Development of a CT number calibration audit phantom in photon radiation therapy: A pilot study
Development of a CT number calibration audit phantom in photon radiation therapy: A pilot study
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光子放射治疗中 CT 数校准审核模型的开发：一项试点研究
DOI：
10.1002/mp.14077
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发表时间：
2020
期刊：
影响因子：
3.8
通讯作者：
Nagata Yasushi
中科院分区：
文献类型：
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作者：
Nakao Minoru;Ozawa Shuichi;Miura Hideharu;Yamada Kiyoshi;Habara Kosaku;Hayata Masahiro;Kusaba Hayate;Kawahara Daisuke;Miki Kentaro;Nakashima Takeo;Ochi Yusuke;Tsuda Shintaro;Seido Mineaki;Morimoto Yoshiharu;Kawakubo Atsushi;Nozaki Hiroshige;Nagata Yasushi
在光子放射治疗中，计算机断层扫描（CT）的数值被转换成质量密度（MD）或相对电子密度（RED）的值。CT‐MD或CT‐RED校准表与非均匀介质中的人体剂量计算相关。CT‐MD或CT‐RED校准表受患者成像（CT扫描仪制造商、扫描参数和患者体型）、校准过程（组织等效体模制造商和组织等效材料的选择）、组织等效材料和标准组织之间的差异以及所应用的剂量计算算法的影响;但是，尚未建立CT编号校准审核。本研究的目的是开发一个邮政审计幻影，并建立一个CT数校准audit process.MethodsA传统的化学计量校准进行最小二乘拟合的MD，材料重量和测量的CT数之间的关系，使用两个参数。在这项研究中，一个新的化学计量CT数校准方案已经验建立，使用三个参数，以协调计算的CT数与测量的CT数的空气和肺组织。此外，合适的材料集和化学计量CT数校准所需的材料的最小数量被确定。使用来自国际放射防护委员会出版物110的MD和元素重量作为标准组织数据，以生成CT‐MD和CT‐RED校准表。一个小尺寸的，CT数校准体模开发的邮政审计，和化学计量CT数校准体模进行了比较，在放射治疗计划系统（RTPS）与五个放射治疗institutions.ResultsWhen一个最小二乘拟合进行化学计量CT数校准与三个参数，计算的CT值与测量的CT值具有更好的一致性。我们只使用两种材料建立了化学计量CT数校准，因为该过程的准确性不是由所用材料的数量而是由所含元素的数量决定的。化学计量CT数校准与组织替代物校准相当，剂量差异小于1%。CT数校准审计的大纲被证明通过多机构study.ConclusionsWe建立了一个新的化学计量CT数校准方法，用于验证RTPS中注册的CT数校准表。我们还开发了一种用于邮政审计的CT数字校准体模，并通过位于几个机构的多台CT扫描仪的性能进行了验证。新的化学计量CT数校准具有仅使用两种材料进行的优点，并且减小了空气和肺组织的计算CT数与测量CT数之间的差异。将来，使用更小的体模可能实现邮政CT编号校准审核。
PurposeIn photon radiation therapy, computed tomography (CT) numbers are converted into values for mass density (MD) or relative electron density to water (RED). CT‐MD or CT‐RED calibration tables are relevant for human body dose calculation in an inhomogeneous medium. CT‐MD or CT‐RED calibration tables are influenced by patient imaging (CT scanner manufacturer, scanning parameters, and patient size), the calibration process (tissue‐equivalent phantom manufacturer, and selection of tissue‐equivalent material), differences between tissue‐equivalent materials and standard tissues, and the dose calculation algorithm applied; however, a CT number calibration audit has not been established. The purposes of this study were to develop a postal audit phantom, and to establish a CT number calibration audit process.MethodsA conventional stoichiometric calibration conducts a least square fit of the relationships between the MD, material weight, and measured CT number, using two parameters. In this study, a new stoichiometric CT number calibration scheme has been empirically established, using three parameters to harmonize the calculated CT number with the measured CT number for air and lung tissue. In addition, the suitable material set and the minimal number of materials required for stoichiometric CT number calibration were determined. The MDs and elemental weights from the International Commission on Radiological Protection Publication 110 were used as standard tissue data, to generate the CT‐MD and CT‐RED calibration tables. A small‐sized, CT number calibration phantom was developed for a postal audit, and stoichiometric CT number calibration with the phantom was compared to the CT number calibration tables registered in the radiotherapy treatment planning systems (RTPSs) associated with five radiotherapy institutions.ResultsWhen a least square fit was performed for the stoichiometric CT number calibration with the three parameters, the calculated CT number showed better agreement with the measured CT number. We established stoichiometric CT number calibration using only two materials because the accuracy of the process was determined not by the number of used materials but by the number of elements contained. The stoichiometric CT number calibration was comparable to the tissue‐substitute calibration, with a dose difference less than 1%. An outline of the CT number calibration audit was demonstrated through a multi‐institutional study.ConclusionsWe established a new stoichiometric CT number calibration method for validating the CT number calibration tables registered in RTPSs. We also developed a CT number calibration phantom for a postal audit, which was verified by the performances of multiple CT scanners located at several institutions. The new stoichiometric CT number calibration has the advantages of being performed using only two materials, and decreasing the difference between the calculated and measured CT numbers for air and lung tissue. In the future, a postal CT number calibration audit might be achievable using a smaller phantom.