Medical Physics Division, Istanbul University, Oncology Institute, Istanbul, Turkey.
Jpn J Radiol. 2010 Feb;28(2):110-6. doi: 10.1007/s11604-009-0393-5. Epub 2010 Feb 26.
High-energy photons are most commonly used in radiotherapy to treat cancer. Wedge filters are required to obtain homogeneous dose distribution in the patient. Different wedge filter types create different surface doses. In this study, the effect of the virtual and physical wedge filters on the surface and build-up region doses was examined for 6- and 18-MV high-energy photon beams.
The measurements were made in a water equivalent phantom in the build-up region at a 100-cm source-to-surface distance for various field sizes using virtual and physical wedge filters having different angles. A parallel-plate ion chamber was used to measure the percent depth doses.
The percentage dose at the surface increased as the field size increased for open, virtual, and physical wedged beams. For open, physical, and virtual wedged beams, the surface doses were found to be 15.4%, 9.9%, and 15.9% with 6-MV photons and 10.6%, 8.8%, 11.9% with 18-MV photons, respectively, at 10 x 10 cm(2) field size.
Build-up doses of virtual wedged beams were similar to those of open beams. Surface and buildup doses of physical wedged beams were lower than those of open and virtual wedged beams.
高能光子最常用于治疗癌症的放射治疗。楔形滤波器是获得患者体内均匀剂量分布所必需的。不同类型的楔形滤波器会产生不同的表面剂量。在这项研究中，检查了 6 和 18 兆伏高能光子束的虚拟和物理楔形滤波器对表面和建区剂量的影响。
在源皮距为 100cm 的水等效体模中，在不同射野大小下，使用具有不同角度的虚拟和物理楔形滤波器，在建区进行了测量。使用平行板电离室测量百分深度剂量。
对于开野、虚拟和物理楔形射束，随着射野的增大，表面剂量增加。对于 6-MV 光子，在 10×10cm(2)射野大小下，开野、物理和虚拟楔形射束的表面剂量分别为 15.4%、9.9%和 15.9%；对于 18-MV 光子，开野、物理和虚拟楔形射束的表面剂量分别为 10.6%、8.8%和 11.9%。
虚拟楔形射束的建区剂量与开野相似。物理楔形射束的表面和建区剂量低于开野和虚拟楔形射束。
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