Reidel Claire-Anne, Horst Felix, Schuy Christoph, Jäkel Oliver, Ecker Swantje, Henkner Katrin, Brons Stephan, Durante Marco, Weber Uli
Biophysics Department, GSI Helmholtzzentrum für Schwerionenforschung GmbH, Darmstadt, Germany.
Division of Medical Physics in Radiation Oncology, German Cancer Research Center (DKFZ), Heidelberg, Germany.
Front Oncol. 2022 Mar 25;12:830080. doi: 10.3389/fonc.2022.830080. eCollection 2022.
Fiducial markers are used for image guidance to verify the correct positioning of the target for the case of tumors that can suffer interfractional motion during proton therapy. The markers should be visible on daily imaging, but at the same time, they should produce minimal streak artifacts in the CT scans for treatment planning and induce only slight dose perturbations during particle therapy. In this work, these three criteria were experimentally investigated at the Heidelberg Ion Beam Therapy Center. Several small fiducial markers with different geometries and materials (gold, platinum, and carbon-coated ZrO) were evaluated. The streak artifacts on treatment planning CT were measured with and without iMAR correction, showing significantly smaller artifacts from markers lighter than 6 mg and a clear improvement with iMAR correction. Daily imaging as X-ray projections and in-room mobile CT were also performed. Markers heavier than 6 mg showed a better contrast in the X-ray projections, whereas on the images from the in-room mobile CT, all markers were clearly visible. In the other part of this work, fluence perturbations of proton beams were measured for the same markers by using a tracker system of several high spatial resolution CMOS pixel sensors. The measurements were performed for single-energy beams, as well as for a spread-out Bragg peak. Three-dimensional fluence distributions were computed after reconstructing all particle trajectories. These measurements clearly showed that the ZrO markers and the low-mass gold/platinum markers (0.35mm diameter) induce perturbations being 2-3 times lower than the heavier gold or platinum markers of 0.5mm diameter. Monte Carlo simulations, using the FLUKA code, were used to compute dose distributions and showed good agreement with the experimental data after adjusting the phase space of the simulated proton beam compared to the experimental beam.
在质子治疗过程中，对于可能发生分次间运动的肿瘤病例， fiducial标记物用于图像引导以验证靶区的正确定位。这些标记物应在每日成像中可见，但同时，它们在用于治疗计划的CT扫描中应产生最小的条纹伪影，并且在粒子治疗期间仅引起轻微的剂量扰动。在这项工作中，在海德堡离子束治疗中心对这三个标准进行了实验研究。评估了几种具有不同几何形状和材料（金、铂和碳涂层ZrO）的小型fiducial标记物。在有和没有迭代金属伪影校正（iMAR）的情况下，测量了治疗计划CT上的条纹伪影，结果显示重量小于6mg的标记物产生的伪影明显更小，并且iMAR校正有明显改善。还进行了作为X射线投影的每日成像和室内移动CT成像。重量超过6mg的标记物在X射线投影中显示出更好的对比度，而在室内移动CT的图像上，所有标记物都清晰可见。在这项工作的另一部分中，通过使用由几个高空间分辨率CMOS像素传感器组成的跟踪系统，测量了相同标记物对质子束的注量扰动。对单能束以及扩展布拉格峰进行了测量。在重建所有粒子轨迹后，计算了三维注量分布。这些测量清楚地表明，ZrO标记物和低质量的金/铂标记物（直径0.35mm）引起的扰动比直径0.5mm的较重金或铂标记物低2至3倍。使用FLUKA代码进行的蒙特卡罗模拟用于计算剂量分布，并且在将模拟质子束的相空间与实验束进行调整后，与实验数据显示出良好的一致性。
