Yang Ming, Wohlfahrt Patrick, Shen Chenyang, Bouchard Hugo
The University of Texas MD Anderson Cancer Center, Department of Radiation Physics, 1515 Holcombe Blvd Houston, TX 77030, United States of America.
Massachusetts General Hospital and Harvard Medical School, Department of Radiation Oncology, Boston, MA 02115, United States of America.
Phys Med Biol. 2023 Feb 6;68(4). doi: 10.1088/1361-6560/acabfa.
Range uncertainty has been a key factor preventing particle radiotherapy from reaching its full physical potential. One of the main contributing sources is the uncertainty in estimating particle stopping power () within patients. Currently, thedistribution in a patient is derived from a single-energy CT (SECT) scan acquired for treatment planning by converting CT number expressed in Hounsfield units (HU) of each voxel tousing a Hounsfield look-up table (HLUT), also known as the CT calibration curve. HU andshare a linear relationship with electron density but differ in their additional dependence on elemental composition through different physical properties, i.e. effective atomic number and mean excitation energy, respectively. Because of that, the HLUT approach is particularly sensitive to differences in elemental composition between real human tissues and tissue surrogates as well as tissue variations within and among individual patients. The use of dual-energy CT (DECT) forprediction has been shown to be effective in reducing the uncertainty inestimation compared to SECT. The acquisition of CT data over different x-ray spectra yields additional information on the material elemental composition. Recently, multi-energy CT (MECT) has been explored to deduct material-specific information with higher dimensionality, which has the potential to further improve the accuracy ofestimation. Even though various DECT and MECT methods have been proposed and evaluated over the years, these approaches are still only scarcely implemented in routine clinical practice. In this topical review, we aim at accelerating this translation process by providing: (1) a comprehensive review of the existing DECT/MECT methods forestimation with their respective strengths and weaknesses; (2) a general review of uncertainties associated with DECT/MECT methods; (3) a general review of different aspects related to clinical implementation of DECT/MECT methods; (4) other potential advanced DECT/MECT applications beyondestimation.
射程不确定性一直是阻碍粒子放疗充分发挥其物理潜能的关键因素。主要促成因素之一是在患者体内估算粒子阻止本领（ ）时的不确定性。目前，患者体内的 分布是通过为治疗计划获取的单能CT（SECT）扫描得出的，方法是使用霍恩斯菲尔德查找表（HLUT，也称为CT校准曲线）将每个体素以亨氏单位（HU）表示的CT值转换为 。HU和 与电子密度呈线性关系，但由于分别通过不同的物理特性（即有效原子序数和平均激发能）对元素组成有额外的依赖性，二者有所不同。因此，HLUT方法对真实人体组织与组织替代物之间以及个体患者体内和个体患者之间的元素组成差异特别敏感。与SECT相比，使用双能CT（DECT）进行 预测已被证明可有效降低 估算中的不确定性。在不同X射线光谱上采集CT数据可提供有关材料元素组成的额外信息。最近，已探索使用多能CT（MECT）来推导具有更高维度的材料特定信息，这有可能进一步提高 估算的准确性。尽管多年来已经提出并评估了各种DECT和MECT方法，但这些方法在常规临床实践中的应用仍然很少。在本专题综述中，我们旨在通过提供以下内容来加速这一转化过程：（1）对现有的用于 估算的DECT/MECT方法进行全面综述，并阐述其各自的优缺点；（2）对与DECT/MECT方法相关的不确定性进行一般性综述；（3）对与DECT/MECT方法临床应用相关的不同方面进行一般性综述；（4）除 估算之外的其他潜在的先进DECT/MECT应用。
