Novel methods of measuring single scan dose profiles and cumulative dose in CT.
Novel methods of measuring single scan dose profiles and cumulative dose in CT.
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测量 CT 中单次扫描剂量分布和累积剂量的新方法。
DOI：
10.1118/1.1835571
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发表时间：
2004
期刊：
影响因子：
3.8
通讯作者：
S. Rathee
中科院分区：
文献类型：
--
作者：
K. Nakonechny;B. Fallone;S. Rathee
计算机断层扫描剂量指数（CTDI）是CT研究中患者剂量的常规指标。通过使用100 mm长的铅笔电离室和单轴扫描，将其测量为纵向单扫描剂量分布（SSDP）的积分。然而，假设大部分SSDP包含在腔室长度内，即使对于薄片也可能无效。我们已经测量了几个切片宽度的SSDP的两个CT扫描仪使用PTW钻石探测器放置在一个300 mm × 200 mm × 300 mm的水当量塑料体模。还使用氟化锂（LiF）TLD和IC-10小体积离子室测量了一个SSDP，验证了使用金刚石检测器测量的SSDP的一般形状。还使用标准圆柱形PMMA CT体模（140 mm长）来定性研究体模形状、长度和组成对测量的SSDP的影响。在水等效体模中用金刚石探测器测量的SSDP被数值积分，以计算在各种扫描长度L的中心处的相对累积剂量D（L）（0）计算。D（L）（0）calc在L > 300 mm时达到平衡值，表明需要比标准CT剂量体模更长的体模。我们还测量了绝对累积剂量使用IC-10小体积离子室，D（L）（0）SV，在三个点的几个束宽和扫描长度的体模横截面。对于一个CT系统，在轴向和螺旋扫描模式下进行这些测量。使用102 mm有效长度的笔式电离室测量的绝对CTDI 100在使用L约100 mm的小体积离子室测量的D（L）（0）SV的4%范围内，表明非笔式电离室可成功用于CT剂量测定。对于标称射束宽度范围为3 - 20 mm且L约为250 mm的情况，水等效体模椭圆形横截面中心处的D（L）（0）SV值比实测CTDI 100高约25%-30%。对于小波束宽度，L约250 mm和L约14 x波束宽度（CTDI 14 nT）的D（L）（0）SV差异高达50%。对于L约250 mm，沿体模主轴沿着70 mm深度处的外周点剂量比L约100 mm高22%。L约250 mm的CTDI 100和D（L）（0）SV之间的差异与从测量的SSDP的数值积分中得出的预测一致。由于在标准CT体模的长度之外测量的剂量相当大，因此应在较长的体模中进行较长身体扫描系列的CT剂量测定。如我们所示，可以进行测量，使用小体积腔室，使用多次扫描平移通过光束。
Computed tomography dose index (CTDI) is a conventional indicator of the patient dose in CT studies. It is measured as the integration of the longitudinal single scan dose profile (SSDP) by using a 100-mm-long pencil ionization chamber and a single axial scan. However, the assumption that most of the SSDP is contained within the chamber length may not be valid even for thin slices. We have measured the SSDPs for several slice widths on two CT scanners using a PTW diamond detector placed in a 300 mm x 200 mm x 300 mm water-equivalent plastic phantom. One SSDP was also measured using lithium fluoride (LiF) TLDs and an IC-10 small volume ion chamber, verifying the general shape of the SSDP measured using the diamond detector. Standard cylindrical PMMA CT phantoms (140 mm length) were also used to qualitatively study the effects of phantom shape, length, and composition on the measured SSDP. The SSDPs measured with the diamond detector in the water-equivalent phantom were numerically integrated to calculate the relative accumulated dose D(L)(0)calc at the center of various scan lengths L. D(L)(0)calc reached an equilibrium value for L > 300 mm, suggesting the need for phantoms longer than standard CT dose phantoms. We have also measured the absolute accumulated dose using an IC-10 small volume ion chamber, D(L)(0)SV, at three points in the phantom cross section for several beamwidths and scan lengths. For one CT system, these measurements were made in both axial and helical scanning modes. The absolute CTDI100, measured with a 102 mm active length pencil chamber, were within 4% of D(L)(0)SV measured with the small volume ion chamber for L approximately 100 mm suggesting that nonpencil chambers can be successfully used for CT dosimetry. For nominal beam widths ranging from 3 to 20 mm and for L approximately 250 mm, D(L)(0)SV values at the center of the water-equivalent phantom's elliptic cross section were approximately 25%-30% higher than the measured CTDI100. For small beamwidths, the difference in D(L)(0)SV for L approximately 250 mm and L approximately 14 x beamwidth (CTDI14nT) reached up to 50%. Peripheral point doses at 70 mm depth along the major axis of the phantom for L approximately 250 mm were up to 22% higher than for L approximately 100 mm. The differences between CTDI100 and D(L)(0)SV for L approximately 250 mm were in good agreement with the predictions made from the numerical integration of the measured SSDPs. Due to the considerable dose measured beyond the length of standard CT phantoms, CT dosimetry for longer body scan series should be performed in longer phantoms. Measurements could be made as we have shown, using a small volume chamber translating through the beam using multiple scans.
蒙特卡罗评估扫描体积附近组织的计算机断层扫描剂量。
影响因子：
3.8
作者：
Boone,JM;Cooper3rd,VN;Nemzek,WR;McGahan,JP;Seibert,JA
通讯作者：
Seibert,JA