12/2/2023 0 Comments 4d simulator online![]() ![]() To our knowledge, this is the first report using 4D-MRI in an online radiation therapy workflow. The purpose of this report is to describe our implementation and initial clinical experience using 4D-MRI driven MRgOART for abdominal SBRT on the Elekta Unity MR-Linac. In addition, 4D-MRI eliminates systematic offsets between planned and delivered anatomies arising from breath hold or triggered image acquisitions and free-breathing treatment deliveries. For MRgOART, a natural method of providing this information is four-dimensional (4D) MRI. With the small margins and high doses employed in stereotactic body radiotherapy (SBRT), knowledge of target and organs at risk (OAR) motion trajectories during free-breathing is critical. The adaptive plan from either ATP or ATS can then be delivered under continuous real-time MR imaging of the target.Īt the time of this writing, only free-breathing treatment deliveries are clinically supported on the Unity system fully automated motion management capabilities (e.g., respiratory gating, breath-hold gating, trailing, tracking, or real-time plan adaptation) are not yet clinically available. Once a daily MR image of the patient is obtained, online adaptive plans can be generated using one of two workflows: i) Adapt-To-Position (ATP) in which the reference plan is reoptimized with an isocenter shift determined from co-registration of the daily and reference images, or ii) Adapt-To-Shape (ATS) in which a new plan is generated based on the anatomy of the day. Therefore, every treatment fraction requires an adaptive plan. Unlike conventional linacs, the couch on the Unity system is restricted to motion along the superior-inferior direction and is not allowed to move once the patient is positioned. In addition to providing high soft tissue contrast for anatomical definition and enabling intrafraction motion monitoring, the Unity system also permits acquisition of quantitative MR images for treatment response monitoring. One such system capable of performing these treatments is the Elekta Unity MR-Linac, which combines a Philips 1.5 T MRI with a flattening filter free (FFF) Elekta 7MV linear accelerator. MR-guided online adaptive radiotherapy (MRgOART) offers unique potential to safely escalate radiotherapy doses to mobile tumors in the abdomen.
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