Department for Physics and Biophysics, School of Medicine, University of Zagreb, Zagreb, Croatia.
Department for Medical Physics, University Hospital Centre Zagreb, Zagreb, Croatia.
J Appl Clin Med Phys. 2023 Oct;24(10):e14109. doi: 10.1002/acm2.14109. Epub 2023 Aug 25.
The purpose of this study is to calculate volume averaging correction factors for detectors used in the dosimetry of Gamma Knife's narrow photon beams, and to determine the impact of volume averaging on the field output correction factor.
Simulations of different Gamma Knife fields were done using elliptical dose model formalism with newly introduced fit functions. To determine volume averaging correction factors a calculation of the absorbed dose over the volume of the detector was performed. The elliptical dose model was tested with respect to absorbed dose distribution for different volumes and compared with the calculations of Leksell GammaPlan v.11.3.1.
The largest differences in absorbed dose calculated by the elliptical model and Leksell GammaPlan are 2.25%, 1.5%, and 0.6% for 16, 8, and 4 mm field sizes, respectively. Volume averaging correction factors were determined for six ionization chambers, five semiconductor detectors, a diamond, and two plastic scintillator detectors. In general, for all examined detectors the impact of volume averaging is more pronounced for smaller field sizes. All studied ionization chambers had a larger volume than other detectors, therefore the volume averaging correction factors for ionization chambers are larger for all investigated field sizes. Besides the fact that plastic scintillator detectors can be considered tissue-equivalent, volume averaging correction factor should be applied.
Volume averaging correction factors for different detectors are determined and suitable detectors for dosimetry of Gamma Knife's narrow photon beams are recommended. It is shown that volume averaging has a dominant contribution to a field output correction factor.
本研究旨在计算伽玛刀窄光子束剂量学中使用的探测器的体素平均校正因子，并确定体素平均对射野输出校正因子的影响。
使用新引入的拟合函数，通过椭圆剂量模型公式对不同的伽玛刀射野进行模拟。为了确定体素平均校正因子，对探测器体积内的吸收剂量进行了计算。对椭圆剂量模型进行了测试，以评估不同体积的吸收剂量分布，并与 Leksell GammaPlan v.11.3.1 的计算结果进行了比较。
椭圆模型与 Leksell GammaPlan 计算的吸收剂量最大差异分别为 16、8 和 4mm 射野大小时为 2.25%、1.5%和 0.6%。为六个电离室、五个半导体探测器、一个金刚石和两个塑料闪烁体探测器确定了体素平均校正因子。一般来说，对于所有检查的探测器，体素平均对较小射野的影响更为明显。所有研究的电离室的体积都大于其他探测器，因此，所有研究的射野大小的电离室的体素平均校正因子都较大。除了塑料闪烁体探测器可以被认为是组织等效的事实外，还应应用体素平均校正因子。
确定了不同探测器的体素平均校正因子，并推荐了适合伽玛刀窄光子束剂量学的探测器。结果表明，体素平均对射野输出校正因子有主要贡献。
