Maspero Matteo, Tyyger Marcus D, Tijssen Rob H N, Seevinck Peter R, Intven Martijn P W, van den Berg Cornelis A T
Department of Radiotherapy, Universitair Medisch Centrum Utrecht, The Netherlands.
Center for Image Sciences, Universitair Medisch Centrum Utrecht, The Netherlands.
Phys Imaging Radiat Oncol. 2018 Oct 2;7:58-64. doi: 10.1016/j.phro.2018.09.002. eCollection 2018 Jul.
Synthetic computed tomography (sCT) images enable magnetic resonance (MR)-based dose calculations. This work investigated whether a commercially available sCT generation solution was suitable for accurate dose calculations and position verification on patients with rectal cancer.
For twenty rectal cancer patients computed tomography (CT) images were rigidly registered to sCT images. Clinical volumetric modulated arc therapy plans were recalculated on registered CT and sCT images. Dose deviations were determined through gamma and voxelwise analysis. The impact on position verification was investigated by identifying differences in translations and rotation between cone-beam CT (CBCT) to CT and CBCT to sCT registrations.
Across twenty patients, within a threshold of 90% of the prescription dose, a gamma analysis (2%, 2 mm) mean pass rate of 95.2 ± 4.0% (±1 ) and mean dose deviation of -0.3 ± 0.2% of prescription dose were obtained. The mean difference of translations and rotations over ten patients (76 CBCTs) was <1 mm and <0.5° in all directions. In the sole posterior-anterior direction a mean systematic shift of 0.7 ± 0.6 mm was found.
Accurate MR-based dose calculations using a commercial sCT generation method were clinically feasible for treatment of rectal cancer patients. The accuracy of position verification was clinically acceptable. However, before clinical implementation future investigations will be performed to determine the origin of the systematic shift.
合成计算机断层扫描（sCT）图像可实现基于磁共振（MR）的剂量计算。本研究探讨了一种商用sCT生成解决方案是否适用于直肠癌患者的精确剂量计算和位置验证。
对20例直肠癌患者的计算机断层扫描（CT）图像与sCT图像进行刚性配准。在配准后的CT和sCT图像上重新计算临床容积调强弧形放疗计划。通过伽马分析和体素分析确定剂量偏差。通过识别锥形束CT（CBCT）与CT以及CBCT与sCT配准之间的平移和旋转差异，研究其对位置验证的影响。
在20例患者中，在处方剂量的90%阈值内，伽马分析（2%，2毫米）的平均通过率为95.2±4.0%（±1 ），平均剂量偏差为处方剂量的-0.3±0.2%。在所有方向上，10例患者（76次CBCT）的平移和旋转平均差异<1毫米且<0.5°。仅在前后方向发现平均系统偏移为0.7±0.6毫米。
使用商用sCT生成方法进行基于MR的精确剂量计算在临床上对于直肠癌患者的治疗是可行的。位置验证的准确性在临床上是可接受的。然而，在临床实施之前，将进行进一步研究以确定系统偏移的来源。
