Maziero Danilo, Straza Michael W, Ford John C, Bovi Joseph A, Diwanji Tejan, Stoyanova Radka, Paulson Eric S, Mellon Eric A
Department of Radiation Oncology, Sylvester Comprehensive Cancer Center, Miller School of Medicine, University of Miami, Miami, FL, United States.
Department of Radiation Oncology, Medical College of Wisconsin, Milwaukee, WI, United States.
Front Oncol. 2021 Mar 8;11:626100. doi: 10.3389/fonc.2021.626100. eCollection 2021.
MRI is the standard modality to assess anatomy and response to treatment in brain and spine tumors given its superb anatomic soft tissue contrast (e.g., T1 and T2) and numerous additional intrinsic contrast mechanisms that can be used to investigate physiology (e.g., diffusion, perfusion, spectroscopy). As such, hybrid MRI and radiotherapy (RT) devices hold unique promise for Magnetic Resonance guided Radiation Therapy (MRgRT). In the brain, MRgRT provides daily visualizations of evolving tumors that are not seen with cone beam CT guidance and cannot be fully characterized with occasional standalone MRI scans. Significant evolving anatomic changes during radiotherapy can be observed in patients with glioblastoma during the 6-week fractionated MRIgRT course. In this review, a case of rapidly changing symptomatic tumor is demonstrated for possible therapy adaptation. For stereotactic body RT of the spine, MRgRT acquires clear isotropic images of tumor in relation to spinal cord, cerebral spinal fluid, and nearby moving organs at risk such as bowel. This visualization allows for setup reassurance and the possibility of adaptive radiotherapy based on anatomy in difficult cases. A review of the literature for MR relaxometry, diffusion, perfusion, and spectroscopy during RT is also presented. These techniques are known to correlate with physiologic changes in the tumor such as cellularity, necrosis, and metabolism, and serve as early biomarkers of chemotherapy and RT response correlating with patient survival. While physiologic tumor investigations during RT have been limited by the feasibility and cost of obtaining frequent standalone MRIs, MRIgRT systems have enabled daily and widespread physiologic measurements. We demonstrate an example case of a poorly responding tumor on the 0.35 T MRIgRT system with relaxometry and diffusion measured several times per week. Future studies must elucidate which changes in MR-based physiologic metrics and at which timepoints best predict patient outcomes. This will lead to early treatment intensification for tumors identified to have the worst physiologic responses during RT in efforts to improve glioblastoma survival.
鉴于其出色的解剖软组织对比度（如T1和T2）以及可用于研究生理学的众多额外固有对比机制（如扩散、灌注、波谱分析），MRI是评估脑和脊柱肿瘤的解剖结构及治疗反应的标准检查方法。因此，MRI与放射治疗（RT）的混合设备对磁共振引导放射治疗（MRgRT）具有独特的前景。在脑部，MRgRT可每日可视化不断演变的肿瘤，这是锥形束CT引导下无法看到的，且偶尔进行的独立MRI扫描也无法完全表征。在为期6周的分次MRI引导放射治疗过程中，胶质母细胞瘤患者在放射治疗期间可观察到显著的解剖结构演变。在本综述中，展示了一例症状性肿瘤快速变化的病例，以探讨可能的治疗适应性。对于脊柱的立体定向体部放射治疗，MRgRT可获取肿瘤相对于脊髓、脑脊液以及附近有风险的活动器官（如肠道）的清晰各向同性图像。这种可视化有助于确保摆位的准确性，并在困难病例中基于解剖结构进行自适应放射治疗。本文还对放射治疗期间的磁共振弛豫测量、扩散、灌注和波谱分析的文献进行了综述。这些技术已知与肿瘤的生理变化相关，如细胞密度、坏死和代谢，并作为化疗和放射治疗反应的早期生物标志物，与患者生存率相关。虽然放射治疗期间对肿瘤生理状况的研究受到频繁进行独立MRI检查的可行性和成本的限制，但MRI引导放射治疗系统已实现了每日且广泛的生理测量。我们展示了一个在0.35 T MRI引导放射治疗系统上对治疗反应不佳的肿瘤的示例病例，每周进行多次弛豫测量和扩散测量。未来的研究必须阐明基于磁共振的生理指标的哪些变化以及在哪些时间点最能预测患者的预后。这将导致对在放射治疗期间被确定为生理反应最差的肿瘤进行早期强化治疗，以努力提高胶质母细胞瘤患者的生存率。
