Weber Carolin, Kranzer Rafael, Weidner Jan, Kröninger Kevin, Poppe Björn, Looe Hui Khee, Poppinga Daniela
PTW Freiburg, Freiburg, 79115, Germany.
TU Dortmund University, Dortmund, 44227, Germany.
Med Phys. 2020 Jul;47(7):3165-3173. doi: 10.1002/mp.14149. Epub 2020 Apr 13.
The aim of this study is the experimental and Monte Carlo-based determination of small field correction factors for the unshielded silicon detector microSilicon for a standard linear accelerator as well as the Cyberknife System. In addition, a detailed Monte Carlo analysis has been performed by modifying the detector models stepwise to study the influences of the detector's components.
Small field output correction factors have been determined for the new unshielded silicon diode detector, microSilicon (type 60023, PTW Freiburg, Germany) as well as for the predecessors Diode E (type 60017, PTW Freiburg, Germany) and Diode SRS (type 60018, PTW Freiburg, Germany) for a Varian TrueBeam linear accelerator at 6 MV and a Cyberknife system. For the experimental determination, an Exradin W1 scintillation detector (Standard Imaging, Middleton, USA) has been used as reference. The Monte Carlo simulations have been performed with EGSnrc and phase space files from IAEA as well as detector models according to manufacturer blueprints. To investigate the influence of the detector's components, the detector models have been modified stepwise.
The correction factors for the smallest field size investigated at the TrueBeam linear accelerator (equivalent dosimetric square field side length S = 6.3 mm) are 0.983 and 0.939 for the microSilicon and Diode E, respectively. At the Cyberknife system, the correction factors of the microSilicon are 0.967 at the smallest 5-mm collimator compared to 0.928 for the Diode SRS. Monte Carlo simulations show comparable results from the measurements and literature.
The microSilicon (type 60023) detector requires less correction than its predecessors, Diode E (type 60017) and Diode SRS (type 60018). The detector housing has been demonstrated to cause the largest perturbation, mainly due to the enhanced density of the epoxy encapsulation surrounding the silicon chip. This density has been rendered more water equivalent in case of the microSilicon detector to minimize the associated perturbation. The sensitive volume itself has been shown not to cause observable field size-dependent perturbation except for the volume-averaging effect, where the slightly larger diameter of the sensitive volume of the microSilicon (1.5 mm) is still small at the smallest field size investigated with corrections <2%. The new microSilicon fulfils the 5% correction limit recommended by the TRS 483 for output factor measurements at all conditions investigated in this work.
本研究旨在通过实验和基于蒙特卡洛方法，确定用于标准直线加速器以及射波刀系统的非屏蔽硅探测器microSilicon的小射野校正因子。此外，通过逐步修改探测器模型进行了详细的蒙特卡洛分析，以研究探测器各组件的影响。
已针对新型非屏蔽硅二极管探测器microSilicon（型号60023，德国PTW弗莱堡）以及其前身二极管E（型号60017，德国PTW弗莱堡）和二极管SRS（型号60018，德国PTW弗莱堡），在瓦里安TrueBeam直线加速器6 MV能量下以及射波刀系统中确定了小射野输出校正因子。在实验测定中，使用了Exradin W1闪烁探测器（美国标准成像公司，米德尔顿）作为参考。利用EGSnrc以及来自国际原子能机构的相空间文件和根据制造商蓝图建立的探测器模型进行了蒙特卡洛模拟。为了研究探测器各组件的影响，逐步修改了探测器模型。
在TrueBeam直线加速器上研究的最小射野尺寸（等效剂量学方形射野边长S = 6.3 mm）下，microSilicon和二极管E的校正因子分别为0.983和0.939。在射波刀系统中，与二极管SRS的0.928相比，microSilicon在最小5 mm准直器下的校正因子为0.967。蒙特卡洛模拟结果与测量值及文献结果相当。
microSilicon（型号60023）探测器相比其前身二极管E（型号60017）和二极管SRS（型号60018）需要更少的校正。已证明探测器外壳引起的扰动最大，主要是由于硅芯片周围环氧封装的密度增加。在microSilicon探测器中，已使这种密度更接近水等效，以尽量减少相关扰动。除了体积平均效应外，敏感体积本身并未显示出会引起可观察到的与射野尺寸相关的扰动，在本研究中所研究的最小射野尺寸下，microSilicon敏感体积稍大的直径（1.5 mm）校正后仍较小，小于2%。在本工作所研究的所有条件下，新型microSilicon满足TRS 483推荐的输出因子测量5%的校正限值。
