range of the field sizes and SSDs used in the study at both 6 MV and 18 MV photon energies. Both detector arrays showed negligible errors (< 1%) when measuring doses of more than ~8 cGy, but exhibited errors of ~3% when measuring doses on the order of 1 cGy. While the MapCHECK showed a stable short-term reproducibility to within the measurement errors, the MatriXX showed a slow but continuously increase in reading during the one-hour period (about 0.8%). The MapCHECK also showed a slightly better array sensitivity correction with all the detectors having less than 1% discrepancy and more than 90% of the detectors within 0.5% variation, whereas about 60% of the MatriXX detectors showed a less than 0.5% variation and approximately 8% exhibited a larger than 1% discrepancy. MatriXX detectors also displayed a volume-averaging effect consistent with its detector size of approximately 4.5 mm in diameter. Excellent passing rates were obtained for both detector arrays when compared with the planar dose distributions from the treatment planning system for three 6 MV IMRT fields and three 18 MV IMRT fields after the volume-averaging effect of the MatriXX was taken into account.
对两种商用探测器阵列在特定患者调强放射治疗（IMRT）计划质量保证中的应用进行了比较：一种是基于二极管的阵列（MapCHECK），另一种是基于电离室的阵列（MatriXX）。测量了探测器响应与射野大小、剂量率和辐射能量的相关性，并与使用 Farmer 型电离室的参考测量值进行了比较。还研究了探测器响应的线性、短期和长期重复性、作为剂量函数的统计不确定性以及阵列校准的有效性，以了解系统的稳定性和不确定性。在本研究使用的 6 MV 和 18 MV 光子能量的射野大小和源皮距（SSD）范围内，未观察到对射野大小或 SSD 的依赖性。当测量剂量超过约 8 cGy 时，两种探测器阵列的误差均可忽略不计（<1%），但在测量剂量约为 1 cGy 时，误差约为 3%。虽然 MapCHECK 在测量误差范围内显示出稳定的短期重复性，但 MatriXX 在一小时内读数缓慢但持续增加（约 0.8%）。MapCHECK 还显示出稍好的阵列灵敏度校正，所有探测器的差异小于 1%，超过 90%的探测器变化在 0.5%以内，而约 60%的 MatriXX 探测器变化小于 0.5%，约 8%的探测器差异大于 1%。MatriXX 探测器还表现出与其直径约 4.5 mm 的探测器尺寸一致的体积平均效应。在考虑 MatriXX 的体积平均效应后，将两种探测器阵列与三个 6 MV IMRT 射野和三个 18 MV IMRT 射野的治疗计划系统的平面剂量分布进行比较时，均获得了优异的通过率。
