Almatani Turki, Hugtenburg Richard P, Lewis Ryan D, Barley Susan E, Edwards Mark A
1 College of Medicine, Swansea University, Swansea, UK.
2 Department of Medical Physics and Clinical Engineering, Singleton Hospital, ABM University Health Board, Swansea, UK.
Br J Radiol. 2016 Oct;89(1066):20160443. doi: 10.1259/bjr.20160443. Epub 2016 Jul 27.
Cone beam CT (CBCT) images contain more scatter than a conventional CT image and therefore provide inaccurate Hounsfield units (HUs). Consequently, CBCT images cannot be used directly for radiotherapy dose calculation. The aim of this study is to enable dose calculations to be performed with the use of CBCT images taken during radiotherapy and evaluate the necessity of replanning.
A patient with prostate cancer with bilateral metallic prosthetic hip replacements was imaged using both CT and CBCT. The multilevel threshold (MLT) algorithm was used to categorize pixel values in the CBCT images into segments of homogeneous HU. The variation in HU with position in the CBCT images was taken into consideration. This segmentation method relies on the operator dividing the CBCT data into a set of volumes where the variation in the relationship between pixel values and HUs is small. An automated MLT algorithm was developed to reduce the operator time associated with the process. An intensity-modulated radiation therapy plan was generated from CT images of the patient. The plan was then copied to the segmented CBCT (sCBCT) data sets with identical settings, and the doses were recalculated and compared.
Gamma evaluation showed that the percentage of points in the rectum with γ < 1 (3%/3 mm) were 98.7% and 97.7% in the sCBCT using MLT and the automated MLT algorithms, respectively. Compared with the planning CT (pCT) plan, the MLT algorithm showed -0.46% dose difference with 8 h operator time while the automated MLT algorithm showed -1.3%, which are both considered to be clinically acceptable, when using collapsed cone algorithm.
The segmentation of CBCT images using the method in this study can be used for dose calculation. For a patient with prostate cancer with bilateral hip prostheses and the associated issues with CT imaging, the MLT algorithms achieved a sufficient dose calculation accuracy that is clinically acceptable. The automated MLT algorithm reduced the operator time associated with implementing the MLT algorithm to achieve clinically acceptable accuracy. This saved time makes the automated MLT algorithm superior and easier to implement in the clinical setting.
The MLT algorithm has been extended to the complex example of a patient with bilateral hip prostheses, which with the introduction of automation is feasible for use in adaptive radiotherapy, as an alternative to obtaining a new pCT and reoutlining the structures.
锥形束CT（CBCT）图像比传统CT图像包含更多散射，因此提供的亨氏单位（HU）不准确。因此，CBCT图像不能直接用于放射治疗剂量计算。本研究的目的是能够使用放射治疗期间采集的CBCT图像进行剂量计算，并评估重新计划的必要性。
对一名患有双侧金属人工髋关节置换的前列腺癌患者进行CT和CBCT成像。使用多级阈值（MLT）算法将CBCT图像中的像素值分类为均匀HU段。考虑了CBCT图像中HU随位置的变化。这种分割方法依赖于操作员将CBCT数据划分为一组体积，其中像素值与HU之间关系的变化很小。开发了一种自动MLT算法以减少与该过程相关的操作员时间。根据患者的CT图像生成调强放射治疗计划。然后将该计划以相同设置复制到分割后的CBCT（sCBCT）数据集，并重新计算和比较剂量。
伽马评估显示，在使用MLT和自动MLT算法的sCBCT中，直肠中γ<1（3%/3毫米）的点的百分比分别为98.7%和97.7%。与计划CT（pCT）计划相比，使用坍缩圆锥算法时，MLT算法显示剂量差异为-0.46%，操作员时间为8小时，而自动MLT算法显示剂量差异为-1.3%，两者均被认为在临床上可接受。
使用本研究中的方法对CBCT图像进行分割可用于剂量计算。对于患有双侧髋关节假体的前列腺癌患者以及与CT成像相关的问题，MLT算法实现了临床上可接受的足够剂量计算精度。自动MLT算法减少了与实施MLT算法相关的操作员时间，以实现临床上可接受的精度。这种节省的时间使得自动MLT算法更优越，并且在临床环境中更易于实施。
MLT算法已扩展到双侧髋关节假体患者的复杂示例，随着自动化的引入，它可用于自适应放射治疗，作为获取新的pCT并重新勾勒结构的替代方法。
