OncoRay - National Center for Radiation Research in Oncology, Faculty of Medicine and University Hospital Carl Gustav Carus, Technische Universität Dresden, Helmholtz-Zentrum Dresden-Rossendorf, Dresden, Germany.
Helmholtz-Zentrum Dresden-Rossendorf, Institute of Radiooncology - OncoRay, Dresden, Germany.
Med Phys. 2020 Apr;47(4):1796-1806. doi: 10.1002/mp.14085. Epub 2020 Feb 29.
Proton treatment planning relies on an accurate determination of stopping-power ratio (SPR) from x-ray computed tomography (CT). A refinement of the heuristic CT-based SPR prediction using a state-of-the-art Hounsfield look-up table (HLUT) is proposed, which incorporates patient SPR information obtained from dual-energy CT (DECT) in a retrospective patient-cohort analysis.
SPR datasets of 25 brain-tumor patients, 25 prostate-cancer patients, and three nonsmall cell lung-cancer (NSCLC) patients were calculated from clinical DECT scans with the comprehensively validated DirectSPR approach. Based on the median frequency distribution of voxelwise correlations between CT number and SPR within the irradiated volume, a piecewise linear function was specified (DirectSPR-based adapted HLUT). Differences in dose distribution and proton range were assessed for the nonadapted and adapted HLUT in comparison to the DirectSPR method, which has been shown to be an accurate and reliable SPR estimation method.
The application of the DirectSPR-based adapted HLUT instead of the nonadapted HLUT reduced the systematic proton range differences from 1.2% (1.1 mm) to -0.1% (0.0 mm) for brain-tumor patients, 1.7% (4.1 mm) to 0.2% (0.5 mm) for prostate-cancer patients, and 2.0% (2.9 mm) to -0.1% (0.0 mm) for NSCLC patients. Due to the large intra- and inter-patient tissue variability, range differences to DirectSPR larger than 1% remained for the adapted HLUT.
The incorporation of patient-specific correlations between CT number and SPR, derived from a retrospective application of DirectSPR to a broad patient cohort, improves the SPR accuracy of the current state-of-the-art HLUT approach. The DirectSPR-based adapted HLUT has been clinically implemented at the University Proton Therapy Dresden (Dresden, Germany) in 2017. This already facilitates the benefits of an improved DECT-based tissue differentiation within clinical routine without changing the general approach for range prediction (HLUT), and represents a further step toward full integration of the DECT-based DirectSPR method for treatment planning in proton therapy.
质子治疗计划依赖于从 X 射线计算机断层扫描（CT）准确确定阻止本领比（SPR）。本研究提出了一种基于最先进的亨氏单位查找表（HLUT）的启发式 CT 预测 SPR 的改进方法，该方法在回顾性患者队列分析中结合了从双能 CT（DECT）获得的患者 SPR 信息。
使用经过全面验证的 DirectSPR 方法，从 25 例脑肿瘤患者、25 例前列腺癌患者和 3 例非小细胞肺癌（NSCLC）患者的临床 DECT 扫描中计算 SPR 数据集。基于受照体积内 CT 数与 SPR 的体素级相关的中位数频率分布，指定了一个分段线性函数（基于 DirectSPR 的自适应 HLUT）。与已被证明是一种准确可靠的 SPR 估计方法的 DirectSPR 方法相比，比较了非自适应和自适应 HLUT 对剂量分布和质子射程的影响。
与非自适应 HLUT 相比，应用基于 DirectSPR 的自适应 HLUT 可将脑肿瘤患者的质子射程系统差异从 1.2%（1.1mm）降低至-0.1%（0.0mm），将前列腺癌患者的质子射程系统差异从 1.7%（4.1mm）降低至 0.2%（0.5mm），将 NSCLC 患者的质子射程系统差异从 2.0%（2.9mm）降低至-0.1%（0.0mm）。由于组织内和组织间的个体变异较大，对于自适应 HLUT，与 DirectSPR 的差异仍大于 1%。
从 DirectSPR 在广泛的患者队列中的回顾性应用中得出 CT 数与 SPR 之间的患者特异性相关性，并将其纳入当前最先进的 HLUT 方法中，可提高 SPR 的准确性。基于 DirectSPR 的自适应 HLUT 已于 2017 年在德国德累斯顿质子治疗中心（德国德累斯顿）临床实施。这已经促进了在临床常规中基于改进的 DECT 进行组织分化的优势，而无需改变用于射程预测（HLUT）的一般方法，并且是朝着质子治疗中完全集成基于 DECT 的 DirectSPR 方法的治疗计划的又一步。
