Department of Radiation Oncology, Henry Ford Health System, Detroit, Michigan 48202, USA.
Med Phys. 2012 Jan;39(1):320-9. doi: 10.1118/1.3670377.
As multidetector computed tomography (MDCT) scanning is routinely performed for treatment planning in radiation oncology, understanding the characteristics of the MDCT x-ray beam is essential to accurately estimate patient dose. The purpose of this study is to characterize the x-ray beams of two commercial MDCT simulators widely used in radiation oncology by Monte Carlo (MC) simulations.
X-ray tube systems of two wide bore MDCT scanners (GE LightSpeed RT 4 and Philips Brilliance Big Bore) were modeled in the BEAMNRC/EGSNRC MC system. All the tube components were modeled from targets to bowtie filters. To validate our MC models, the authors measured half-value layers (HVL) using aluminum sheets and multifunctional radiation detectors and compared them to those obtained from MC simulations for 120 kVp beams. The authors also compared x-ray spectra obtained from MC simulation to the data provided by manufacturers. Additionally, lateral/axial beam profiles were measured in-air using radiochromic films and compared to the MC results. To understand the scatter effect, the authors also derived the scatter-to-primary energy fluence ratio (SPR) profiles and calculated the total SPR for each CT system with the CT dose index (CTDI) head and body phantoms using the BEAMNRC system.
The authors found that the HVL, x-ray spectrum and beam profiles of the MC simulations agreed well with the manufacturer-specified data within 1%-10% on average for both scanners. The total SPR were ranged from 7.8 to 13.7% for the head phantom and from 10.7 to 18.9% for the body phantom.
The authors demonstrate the full MC simulations of two commercial MDCT simulators to characterize their x-ray beams. This study may be useful to establish a patient-specific dosimetry for the MDCT systems.
由于多排螺旋 CT（MDCT）扫描常用于放射肿瘤学中的治疗计划，因此了解 MDCT X 射线束的特性对于准确估算患者剂量至关重要。本研究旨在通过蒙特卡罗（MC）模拟来描述两种广泛用于放射肿瘤学的商业 MDCT 模拟器的 X 射线束。
使用 BEAMNRC/EGSNRC MC 系统对两种宽孔径 MDCT 扫描仪（GE LightSpeed RT 4 和 Philips Brilliance Big Bore）的 X 射线管系统进行建模。从靶材到蝶形过滤器，对所有管组件进行建模。为了验证我们的 MC 模型，作者使用铝板和多功能辐射探测器测量了半价层（HVL），并将其与 MC 模拟获得的 120 kVp 光束的 HVL 进行了比较。作者还比较了 MC 模拟获得的 X 射线光谱与制造商提供的数据。此外，使用放射性胶片在空气中测量了横向/轴向束轮廓，并将其与 MC 结果进行了比较。为了了解散射效应，作者还推导了散射与初级能量注量比（SPR）的轮廓，并使用 BEAMNRC 系统计算了每个 CT 系统的总 SPR，分别使用 CT 剂量指数（CTDI）头部和身体体模。
作者发现，对于这两种扫描仪，MC 模拟的 HVL、X 射线光谱和束轮廓与制造商指定的数据在平均 1%-10%范围内吻合良好。头部体模的总 SPR 范围为 7.8%至 13.7%，身体体模的总 SPR 范围为 10.7%至 18.9%。
作者展示了两种商业 MDCT 模拟器的全 MC 模拟，以描述它们的 X 射线束。本研究可能有助于为 MDCT 系统建立患者特定的剂量学。
