By Daniel Cagney, MD
December 12, 2017
High-precision radiation treatment techniques can deliver high doses of radiation to tumors with submillimeter accuracy while sparing normal healthy tissues. The advancements of radiation therapy techniques have relied on high resolution radiological imaging to ensure accurate delivery of treatment. Currently, most radiation treatment planning is performed via CT-based imaging, and image-guided radiation is delivered using CT or X-ray imaging with alignment to bone/implanted markers as surrogates of tumor location. For several cancers, CT imaging alone is inadequate to accurately and precisely delineate the tumor. Frequently it is necessary to acquire additional higher resolution or metabolic imaging, such as diagnostic MRI and/or PET scans. These images are then combined to the CT images in a post-hoc manner to aid in tumor delineation. However, these registrations are often limited by variation in patient positioning and/or changes in tumor size/position over time.
Magnetic resonance imaging (MRI) provides several benefits over CT-based imaging in radiation oncology including higher soft tissue resolution, functional imaging, and continuous imaging without exposing patients to ionizing radiation.1,2 For radiation therapy of soft tissue tumors (e.g., breast, GI, GU, Gyn, head and neck, sarcoma), the higher resolution MRI can aid physicians to more accurately target tumors, thus ensuring more precise radiation therapy that can spare surrounding normal tissues, reduce toxicities, and improve outcomes for our patients. For example, the EMBRACE study3 has shown for cervical cancers treated with brachytherapy that MRI can improve tumor coverage and sparing of normal tissues from unnecessary radiation.
With MRI technology increasingly utilized for radiation therapy planning, the integration of MRI technology into linear accelerators (radiation treatment machines) is a natural evolution in radiation therapy delivery. Novel MR-guided linear accelerator devices will likely emerge as a new standard of care within the next decade due to improvements in soft tissue targeting and reduction in ionizing radiation exposure.4,5
Thus, MRI-based radiation therapy represents a significant technological advancement that will have notable impact in improving the delivery of high-resolution, highly accurate radiation treatments for a variety of cancer types.
- Kishan AU, Lee P. MRI-guided radiotherapy: opening our eyes to the future. Integr Cancer Sci Therap. 2016;3.
- Pollard JM, Wen Z, Sadagopan R, Wang J, Ibbott GS. The future of image-guided radiotherapy will be MR guided. Br J Radiol. 2017;90(1073):20160667.
- Pötter R, Georg P, Dimopoulos JC, Grimm M, Berger D, Nesvacil N, et al. Clinical outcome of protocol based image (MRI) guided adaptive brachytherapy combined with 3D conformal radiotherapy with or without chemotherapy in patients with locally advanced cervical cancer. Radiother Oncol. 2011;100(1):116-23.
- Mutic S, Dempsey JF, editors. The ViewRay system: Magnetic resonance–guided and controlled radiotherapy. Seminars in radiation oncology; Semin Radiat Oncol. 2014: Elsevier.
- Lagendijk JJ, Raaymakers BW, Raaijmakers AJ, Overweg J, Brown KJ, Kerkhof EM, et al. MRI/linac integration. Radiother Oncol. 2008;86(1):25-9. Elsevier.
Dr. Daniel Cagney is a clinical fellow in Radiation Oncology at Dana-Farber/Brigham and Womens’ Cancer Institute. His clinical interests include stereotactic radiation and integration of new technologies into radiation oncology practice.