Center for Image Sciences, Universitair Medisch Centrum Utrecht, Utrecht, Netherlands.
Phys Med Biol. 2017 Nov 21;62(24):9159-9176. doi: 10.1088/1361-6560/aa9677.
A magnetic resonance (MR)-only radiotherapy workflow can reduce cost, radiation exposure and uncertainties introduced by CT-MRI registration. A crucial prerequisite is generating the so called pseudo-CT (pCT) images for accurate dose calculation and planning. Many pCT generation methods have been proposed in the scope of photon radiotherapy. This work aims at verifying for the first time whether a commercially available photon-oriented pCT generation method can be employed for accurate intensity-modulated proton therapy (IMPT) dose calculation. A retrospective study was conducted on ten prostate cancer patients. For pCT generation from MR images, a commercial solution for creating bulk-assigned pCTs, called MR for Attenuation Correction (MRCAT), was employed. The assigned pseudo-Hounsfield Unit (HU) values were adapted to yield an increased agreement to the reference CT in terms of proton range. Internal air cavities were copied from the CT to minimise inter-scan differences. CT- and MRCAT-based dose calculations for opposing beam IMPT plans were compared by gamma analysis and evaluation of clinically relevant target and organ at risk dose volume histogram (DVH) parameters. The proton range in beam's eye view (BEV) was compared using single field uniform dose (SFUD) plans. On average, a [Formula: see text] mm) gamma pass rate of 98.4% was obtained using a [Formula: see text] dose threshold after adaptation of the pseudo-HU values. Mean differences between CT- and MRCAT-based dose in the DVH parameters were below 1 Gy ([Formula: see text]). The median proton range difference was [Formula: see text] mm, with on average 96% of all BEV dose profiles showing a range agreement better than 3 mm. Results suggest that accurate MR-based proton dose calculation using an automatic commercial bulk-assignment pCT generation method, originally designed for photon radiotherapy, is feasible following adaptation of the assigned pseudo-HU values.
磁共振（MR）仅放疗工作流程可以降低成本、辐射暴露和 CT-MRI 配准带来的不确定性。一个关键的前提是生成所谓的伪 CT（pCT）图像，以便进行准确的剂量计算和规划。在光子放疗范围内已经提出了许多 pCT 生成方法。这项工作旨在首次验证一种商用的光子定向 pCT 生成方法是否可用于精确的强度调制质子治疗（IMPT）剂量计算。对十名前列腺癌患者进行了回顾性研究。对于从 MR 图像生成 pCT，使用了一种用于创建批量分配 pCT 的商业解决方案，称为用于衰减校正的 MR（MRCAT）。分配的伪亨氏单位（HU）值经过调整，以在质子射程方面与参考 CT 更一致。内部空气腔从 CT 复制以最大程度地减少扫描间差异。通过伽马分析和评估临床相关靶区和危及器官剂量体积直方图（DVH）参数，比较了基于 CT 和 MRCAT 的对向束 IMPT 计划的剂量计算。使用单野均匀剂量（SFUD）计划比较了射束视线（BEV）中的质子射程。经伪 HU 值调整后，平均获得[Formula: see text]毫米）伽马通过率为 98.4%，使用[Formula: see text]剂量阈值。DVH 参数中 CT 和 MRCAT 基础剂量的平均差异低于 1 Gy（[Formula: see text]）。质子范围中位数差异为[Formula: see text]毫米，平均 96%的所有 BEV 剂量曲线显示范围一致性优于 3 毫米。结果表明，使用自动商用批量分配 pCT 生成方法进行准确的基于 MR 的质子剂量计算是可行的，前提是调整分配的伪 HU 值。
