Department of Oncology and Nuclear Medicine, Sestre milosrdnice University Hospital Center, Vinogradska 29, 10000 Zagreb, Croatia.
Department of Medical Physics, Sestre milosrdnice University Hospital Center, Vinogradska 29, 10000 Zagreb, Croatia.
Acta Clin Croat. 2022 Oct;61(Suppl 3):65-70. doi: 10.20471/acc.2022.61.s3.9.
Radiotherapy is one of the key treatment modalities for primary prostate cancer. During the last decade, significant advances were made in radiotherapy technology leading to increasing both physical and biological precision. Being a loco-regional treatment approach, radiotherapy requires accurate target dose deposition while sparing surrounding healthy tissue. Conventional radiotherapy is based on computerized tomography (CT) images both for radiotherapy planning and image-guidance, however, shortcomings of CT as soft tissue imaging tool are well known. Nowadays, our ability to further escalate radiotherapy dose using hypofractionation is limited by uncertainties in CT-based image guidance and verification. Magnetic resonance imaging (MRI) is a well established imaging method for pelvic organs. In prostate cancer specifically, MRI accurately depicts prostate zonal anatomy, rectum, bladder, and pelvic floor structures with previously unseen precision owing to its sharp soft tissue contrast. The advantages of including MRI in the clinical workflow of prostate cancer radiotherapy are multifold. MRI allows for true adaptive radiotherapy to unfold based on daily MRI images taken before, during and after each radiotherapy fraction. It enables accurate dose escalation to the prostate and intraprostatic tumor lesions. Technically, MRI high-strength magnetic field and linear accelerator high energy electromagnetic beams are hardly compatible, and important efforts were made to overcome these technical challenges and integrate MRI and linear accelerator into one single treatment device, called MRI-linac. Different systems are produced by two leading vendors in the field and currently, there are around 100 MRI-linacs worldwide in clinical operations. In this narrative review paper, we discuss historical perspective of image guidance in radiotherapy, basic elements of MRI, current clinical developments in MRI-guided prostate cancer radiotherapy, and challenges associated with the use of MRI-linac in clinical practice.
放射治疗是治疗原发性前列腺癌的主要方法之一。在过去的十年中，放射治疗技术取得了重大进展，提高了物理和生物精度。作为一种局部治疗方法，放射治疗需要在准确沉积靶剂量的同时保护周围的健康组织。常规放射治疗基于计算机断层扫描（CT）图像进行放射治疗计划和图像引导，但 CT 作为软组织成像工具的缺点是众所周知的。如今，我们使用适形调强放射治疗进一步提高放射剂量的能力受到基于 CT 的图像引导和验证的不确定性的限制。磁共振成像（MRI）是一种成熟的盆腔器官成像方法。在前列腺癌中，MRI 能够以前所未有的精度准确描绘前列腺分区解剖结构、直肠、膀胱和骨盆底结构，这要归功于其锐利的软组织对比度。将 MRI 纳入前列腺癌放射治疗的临床工作流程具有多种优势。MRI 允许根据每次放射治疗前后拍摄的每日 MRI 图像进行真正的自适应放射治疗。它能够实现对前列腺和前列腺内肿瘤病变的准确剂量递增。从技术上讲，MRI 的强磁场和直线加速器的高能电磁场很难兼容，因此，人们做出了重要努力来克服这些技术挑战，并将 MRI 和直线加速器集成到一个称为 MRI 直线加速器的单一治疗设备中。该领域的两个领先供应商生产了不同的系统，目前，全球约有 100 台 MRI 直线加速器在临床运行。在这篇叙述性综述文章中，我们讨论了放射治疗图像引导的历史背景、MRI 的基本要素、目前 MRI 引导前列腺癌放射治疗的临床进展，以及 MRI 直线加速器在临床实践中使用所面临的挑战。
