World's First Application of MR-Guidance for Radiotherapy.

Radiotherapy localization is the process by which patient treatments are aligned on a daily basis. Localization has hiistorically been accomplished using 2-dimensional x-ray images, or cone-beam CT- imaging which permits excellent visualization of bony anatomy, but suboptimal soft-tissue imaging. The Department of Radiation Oncology at Washington University recently implemented the world's first MR-Image Guided Radiation Therapy program (MR-IGRT), which utilizes a O.35T MR scanner integrated with three 6"Co heads for treatment delivery. A high-resolution volumetric MR image is acquired for each patient at the time of daily treatment setup, which allows localization based on soft-tissue anatomy, and modification to the treatment plan when required while the patient is on the treatment table. Herein, we review principles of radiotherapy localization, describe implementation of the world's first MR-IGRT program, and present future directions where MR-IGRT may be applied for patient treatments.