Calibration and error analysis of metal-oxide-semiconductor field-effect transistor dosimeters for computed tomography radiation dosimetry.
Calibration and error analysis of metal-oxide-semiconductor field-effect transistor dosimeters for computed tomography radiation dosimetry.
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DOI：
10.1002/mp.12592
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发表时间：
2017-12
期刊：
影响因子：
3.8
通讯作者：
Einstein AJ
中科院分区：
文献类型：
--
作者：
Trattner S;Prinsen P;Wiegert J;Gerland EL;Shefer E;Morton T;Thompson CM;Yagil Y;Cheng B;Jambawalikar S;Al-Senan R;Amurao M;Halliburton SS;Einstein AJ
金属氧化物半导体场效应晶体管（MOSFET）作为器官辐射剂量测定的有用工具，其在计算机断层扫描（CT）中的应用越来越多。虽然不同的方法已被用于MOSFET校准，那些使用常用的100毫米铅笔电离室没有纳入整个长度进行测量，此外，没有以前的工作已经严格评估了MOSFET校准中涉及的多个误差源。在本文中，我们提出了一种新的MOSFET校准方法，MOSFET电压测量转换为吸收剂量从CT，在整个长度的100 mm电离室进行的串行测量的基础上，并进行MOSFET电压测量的误差和四个来源的误差校准分析。MOSFET校准在两个地点进行，以确定管电位为80，100和120 kVp的单一校准因子，使用100 mm长的铅笔离子室和圆柱形计算机断层扫描剂量指数（CTDI）的32厘米直径的幻影。沿100 mm离子室轴的剂量分布沿着由CTDI体模的九个孔中的九个MOSFET以5 mm间隔采样。吸收剂量的方差被建模为MOSFET电压测量方差和校准因子方差之和，后者由三个主要子分量组成：电离室阅读方差、MOSFET到MOSFET的方差以及与以下事实相关的贡献：将少数MOSFET的平均校准因子用作所有MOSFET的平均值的估计。MOSFET电压测量误差估计的基础上重复测量的集合。根据上述分析计算校准因子总电压测量误差。确定的校准因子接近文献和制造商报告的校准因子（± 3 mV/mGy），范围为2.87 - 3.13 mV/mGy。MOSFET电压测量的误差σV与电压V的平方根成正比： 其中c = 0.11 mV。校准因子误差的主要贡献者是电离室阅读误差，误差为5%。对所有MOSFET使用单个校准因子会引入约5- 7%的额外误差，具体取决于用于确定单个校准因子的MOSFET数量。高剂量区域（± 30 mGy）的预期总体误差估计约为8%，而进行单独MOSFET校准时的预期总体误差为6%。对于低剂量区域（≤ 3 mGy），这些值分别为13%和12%。MOSFET校准方法的开发使用100 mm的铅笔离子室和CTDI体模，伴随着吸收剂量误差分析，反映了多个测量误差源。当使用单个校准因子时，每个管电位，对于不同的MOSFET，只有一个小的误差被引入到吸收剂量测定中，因此支持在涉及许多MOSFET的实验中使用这样的校准因子，例如那些需要准确估计辐射有效剂量的实验。
Metal-oxide-semiconductor field-effect transistors (MOSFETs) serve as a helpful tool for organ radiation dosimetry, and their use has grown in computed tomography (CT). While different approaches have been used for MOSFET calibration, those using the commonly-available 100 mm pencil ionization chamber have not incorporated measurements performed throughout its length, and moreover no previous work has rigorously evaluated the multiple sources of error involved in MOSFET calibration. In this paper we propose a new MOSFET calibration approach to translate MOSFET voltage measurements into absorbed dose from CT, based on serial measurements performed throughout the length of a 100 mm ionization chamber, and perform an analysis of the errors of MOSFET voltage measurements and four sources of error in calibration. MOSFET calibration was performed at two sites, to determine single calibration factors for tube potentials of 80, 100, and 120 kVp, using a 100 mm long pencil ion chamber and a cylindrical computed tomography dose index (CTDI) phantom of 32 cm diameter. The dose profile along the 100 mm ion chamber axis was sampled in 5 mm intervals by nine MOSFETs in the nine holes of the CTDI phantom. Variance of the absorbed dose was modeled as a sum of the MOSFET voltage measurement variance and the calibration factor variance, the latter being comprised of three main subcomponents: ionization chamber reading variance, MOSFET-to-MOSFET variation and a contribution related to the fact that the average calibration factor of a few MOSFETs was used as an estimate for the average value of all MOSFETs. MOSFET voltage measurement error was estimated based on sets of repeated measurements. The calibration factor overall voltage measurement error was calculated from the above analysis. Calibration factors determined were close to those reported in the literature and by the manufacturer (∼ 3mV/mGy), ranging from 2.87 to 3.13 mV/mGy. The error σV of a MOSFET voltage measurement was shown to be proportional to the square root of the voltage V: where c = 0.11 mV. A main contributor to the error in the calibration factor was the ionization chamber reading error with 5% error. The usage of a single calibration factor for all MOSFETs introduced an additional error of about 5-7%, depending on the number of MOSFETs that were used to determine the single calibration factor. The expected overall error in a high dose region (∼30 mGy) was estimated to be about 8%, compared to 6% when an individual MOSFET calibration was performed. For a low-dose region (∼3 mGy) these values were 13% and 12%. A MOSFET calibration method was developed using a 100 mm pencil ion chamber and a CTDI phantom, accompanied by an absorbed dose error analysis reflecting multiple sources of measurement error. When using a single calibration factor, per tube potential, for different MOSFETs, only a small error was introduced into absorbed dose determinations, thus supporting the use of such a calibration factor for experiments involving many MOSFETs, such as those required to accurately estimate radiation effective dose.
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