Khoo V S, Dearnaley D P, Finnigan D J, Padhani A, Tanner S F, Leach M O
Department of Radiotherapy and Oncology, Royal Marsden NHS Trust, Sutton, Surrey, UK.
Radiother Oncol. 1997 Jan;42(1):1-15. doi: 10.1016/s0167-8140(96)01866-x.
The emerging utilisation of conformal radiotherapy (RT) planning requires sophisticated imaging modalities. Magnetic resonance imaging (MRI) has introduced several added imaging benefits that may confer an advantage over the use of computed tomography (CT) in RT planning such as improved soft tissue definition, unrestricted multiplannar and volumetric imaging as well as physiological and biochemical information with magnetic resonance (MR) angiography and spectroscopy. However, MRI has not yet seriously challenged CT for RT planning in most sites. The reasons for this include: (1) the poor imaging of bone and the lack of electron density information from MRI required for dosimetry calculations; (2) the presence of intrinsic system-related and object-induced MR image distortions; (3) the paucity of widely available computer software to accurately and reliably integrate and manipulate MR images within existing RT planning systems. In this review, the basic principals of MRI with its present potential and limitations for RT planning as well as possible solutions will be examined. Methods of MRI data acquisition and processing including image segmentation and registration to allow its application in RT planning will be discussed. Despite the difficulties listed, MRI has complemented CT-based RT planning and in some regions of the body especially the brain, it has been used alone with some success. Recent work with doped gel compounds allow the MRI mapping of dose distributions thus potentially providing a quality assurance tool and in a manner analogous to CT, the production of dose-response information in the form of dose volume histograms. However, despite the promise of MRI, much development research remains before its full potential and cost-effectiveness can be assessed.
适形放射治疗（RT）计划的新兴应用需要复杂的成像方式。磁共振成像（MRI）带来了一些额外的成像优势，在RT计划中可能比使用计算机断层扫描（CT）更具优势，例如改善软组织清晰度、不受限制的多平面和容积成像，以及通过磁共振（MR）血管造影和光谱提供的生理和生化信息。然而，在大多数部位的RT计划中，MRI尚未对CT构成严重挑战。其原因包括：（1）骨骼成像不佳，且MRI缺乏剂量计算所需的电子密度信息；（2）存在与系统相关的固有以及由物体引起的MR图像畸变；（3）缺乏广泛可用的计算机软件来在现有的RT计划系统中准确可靠地整合和处理MR图像。在本综述中，将探讨MRI的基本原理及其在RT计划中的当前潜力、局限性以及可能的解决方案。将讨论MRI数据采集和处理的方法，包括图像分割和配准，以使其能够应用于RT计划。尽管存在上述困难，MRI已对基于CT的RT计划起到补充作用，在身体的某些部位尤其是脑部，它已单独使用并取得了一定成功。最近对掺杂凝胶化合物的研究使得能够通过MRI绘制剂量分布，从而有可能提供一种质量保证工具，并且类似于CT，以剂量体积直方图的形式生成剂量反应信息。然而，尽管MRI前景广阔，但在能够评估其全部潜力和成本效益之前，仍有许多研发工作要做。
