(Saturday, 4/4/2020) [Mountain Time (GMT-6)]
Purpose: Adaptive radiation therapy (ART) planning deals with organ motion and anatomical changes during a course of radiotherapy. MRI guided radiotherapy gives added boost to online ART planning with no unnecessary radiation dose to the patient. The MRIdian system (ViewRay, Inc., Cleveland, OH) is one of such online imaging systems on which one can re-optimize a treatment plan. This enhancement also increases some risks; hence it is critical to examine each step involved in the entire adaptive workflow.
Methods: We studied five clinical sites: lung, liver, pancreas, stomach, rectum and abdominal sarcomas. All patients were planned on ViewRay’s treatment planning system. The indication for adaptation was assessed considering critical organ displacement and organ filling causing noncompliance with the original treatment plan. Physicist re-optimized the original treatment plan for treatment day anatomy changes after verifying the electron density. A secondary check is performed on re-optimized plans before treatment delivery. Validation of predicted dose and delivered dose were done for post adapted plan delivery. Patient safety and tolerance, staffing needs, over all treatment time were studied.
Results: Patients positioned with arms down helps to define a 4 cm ring around PTV for contour editing. It speeds up contouring and re-optimization. Superior sparing of critical structures overlapping the target is achieved. It also improves target coverage by ~10 to 15% on days when critical structures are displaced away from PTV. Maximum dose to duodenum, bowel, bronchus could be lowered to meet treatment planning objective (V45 < 0.05 cc). It is important to consider patient safety and tolerance, staffing needs and overall treatment time.
Conclusion: Several challenges need addressing in order to achieve optimum benefits from MRI guided ART. Some of these are identified. This approach is considerably superior to existing solutions and requires adequate staffing and training for deriving maximum benefit.
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