Division of Diagnostic Imaging Physics and Webster Center for Advanced Research and Education in Radiation, Department of Radiology, Massachusetts General Hospital, Boston, Massachusetts 02114, USA.
Med Phys. 2013 Aug;40(8):081914. doi: 10.1118/1.4813899.
AAPM Task Group 111 proposed to measure the equilibrium dose-pitch product Deq for scan modes involving table translation and the midpoint dose DL(0) for stationary-table modes on the central and peripheral axes of sufficiently long (e.g., at least 40 cm) phantoms. This paper presents an alternative approach to calculate both metrics using the measurements of scanning the standard computed tomographic (CT) dosimetry phantoms on CT scanners.
Deq was calculated from CTDI100 and ε(CTDI100) (CTDI100 efficiency), and DL(0) was calculated from D̂eq and the approach to equilibrium function H(L) = DL(0)∕Deq, where Deq was the equilibrium dose. CTDI100 may be directly obtained from several sources (such as medical physicist's CT scanner performance evaluation or the IMPACT CT patient dosimetry calculator), or be derived from CTDIVol using the central to peripheral CTDI100 ratio (R100). The authors have provided the required ε(CTDI100) and H(L) data in two previous papers [X. Li, D. Zhang, and B. Liu, Med. Phys. 39, 901-905 (2012); and ibid. 40, 031903 (10pp.) (2013)]. R100 was assessed for a series of GE, Siemens, Philips, and Toshiba CT scanners with multiple settings of scan field of view, tube voltage, and bowtie filter.
The calculated DL(0) and DL(0)/Deq in PMMA and water cylinders were consistent with the measurements on two GE CT scanners (LightSpeed 16 and VCT) by Dixon and Ballard [Med. Phys. 34, 3399-3413 (2007)], the measurements on a Siemens CT scanner (SOMATOM Spirit Power) by Descamps et al. [J. Appl. Clin. Med. Phys. 13, 293-302 (2012)], and the Monte Carlo simulations by Boone [Med. Phys. 36, 4547-4554 (2009)].
Deq and DL(0) can be calculated using the alternative approach. The authors have provided the required ε(CTDI100) and H(L) data in two previous papers. R100 is presented for a majority of multidetector CT scanners currently on the market, and can be easily assessed for other CT scanners or operating conditions not covered in this study. The central to peripheral Deq ratio is about 1.50 and 1.12 times of R100 for the 32- and 16-cm diameter PMMA phantom, respectively.
AAPM 工作组 111 提议测量涉及台平移的扫描模式的平衡剂量-螺距乘积 Deq 和足够长（例如，至少 40cm）的模体中心和外周轴上的固定台模式的中点剂量 DL(0)。本文提出了一种使用 CT 扫描仪上标准 CT 剂量测定体模的扫描测量来计算这两个指标的替代方法。
Deq 由 CTDI100 和 ε(CTDI100)（CTDI100 效率）计算得出，DL(0) 由 D̂eq 和平衡函数 H(L) = DL(0)∕Deq 计算得出，其中 Deq 为平衡剂量。CTDI100 可直接从多个来源获得（例如，医学物理学家的 CT 扫描仪性能评估或 IMPACT CT 患者剂量计算器），或使用中央到外周 CTDI100 比（R100）从 CTDIVol 中得出。作者在之前的两篇论文中提供了所需的 ε(CTDI100)和 H(L)数据[X. Li、D. Zhang 和 B. Liu，医学物理学 39，901-905（2012 年）；同上，第 40 卷，031903（10 页）（2013 年）]。评估了一系列 GE、西门子、飞利浦和东芝 CT 扫描仪的 R100，这些扫描仪具有多种扫描视野、管电压和蝶形滤波器设置。
在 PMMA 和水圆柱体内计算得出的 DL(0)和 DL(0)/Deq 与 Dixon 和 Ballard[医学物理学 34，3399-3413（2007 年）]在两台 GE CT 扫描仪（LightSpeed 16 和 VCT）上的测量值、Descamps 等人[应用临床医学物理 13，293-302（2012 年）]在西门子 CT 扫描仪（SOMATOM Spirit Power）上的测量值以及 Boone[医学物理学 36，4547-4554（2009 年）]的蒙特卡罗模拟值一致。
可以使用替代方法计算 Deq 和 DL(0)。作者在之前的两篇论文中提供了所需的 ε(CTDI100)和 H(L)数据。本文给出了目前市场上大多数多排 CT 扫描仪的 R100，并可以轻松评估本研究中未涵盖的其他 CT 扫描仪或操作条件的 R100。32cm 和 16cm 直径 PMMA 体模的中心到外周 Deq 比值分别约为 R100 的 1.50 倍和 1.12 倍。
