Araki F, Kubo H D, Yang C, Ikegami T, Ishidoya T
Department of Radiological Technology, Kumamoto University College of Medical Science.
Nihon Hoshasen Gijutsu Gakkai Zasshi. 2004 Jan;60(1):67-8. doi: 10.6009/jjrt.kj00000922258.
A radiophotoluminescent (RPL) glass rod dosimeter (GRD) and a small active volume p-type silicon diode detector (stereotactic field detector, SFD) were used for the measurement of Gamma-Knife output factors. All measurements were done using a 16 cm diameter spherical polystyrene phantom with the detector at the focal spot of Gamma-Knife. The GRD system consists of small rod-shaped glass chip detectors and an automatic readout device. The output factors measured with GRD of the 14, 8 and 4 mm helmets relative to the 18 mm helmet are 0.981, 0.942 and 0.877, respectively. Similarly, the corresponding output factors measured with SFD are 0.980, 0.949 and 0.867, respectively. These output factors are comparable with the values given in a recent publication and the values recommended by Elekta, the manufacture. The angular dependence of these detectors is also measured using a linear accelerator-based stereotactic radiosurgery system. For the Gamma-Knife angle ranging from 6 to 36 degrees from the vertical axis, the measured angular dependence of the GRD is approximately 1.0% at a 4 MV x-ray beam. The response of SFD indicates approximately 3-4% directional dependence for the same angle range for a 6 MV x-ray beam. The Gamma-Knife helmet output factors measured with SFD are corrected for angular dependence. In summary, GRD can be a good candidate in measuring small field output factor. Due to an angular dependence the small p-type diode detector needs care when calculating the Gamma-Knife dose.
使用放射性光致发光（RPL）玻璃棒剂量计（GRD）和小灵敏体积的p型硅二极管探测器（立体定向野探测器，SFD）来测量伽马刀输出因子。所有测量均使用直径16 cm的球形聚苯乙烯模体，探测器置于伽马刀的焦点处。GRD系统由小棒状玻璃芯片探测器和自动读出装置组成。用GRD测量的14、8和4 mm准直器相对于18 mm准直器的输出因子分别为0.981、0.942和0.877。同样，用SFD测量的相应输出因子分别为0.980、0.949和0.867。这些输出因子与最近一篇出版物中给出的值以及制造商Elekta推荐的值相当。还使用基于直线加速器的立体定向放射外科系统测量了这些探测器的角度依赖性。对于伽马刀与垂直轴成6至36度的角度范围，在4 MV X射线束下测量的GRD角度依赖性约为1.0%。对于6 MV X射线束，在相同角度范围内，SFD的响应表明方向依赖性约为3 - 4%。用SFD测量的伽马刀准直器输出因子针对角度依赖性进行了校正。总之，GRD可以是测量小射野输出因子的良好候选者。由于存在角度依赖性，在计算伽马刀剂量时，小p型二极管探测器需要谨慎使用。
