Edmund Jens M, Andreasen Daniel, Van Leemput Koen
Radiotherapy Research Unit, Department of Oncology, Gentofte and Herlev Hospital, University of Copenhagen, 2730 Herlev, Denmark.
Niels Bohr Institute, University of Copenhagen, 2100 Copenhagen, Denmark.
Phys Imaging Radiat Oncol. 2021 May 13;18:55-60. doi: 10.1016/j.phro.2021.05.001. eCollection 2021 Apr.
Radiotherapy (RT) based on magentic resonance imaging (MRI) only is currently used clinically in the pelvis. A synthetic computed tomography (sCT) is needed for dose planning. Here, we investigate the accuracy of cone beam CT (CBCT) based MRI-only image guided RT (IGRT) and sCT image quality.
CT, MRI and CBCT scans of ten prostate cancer patients were included. The MRI was converted to a sCT using a multi-atlas approach. The sCT, CT and MR images were auto-matched with the CBCT on the bony anatomy. Paired sCT-CT and sCT-CBCT data were created. CT numbers were converted to relative electron (RED) and mass densities (DES) using a standard calibration curve for the CT and sCT. For the CBCT RED/DES conversion, a phantom and paired CT-CBCT population based calibration curve was used. For the latter, the CBCT numbers were averaged in 100 HU bins and the known RED/DES of the CT were assigned. The paired sCT-CT and sCT-CBCT data were averaged in bins of 10 HU or 0.01 RED/DES. The median absolute error (MeAE) between the sCT-CT and sCT-CBCT bins was calculated. Wilcoxon rank-sum tests were carried out for the IGRT and MeAE study.
The mean sCT or MR IGRT difference from CT was ≤ 2 mm but significant differences were observed. A CBCT HU or phantom-based RED/DES MeAE did not estimate the sCT quality similar to a CT based MeAE but the CBCT population-based RED/DES MeAE did.
MRI-only CBCT-based IGRT seems feasible but caution is advised. A MeAE around 0.1 DES could call for sCT quality inspection.
目前临床上仅基于磁共振成像（MRI）的放射治疗（RT）用于盆腔部位。剂量规划需要合成计算机断层扫描（sCT）。在此，我们研究基于锥形束CT（CBCT）的仅MRI图像引导放射治疗（IGRT）的准确性以及sCT图像质量。
纳入10例前列腺癌患者的CT、MRI和CBCT扫描数据。使用多图谱方法将MRI转换为sCT。sCT、CT和MR图像在骨骼解剖结构上与CBCT自动匹配。创建配对的sCT-CT和sCT-CBCT数据。使用CT和sCT的标准校准曲线将CT值转换为相对电子密度（RED）和质量密度（DES）。对于CBCT的RED/DES转换，使用体模和基于配对CT-CBCT人群的校准曲线。对于后者，将CBCT值在100 HU区间内平均，并指定已知的CT的RED/DES。配对的sCT-CT和sCT-CBCT数据在10 HU或0.01 RED/DES的区间内平均。计算sCT-CT和sCT-CBCT区间之间的中位数绝对误差（MeAE）。对IGRT和MeAE研究进行Wilcoxon秩和检验。
sCT或MR与CT的平均IGRT差异≤2 mm，但观察到显著差异。基于CBCT HU或体模的RED/DES MeAE与基于CT的MeAE相比，不能类似地估计sCT质量，但基于CBCT人群的RED/DES MeAE可以。
仅基于MRI的CBCT的IGRT似乎可行，但建议谨慎使用。MeAE约为0.1 DES时可能需要进行sCT质量检查。
