Palta J R, Yeung D K, Frouhar V
Department of Radiation Oncology, University of Florida, College of Medicine, Gainesville 32610-0385, USA.
Med Phys. 1996 Jul;23(7):1219-24. doi: 10.1118/1.597678.
A commercial linear accelerator with a factory-fitted multileaf collimator (MLC) was commissioned for clinical use. Measurements made of dosimetric parameters included central axis depth-dose, field-size factors, wedge factors, penumbra, and leaf leakage for the 6-MV and 15-MV photon beams available on this accelerator. The depth-dose characteristics, output factors, and transmission factors were similar to those reported in the literature for a machine by the same manufacturer with a standard treatment head. Because of scalloping, the effective penumbra for the MLC was 3 to 4 mm wider than that for the conventional collimator jaws. The output for the fields shaped by the MLC was generally lower than that for similar fields shaped with Lipowitz's metal (Cerrobend). The magnitude of the difference was field-size dependent and ranged from 0.5% to 4.5% for open shaped fields, increasing to 1% to 5% in the presence of wedges. Further analysis of this observation has shown it to be primarily due to differences in the scattered radiation from the collimator head.
一台配备了工厂预装多叶准直器（MLC）的商用直线加速器被投入临床使用。对剂量学参数的测量包括该加速器上6兆伏和15兆伏光子束的中心轴深度剂量、射野大小因子、楔形因子、半值层和叶片泄漏。深度剂量特性、输出因子和透射因子与文献中报道的同一制造商生产的具有标准治疗头的机器的这些参数相似。由于扇形，MLC的有效半值层比传统准直器钳口的有效半值层宽3至4毫米。MLC形成的射野的输出通常低于用Lipowitz金属（Cerrobend）形成的类似射野的输出。差异的大小取决于射野大小，对于开放形状的射野，差异范围为0.5%至4.5%，在有楔形物的情况下增加到1%至5%。对这一观察结果的进一步分析表明，这主要是由于准直器头部散射辐射的差异。
