Department of Radiation Oncology, School of Medicine, Vanderbilt-Ingram Cancer Center, Vanderbilt University, B-902, TVC, 1301 Medical Center Drive, Nashville, TN 37232-5671, USA.
Phys Med Biol. 2010 Sep 7;55(17):5231-48. doi: 10.1088/0031-9155/55/17/022. Epub 2010 Aug 16.
This study presents beam characteristics of five recently available x-ray beams produced by an on-board imager (OBI 1.4) for acquiring kilovoltage cone-beam computed tomography (kV-CBCT) and investigates suitable methods for the beam radiation output determination resulting from an image acquisition. Both are essential for commissioning an x-ray beam in a radiotherapy treatment planning system. The BEAM/DOSXYZnrc Monte Carlo codes were used in the investigation. The simulated beam data were benchmarked against measurements. Three different commercially available plastic phantom materials are investigated as liquid water substitutes in the beam radiation output determination. Ionization chambers are used for the measurements. Five kV-CBCT beam characteristics including photon fluence, average beam energy and photon spectra are generated from Monte Carlo simulations. The Monte Carlo calculated dose profiles are validated by measurements. The fluence of kV-CBCT beams is strongly dependent on the geometry of added filters as well as X and Y beam collimations. The potential errors of determining the beam output of a kV-CBCT beam in Solid Water and PMMA phantoms may approach 8% and 20%, respectively, for use in a conventional treatment planning system, whereas using the Plastic Water low-energy range (PW-LR) phantom results in errors within 2%. The Monte Carlo simulation is essential in providing the parameters of an x-ray beam which are needed for the commissioning of a kV-CBCT beam in a radiotherapy treatment planning system. The PW-LR phantom is a suitable liquid water substitute in the beam output determination resulting from a kV-CBCT acquisition.
本研究介绍了五种最近可用的 X 射线束的射线束特性，这些射线束由机载成像仪（OBI 1.4）产生，用于获取千伏锥形束计算机断层扫描（kV-CBCT），并研究了适合于由于图像采集而导致的射线辐射输出确定的方法。这两者对于在放射治疗计划系统中调试 X 射线束都是必不可少的。BEAM/DOSXYZnrc 蒙特卡罗代码用于研究。模拟的射线束数据与测量值进行了基准测试。作为射线辐射输出确定中的水替代品，研究了三种不同的市售塑料体模材料。使用电离室进行测量。从蒙特卡罗模拟生成了包括光子通量，平均束能量和光子能谱在内的五种 kV-CBCT 射线束特性。通过测量验证了蒙特卡罗计算的剂量分布。kV-CBCT 射线束的通量强烈依赖于添加滤波器以及 X 和 Y 射线准直的几何形状。在常规治疗计划系统中，在固体水和 PMMA 体模中确定 kV-CBCT 束输出时，潜在的误差可能分别接近 8％和 20％，而在使用低能范围（PW-LR）体模时，误差在 2％以内。在为放射治疗计划系统中的 kV-CBCT 束调试提供所需的 X 射线束参数方面，蒙特卡罗模拟是必不可少的。PW-LR 体模是用于 kV-CBCT 采集导致的射线辐射输出确定的合适的水替代品。
