Toshiba America Medical Systems, 2441 Michelle Drive, Tustin, California 92780, USA.
Med Phys. 2013 Sep;40(9):091901. doi: 10.1118/1.4816652.
CT neuroperfusion examinations are capable of delivering high radiation dose to the skin or lens of the eyes of a patient and can possibly cause deterministic radiation injury. The purpose of this study is to: (a) estimate peak skin dose and eye lens dose from CT neuroperfusion examinations based on several voxelized adult patient models of different head size and (b) investigate how well those doses can be approximated by some commonly used CT dose metrics or tools, such as CTDIvol, American Association of Physicists in Medicine (AAPM) Report No. 111 style peak dose measurements, and the ImPACT organ dose calculator spreadsheet.
Monte Carlo simulation methods were used to estimate peak skin and eye lens dose on voxelized patient models, including GSF's Irene, Frank, Donna, and Golem, on four scanners from the major manufacturers at the widest collimation under all available tube potentials. Doses were reported on a per 100 mAs basis. CTDIvol measurements for a 16 cm CTDI phantom, AAPM Report No. 111 style peak dose measurements, and ImPACT calculations were performed for available scanners at all tube potentials. These were then compared with results from Monte Carlo simulations.
The dose variations across the different voxelized patient models were small. Dependent on the tube potential and scanner and patient model, CTDIvol values overestimated peak skin dose by 26%-65%, and overestimated eye lens dose by 33%-106%, when compared to Monte Carlo simulations. AAPM Report No. 111 style measurements were much closer to peak skin estimates ranging from a 14% underestimate to a 33% overestimate, and with eye lens dose estimates ranging from a 9% underestimate to a 66% overestimate. The ImPACT spreadsheet overestimated eye lens dose by 2%-82% relative to voxelized model simulations.
CTDIvol consistently overestimates dose to eye lens and skin. The ImPACT tool also overestimated dose to eye lenses. As such they are still useful as a conservative predictor of dose for CT neuroperfusion studies. AAPM Report No. 111 style measurements are a better predictor of both peak skin and eye lens dose than CTDIvol and ImPACT for the patient models used in this study. It should be remembered that both the AAPM Report No. 111 peak dose metric and CTDIvol dose metric are dose indices and were not intended to represent actual organ doses.
CT 神经灌注检查会对患者的皮肤或眼睛晶状体造成高剂量辐射，并可能导致确定性辐射损伤。本研究的目的是：（a）根据几种不同头部大小的体素化成人患者模型，估算 CT 神经灌注检查的峰值皮肤剂量和晶状体剂量；（b）研究这些剂量如何通过一些常用的 CT 剂量指标或工具（如 CTDIvol、美国医学物理学家协会（AAPM）第 111 号报告中的峰值剂量测量值以及 ImPACT 器官剂量计算器电子表格）进行近似估算。
使用蒙特卡罗模拟方法估算体素化患者模型（包括 GSF 的 Irene、Frank、Donna 和 Golem）的峰值皮肤和晶状体剂量，这些模型基于四个主要制造商的四个扫描仪，在所有可用管电压下采用最宽的准直器。剂量以每 100mAs 为单位报告。对 16cm CTDI 体模进行 CTDIvol 测量，对可用的所有管电压进行 AAPM 第 111 号报告中的峰值剂量测量值和 ImPACT 计算。然后将这些结果与蒙特卡罗模拟结果进行比较。
不同体素化患者模型之间的剂量变化很小。取决于管电压和扫描仪以及患者模型，与蒙特卡罗模拟相比，CTDIvol 值高估了峰值皮肤剂量 26%-65%，高估了晶状体剂量 33%-106%。AAPM 第 111 号报告中的测量值更接近峰值皮肤估计值，低估了 14%，高估了 33%，晶状体剂量估计值低估了 9%，高估了 66%。与体素化模型模拟相比，ImPACT 电子表格高估了晶状体剂量 2%-82%。
CTDIvol 始终高估了晶状体和皮肤的剂量。ImPACT 工具也高估了晶状体剂量。因此，它们仍然可以作为 CT 神经灌注研究中剂量的保守预测指标。在本研究中使用的患者模型中，AAPM 第 111 号报告中的测量值比 CTDIvol 和 ImPACT 更能预测峰值皮肤和晶状体剂量。需要记住的是，AAPM 第 111 号峰值剂量指标和 CTDIvol 剂量指标都是剂量指标，并非旨在代表实际器官剂量。
