放射治疗 (RT) 是肿瘤治疗的核心支柱，一半的癌症患者接受这种治疗作为治愈或姑息治疗。最近将 MRI 集成到 RT 工作流程中导致了 MRI 引导 RT (MRIgRT) 的出现。使用 MRI 而不是 CT 在引导盆腔肿瘤放疗方面具有明显的优势，包括卓越的软组织对比度、改进的器官运动可视化以及对肿瘤表型特征进行成像的潜力，以确定最具侵袭性或最难治疗的区域，这些区域可以作为目标具有更集中的更高辐射剂量。放射科医生应熟悉 MRI 在规划盆腔放疗中的潜在用途；使用的各种 RT 技术，例如近距离放射治疗和外照射 RT；以及 MRIgRT 对治疗模式的影响。讨论了 MRIgRT 在前列腺癌、宫颈癌和膀胱癌治疗中的当前临床经验和证据基础，并举例说明了治疗病例。此外，还强调了 MRIgRT 的优势，例如 RT 的实时在线适应（治疗期间）和对器官运动的分次间和/或分次内适应，以及 MRIgRT 如何减少毒性作用和改善肿瘤学结果。 MRIgRT 对于治疗移动盆腔结构特别有益，并且可以通过使用先进的 MRI 引导直线加速器系统来实现肿瘤的实时自适应 RT，以保护处于危险中的器官。还概述了利用功能性 MRI 序列和放射基因组方法开发生物驱动的适应性 RT 的未来机会。 ©RSNA，2023 本文的测验问题可在补充材料中找到。

Radiation therapy (RT) is a core pillar of oncologic treatment, and half of all patients with cancer receive this therapy as a curative or palliative treatment. The recent integration of MRI into the RT workflow has led to the advent of MRI-guided RT (MRIgRT). Using MRI rather than CT has clear advantages for guiding RT to pelvic tumors, including superior soft-tissue contrast, improved organ motion visualization, and the potential to image tumor phenotypic characteristics to identify the most aggressive or treatment-resistant areas, which can be targeted with a more focal higher radiation dose. Radiologists should be familiar with the potential uses of MRI in planning pelvic RT; the various RT techniques used, such as brachytherapy and external beam RT; and the impact of MRIgRT on treatment paradigms. Current clinical experience with and the evidence base for MRIgRT in the settings of prostate, cervical, and bladder cancer are discussed, and examples of treated cases are illustrated. In addition, the benefits of MRIgRT, such as real-time online adaptation of RT (during treatment) and interfraction and/or intrafraction adaptation to organ motion, as well as how MRIgRT can decrease toxic effects and improve oncologic outcomes, are highlighted. MRIgRT is particularly beneficial for treating mobile pelvic structures, and real-time adaptive RT for tumors can be achieved by using advanced MRI-guided linear accelerator systems to spare organs at risk. Future opportunities for development of biologically driven adapted RT with use of functional MRI sequences and radiogenomic approaches also are outlined. ©RSNA, 2023 Quiz questions for this article are available in the supplemental material.