Nowee M E, van Pelt V W J, Walraven I, Simões R, Liskamp C P, Lambregts D M J, Heijmink S, Schaake E, van der Heide U A, Janssen T M
Department of Radiation Oncology, The Netherlands Cancer Institute, Amsterdam, The Netherlands.
Department of Radiology, The Netherlands Cancer Institute, Amsterdam, The Netherlands.
Phys Imaging Radiat Oncol. 2021 Jul 24;19:85-89. doi: 10.1016/j.phro.2021.07.002. eCollection 2021 Jul.
Magnetic resonance (MR) guided radiotherapy utilizes MR images for (online) plan adaptation and image guidance. The aim of this study was to investigate the impact of variation in MR acquisition time and scan resolution on image quality, interobserver variation in contouring and interobserver variation in registration.
Nine patients with prostate cancer were included. Four T2-weighted 3D turbo spin echo (T2w 3D TSE) sequences were acquired with different acquisition times and resolutions. Two radiologists assessed image quality, conspicuity of the capsule, peripheral zone and central gland architecture and motion artefacts on a 5 point scale. Images were delineated by two radiation oncologists and interobserver variation was assessed by the 95% Hausdorff distance. Seven observers registered the MR images on the planning CT. Registrations were compared on systematic offset and interobserver variation.
Acquisition times ranged between 1.3 and 6.3 min. Overall image quality and capsule definition were significantly worse for the MR sequence with an acquisition time of 1.3 min compared to the other sequences. Median 95% Hausdorff distance showed no significant differences in interobserver variation of contouring. Systematic offset and interobserver variation in registration were small (<1 mm) and of no clinical significance.
Our results can be used to effectively shorten overall fraction time for online adaptive MR guided radiotherapy by optimising the imaging sequence used for registration. From the sequences studied, a sequence of 3.1 min with anisotropic voxels of 1.2 × 1.2 × 2.4 mm provided the shortest acquisition time without compromising image quality.
磁共振（MR）引导的放射治疗利用MR图像进行（在线）计划调整和图像引导。本研究的目的是调查MR采集时间和扫描分辨率的变化对图像质量、轮廓勾画的观察者间差异以及配准的观察者间差异的影响。
纳入9例前列腺癌患者。采用不同的采集时间和分辨率获取4个T2加权三维快速自旋回波（T2w 3D TSE）序列。两名放射科医生以5分制评估图像质量、包膜、外周带和中央腺体结构的清晰度以及运动伪影。由两名放射肿瘤学家勾画图像，并通过95%豪斯多夫距离评估观察者间差异。7名观察者将MR图像与计划CT进行配准。比较配准的系统偏移和观察者间差异。
采集时间在1.3至6.3分钟之间。与其他序列相比，采集时间为1.3分钟的MR序列的整体图像质量和包膜清晰度明显较差。中位数95%豪斯多夫距离显示轮廓勾画的观察者间差异无显著差异。配准的系统偏移和观察者间差异较小（<1毫米），无临床意义。
我们的结果可用于通过优化用于配准的成像序列，有效缩短在线自适应MR引导放射治疗的总分次时间。在所研究的序列中，采集时间为3.1分钟、各向异性体素为1.2×1.2×2.4毫米的序列在不影响图像质量的情况下提供了最短的采集时间。
