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.
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; Faculty of Medicine and Public Health, HRH Princess Chulabhorn College of Medical Science, Chulabhorn Royal Academy, Bangkok, Thailand.
Int J Radiat Oncol Biol Phys. 2021 Nov 15;111(4):1033-1043. doi: 10.1016/j.ijrobp.2021.06.036. Epub 2021 Jul 3.
Uncertainty in computed tomography (CT)-based range prediction substantially impairs the accuracy of proton therapy. Direct determination of the stopping-power ratio (SPR) from dual-energy CT (DECT) has been proposed (DirectSPR), and initial validation studies in phantoms and biological tissues have proven a high accuracy. However, a thorough validation of range prediction in patients has not yet been achieved by any means. Here, we present the first systematic validation of CT-based proton range prediction in patients using prompt gamma imaging (PGI).
A PGI slit camera system with improved positioning accuracy, using a floor-based docking station, was used. Its overall uncertainty for range prediction validation was determined experimentally with both x-ray and beam measurements. The accuracy of range prediction in patients was determined from clinical PGI measurements during hypofractionated treatment of 5 patients with prostate cancer - in total 30 fractions with in-room control-CTs. For each pencil-beam-scanning spot, the range shift was obtained by comparing the PGI measurement to a control-CT-based PGI simulation. Three different SPR prediction approaches were applied in simulations: a standard CT-number-to-SPR conversion (Hounsfield look-up table [HLUT]), an adapted HLUT (DECT optimized), and DirectSPR. The spot-wise weighted mean range shift from all spots served as a measure for the accuracy of the respective range prediction approach.
A mean range prediction accuracy of 0.0% ± 0.5%, 0.3% ± 0.4%, and 1.8% ± 0.4% was obtained for DirectSPR, adapted HLUT, and standard HLUT, respectively. The overall validation uncertainty of the second-generation PGI slit camera is about 1 mm (2σ) for all approaches, which is smaller than the range prediction uncertainty for deep-seated tumors.
For the first time, range prediction accuracy was assessed in clinical routine using PGI range verification in prostate cancer treatments. Both DECT-derived range prediction approaches agree well with the measured proton range from PGI verification, whereas the standard HLUT approach differs relevantly. These results endorse the recent reduction of clinical safety margins in DirectSPR-based treatment planning in our institution.
基于计算机断层扫描（CT）的射程预测的不确定性极大地降低了质子治疗的准确性。已经提出了从双能 CT（DECT）直接确定阻止本领比（SPR）的方法（DirectSPR），并且已经在体模和生物组织中的初步验证研究证明了其具有很高的准确性。但是，迄今为止，还没有任何方法能够彻底验证患者的射程预测。在这里，我们使用瞬发伽马成像（PGI）首次系统地验证了基于 CT 的质子在患者中的射程预测。
使用改进的定位精度的 PGI 狭缝相机系统，使用基于地面的对接站。使用 X 射线和光束测量对其进行了实验确定，以确定其进行射程预测验证的总不确定性。使用前列腺癌 5 例患者的分次治疗期间的临床 PGI 测量来确定患者中的射程预测的准确性-总共进行了 30 次，每次治疗都有室内控制 CT。对于每个铅笔束扫描点，通过将 PGI 测量值与基于控制 CT 的 PGI 模拟进行比较来获得射程偏移量。在模拟中应用了三种不同的 SPR 预测方法：标准 CT 数到 SPR 的转换（Hounsfield 查找表[HLUT]），经过调整的 HLUT（DECT 优化）和 DirectSPR。所有点的加权平均射程偏移量作为各自射程预测方法的准确性的度量。
对于 DirectSPR，经过调整的 HLUT 和标准 HLUT，分别获得了 0.0%±0.5%，0.3%±0.4%和 1.8%±0.4%的平均射程预测精度。第二代 PGI 狭缝相机的整体验证不确定性对于所有方法均约为 1mm（2σ），对于深部肿瘤的射程预测不确定性较小。
这是首次使用前列腺癌治疗中的 PGI 射程验证来评估临床常规中的射程预测准确性。两种 DECT 衍生的射程预测方法均与 PGI 验证的实测质子射程吻合良好，而标准 HLUT 方法则存在明显差异。这些结果支持了我们机构中基于 DirectSPR 的治疗计划中最近减少临床安全裕度的做法。
