Fukata Kyohei, Sugimoto Satoru, Kurokawa Chie, Saito Akito, Inoue Tatsuya, Sasai Keisuke
Cancer Center, Keio University School of Medicine, 35 Shinano-machi, Shinjuku, Tokyo, Japan.
Graduate School of Medicine, Juntendo University, 2-1-1, Hongo, Bunkyo-ku, Tokyo, Japan.
Radiol Phys Technol. 2018 Jun;11(2):192-201. doi: 10.1007/s12194-018-0455-4. Epub 2018 Apr 4.
The difficulty of measuring output factor (OPF) in a small field has been frequently discussed in recent publications. This study is aimed to determine the OPF in a small field using 10-MV photon beam and stereotactic conical collimator (cone). The OPF was measured by two diode detectors (SFD, EDGE detector) and one micro-ion chamber (PinPoint 3D chamber) in a water phantom. A Monte Carlo simulation using simplified detector model was performed to obtain the correction factor for the detector measurements. About 12% OPF difference was observed in the measurement at the smallest field (7.5 mm diameter) for EDGE detector and PinPoint 3D chamber. By applying the Monte Carlo-based correction factor to the measurement, the maximum discrepancy among the three detectors was reduced to within 3%. The results indicate that determination of OPF in a small field should be carefully performed. Especially, detector choice and appropriate correction factor application are very important in this regard.
近年来的出版物中经常讨论在小射野中测量输出因子（OPF）的困难。本研究旨在使用10兆伏光子束和立体定向锥形准直器（准直器）测定小射野中的OPF。通过两个二极管探测器（SFD、EDGE探测器）和一个微型电离室（PinPoint 3D室）在水模体中测量OPF。使用简化探测器模型进行蒙特卡罗模拟，以获得探测器测量的校正因子。对于EDGE探测器和PinPoint 3D室，在最小射野（直径7.5毫米）的测量中观察到约12%的OPF差异。通过将基于蒙特卡罗的校正因子应用于测量，三个探测器之间的最大差异减小到3%以内。结果表明，小射野中OPF的测定应谨慎进行。特别是，在这方面探测器的选择和适当校正因子的应用非常重要。
