First MR images obtained during megavoltage photon irradiation from a prototype integrated linac-MR system
First MR images obtained during megavoltage photon irradiation from a prototype integrated linac-MR system
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DOI：
10.1118/1.3125662
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发表时间：
2009-06-01
期刊：
影响因子：
3.8
通讯作者：
Tymofichuk, D.
中科院分区：
文献类型：
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作者：
Fallone, B. G.;Murray, B.;Tymofichuk, D.
作者报告了他们的原型MR系统与放射治疗源集成产生的第一个磁共振（MR）图像。原型包括一个6 MV直线加速器，安装在双平面0.2 T永久磁流变系统的开口端，该系统具有27.9厘米的极对极开口和平坦梯度（40 mT/m），在TMX NRC控制台下运行。磁体等心到直线靶的距离为80 cm。作者的设计解决了两个器件之间的相互干扰，使磁磁共振磁场不会干扰直线波导中电子的轨迹，并且来自每个系统的射频信号不会干扰另一个系统的工作。进行了磁屏蔽和射频屏蔽计算，并通过适当的测量进行了验证。原型机目前在一个固定的龙门架上；然而，在不久的将来，直线加速器和磁通磁体将同步旋转，直线加速器总是通过双面磁体的开口瞄准。在直线辐射期间，磁共振成像被发现是完全可操作的，并通过成像传统的梯度回波序列来证明幻体。除了信噪比的微小变化外，辐照期间产生的MR图像在视觉上和数量上与关闭直线发生器时的图像非常相似。该原型系统提供了概念证明，该设计已经充分减少了相互干扰，从而允许实时磁共振引导放射治疗的发展。低场强系统（0.2-0.5 T）在临床上被用作诊断工具。然而，直线-磁共振系统的任务是为放射治疗光束提供磁共振引导。因此，0.2 T的场强将为这一目的提供足够的图像质量，并且加上快速成像技术，有可能提供目前在图像引导放射治疗系统中无法提供的4D软组织可视化。作者最初的设计包含一个永磁体；然而，其他类型的磁铁和磁场强度也可以被纳入。在直线辐射过程中，从直线-磁共振原型中获得可用的磁共振图像。作者的原型设计可以作为开发实时MR引导的功能起点，提供软组织对比，可以与实时适应性放疗的肿瘤跟踪相结合。
The authors report the first magnetic resonance (MR) images produced by their prototype MR system integrated with a radiation therapy source. The prototype consists of a 6 MV linac mounted onto the open end of a biplanar 0.2 T permanent MR system which has 27.9 cm pole-to-pole opening with flat gradients (40 mT/m) running under a TMX NRC console. The distance from the magnet isocenter to the linac target is 80 cm. The authors' design has resolved the mutual interferences between the two devices such that the MR magnetic field does not interfere with the trajectory of the electron in the linac waveguide, and the radiofrequency (RF) signals from each system do not interfere with the operation of the other system. Magnetic and RF shielding calculations were performed and confirmed with appropriate measurements. The prototype is currently on a fixed gantry; however, in the very near future, the linac and MR magnet will rotate in unison such that the linac is always aimed through the opening in the biplanar magnet. MR imaging was found to be fully operational during linac irradiation and proven by imaging a phantom with conventional gradient echo sequences. Except for small changes in SNR, MR images produced during irradiation were visually and quantitatively very similar to those taken with the linac turned off. This prototype system provides proof of concept that the design has decreased the mutual interferences sufficiently to allow the development of real-time MR-guided radiotherapy. Low field-strength systems (0.2-0.5 T) have been used clinically as diagnostic tools. The task of the linac-MR system is, however, to provide MR guidance to the radiotherapy beam. Therefore, the 0.2 T field strength would provide adequate image quality for this purpose and, with the addition of fast imaging techniques, has the potential to provide 4D soft-tissue visualization not presently available in image-guided radiotherapy systems. The authors' initial design incorporates a permanent magnet; however, other types of magnets and field strengths could also be incorporated. Usable MR images were obtained during linac irradiation from the linac-MR prototype. The authors' prototype design can be used as the functional starting point in developing real-time MR guidance offering soft-tissue contrast that can be coupled with tumor tracking for real-time adaptive radiotherapy.