Gersh Jacob A, Willett Benjamin
Gibbs Cancer Center and Research Institute and Spectrum Medical Physics, LLC.
J Appl Clin Med Phys. 2015 Nov 8;16(6):273–280. doi: 10.1120/jacmp.v16i6.5720.
Traditional CyberKnife (CK) calibration uses TG-51, which requires kQ to be defined using the standard reference condition of 100 cm SSD in a 10 cm × 10 cm field. Since the CK is calibrated using a 6 cm fixed-aperture collimating cone at 80 cm SAD, the BJR-25 method is commonly used to relate circular-field PDDs to square-field PDDs for kQ determination. Using the InCise MLC system, the CK is able to deliver rectangular fields, allowing a more direct measurement of %dd(10 cm) using conventional reference conditions. We define the PDD correction factor (CPDD) as the ratio of %dd(10 cm) measured using CK reference conditions to that measured using standard TG-51 reference conditions. Using four ionization chambers (A1SL, CC08, CC13, and A19), %dd(10 cm) is measured using a 6 cm fixed cone at 80 cm SSD and at 100 cm SSD using an effective 10 cm × 10 cm MLC-collimated field. These values are used to calculate CPDD, while the latter is used to directly calculate a kQ value. This direct kQ value is then compared to values determined using the BJR-25 method. Using the MLC system, this study demonstrates conversion between the %dd(10 cm) measured using CyberKnife reference conditions and TG-51 reference conditions. These values provide the means for derivation of a kQ curve as a function of direct measurements of %dd(10 cm) using a 6 cm fixed-aperture collimating cone at 80 cm SSD.
传统的射波刀（CK）校准使用TG-51，这需要在10cm×10cm射野中在100cm源皮距（SSD）的标准参考条件下定义kQ。由于CK是在80cm源轴距（SAD）下使用6cm固定孔径准直器进行校准的，因此通常使用BJR-25方法将圆形射野的百分深度剂量（PDD）与方形射野的PDD相关联以确定kQ。使用InCise多叶准直器（MLC）系统，CK能够输出矩形射野，从而可以使用传统参考条件更直接地测量百分深度剂量（10cm）。我们将PDD校正因子（CPDD）定义为使用CK参考条件测量的百分深度剂量（10cm）与使用标准TG-51参考条件测量的百分深度剂量（10cm）的比值。使用四个电离室（A1SL、CC08、CC13和A19），在80cm SSD下使用6cm固定准直器以及在100cm SSD下使用有效10cm×10cm MLC准直射野测量百分深度剂量（10cm）。这些值用于计算CPDD，而CPDD则用于直接计算kQ值。然后将这个直接得到的kQ值与使用BJR-25方法确定的值进行比较。使用MLC系统，本研究展示了在射波刀参考条件和TG-51参考条件下测量的百分深度剂量（10cm）之间的转换。这些值提供了一种方法，可根据在80cm SSD下使用6cm固定孔径准直器直接测量的百分深度剂量（10cm）得出kQ曲线。
