Department of Radiotherapy, Medical University Vienna/AKH Wien, Austria.
Radiother Oncol. 2012 Aug;104(2):249-56. doi: 10.1016/j.radonc.2012.06.007. Epub 2012 Jul 17.
The aim of this work was to compare the accuracy of different HU adjustments for CBCT-based dose calculation.
Dose calculation was performed on CBCT images of 30 patients. In the first two approaches phantom-based (Pha-CC) and population-based (Pop-CC) conversion curves were used. The third method (WAB) represents override of the structures with standard densities for water, air and bone. In ROI mapping approach all structures were overridden with average HUs from planning CT. All techniques were benchmarked to the Pop-CC and CT-based plans by DVH comparison and γ-index analysis.
For prostate plans, WAB and ROI mapping compared to Pop-CC showed differences in PTV D(median) below 2%. The WAB and Pha-CC methods underestimated the bladder dose in IMRT plans. In lung cases PTV coverage was underestimated by Pha-CC method by 2.3% and slightly overestimated by the WAB and ROI techniques. The use of the Pha-CC method for head-neck IMRT plans resulted in difference in PTV coverage up to 5%. Dose calculation with WAB and ROI techniques showed better agreement with pCT than conversion curve-based approaches.
Density override techniques provide an accurate alternative to the conversion curve-based methods for dose calculation on CBCT images.
本研究旨在比较基于 CBCT 的剂量计算中不同 HU 调整的准确性。
对 30 例患者的 CBCT 图像进行了剂量计算。在前两种方法中，使用了基于体模（Pha-CC）和基于人群（Pop-CC）的转换曲线。第三种方法（WAB）代表用标准水、空气和骨密度覆盖结构。在 ROI 映射方法中，所有结构均被平均 CT 规划的 HUs 覆盖。所有技术均通过 DVH 比较和γ指数分析与 Pop-CC 和 CT 计划进行基准测试。
对于前列腺计划，与 Pop-CC 相比，WAB 和 ROI 映射在 PTV D（中位数）方面的差异低于 2%。WAB 和 Pha-CC 方法低估了 IMRT 计划中的膀胱剂量。在肺部病例中，Pha-CC 方法低估了 PTV 覆盖度 2.3%，而 WAB 和 ROI 技术则略有高估。对于头颈部 IMRT 计划，使用 Pha-CC 方法会导致 PTV 覆盖度差异高达 5%。与转换曲线方法相比，WAB 和 ROI 技术的剂量计算与 pCT 具有更好的一致性。
密度覆盖技术为基于 CBCT 图像的剂量计算提供了一种比转换曲线方法更准确的替代方法。
