The Christie NHS Foundation Trust, Department of Radiotherapy, Manchester, United Kingdom.
The Christie NHS Foundation Trust, Department of Clinical Oncology, Manchester, United Kingdom.
J Med Imaging Radiat Sci. 2024 Dec;55(4):101716. doi: 10.1016/j.jmir.2024.101716. Epub 2024 Jul 20.
This work reports on an unusual finding observed during image quality assessment in the preparation for the clinical implementation of breast magnetic resonance image-guided radiotherapy (MRIgRT) on a 1.5 Tesla (T) magnetic resonance linear accelerator (MR-Linac) (Elekta AB, Stockholm, Sweden).
A patient with T2 N0 M0 right breast invasive ductal carcinoma, receiving adjuvant radiotherapy, underwent two imaging sessions on the MR-Linac. The imaging protocol included T1- and T2-weighted (W) turbo spin echo (TSE) sequences, a T1W mDixon, and a T2W TSE navigated sequence acquired on end-expiration. All images were reconstructed in the axial plane. Images were assessed for image quality and appropriateness for use within the treatment pathway using visual grading analysis (VGA). An artefact in the right breast was noted independently by all observers. The patient's skin and medical notes were reviewed for possible explanation. The findings were discussed with the patient's responsible clinician, and subsequent referral to the local multi-disciplinary team (MDT) for radiologist review was made. On further investigation, the patient's images demonstrated a signal void in the subareolar region of the right breast coinciding with the surgical site. This was distal from the tumour bed and deemed unlikely to be related to a Magseed marker or intraoperative clips. The patient reported no history of nipple tattoo or piercing. There was nothing on clothing that this could be attributed to.
Following MDT review, where all potential sources of signal void were considered, it was concluded that the cause was Magtrace, a superparamagnetic iron oxide tracer, recommended for sentinel lymph node localisation in patients with breast cancer in the United Kingdom. The artefact was characteristic of a magnetic susceptibility artefact. These can arise from local magnetic field inhomogeneities caused by the presence of the metal compounds in MagTrace. For breast MRIgRT on the MR-Linac, treatment verification and the possibility of real-time replanning is a critical aspect. The magnetic susceptibility artefact significantly inhibited plan adaption and confidence in the online image registration process making the patient ineligible for treatment on the MR-Linac.
As part of ongoing work-up for breast MRIgRT, the screening of patients for Magtrace is now included. Optimisation of MR imaging sequences for radiotherapy planning and image review to minimise distortion are being developed.
本研究报告了在准备将乳腺磁共振图像引导放疗（MRIgRT）应用于 1.5T 磁共振直线加速器（MR-Linac）（瑞典 Elekta AB）的临床实施过程中，在图像质量评估中观察到的一种异常发现。
一位 T2N0M0 右乳腺浸润性导管癌患者，接受辅助放疗，在 MR-Linac 上进行了两次影像学检查。成像方案包括 T1 和 T2 加权（W）涡轮自旋回波（TSE）序列、T1W mDixon 和 T2W TSE 导航序列，均在呼气末采集。所有图像均在轴位重建。使用视觉分级分析（VGA）评估图像质量和是否适合治疗途径。所有观察者均独立观察到右乳房存在伪影。审查了患者的皮肤和病历以寻找可能的解释。将发现与患者的主治临床医生进行了讨论，并随后转介给当地的多学科团队（MDT）进行放射科医生审查。进一步调查显示，患者的图像显示右乳腺乳晕下区域存在信号缺失，与手术部位一致。该区域远离肿瘤床，不太可能与 Magseed 标记或术中夹有关。患者报告没有乳头纹身或穿孔的病史。衣服上没有任何东西可以归因于此。
在 MDT 审查后，考虑了所有潜在的信号缺失源，认为原因是 Magtrace，一种超顺磁性氧化铁示踪剂，在英国推荐用于乳腺癌患者的前哨淋巴结定位。该伪影是磁敏感性伪影的特征。这些伪影可能是由于 MagTrace 中金属化合物的存在导致局部磁场不均匀引起的。对于 MR-Linac 上的乳腺 MRIgRT，治疗验证和实时重新规划的可能性是一个关键方面。磁敏感性伪影严重抑制了计划适应和在线图像配准过程的信心，使患者不符合 MR-Linac 的治疗条件。
作为乳腺 MRIgRT 正在进行的工作的一部分，现在包括对 Magtrace 进行患者筛查。正在开发用于放射治疗计划和图像审查的优化磁共振成像序列，以最大程度地减少失真。
