Initial Feasibility and Clinical Implementation of Daily MR-Guided Adaptive Head and Neck Cancer Radiation Therapy on a 1.5T MR-Linac System: Prospective R-IDEAL 2a/2b Systematic Clinical Evaluation of Technical Innovation

Purpose This prospective study is, to our knowledge, the first report of daily adaptive radiation therapy (ART) for head and neck cancer (HNC) using a 1.5T magnetic resonance imaging-linear accelerator (MR-linac) with particular focus on safety feasibility dosimetric results an online rigid registration-based adapt position (ATP) workflow. Methods Materials Ten patients HNC received ART 1.5T/7MV MR-linac, 6 ATP only 4 1 offline adapt-to-shape replan. Setup variability custom immobilization masks was assessed by calculating mean systematic error (M), standard deviation (?), random (?) isocenter shifts. Quality assurance performed cylindrical diode array 3%/3 mm ? criteria. Adaptive treatment plans were summed each patient compare delivered dose planned from reference plan. The impact between fractions summation plan doses tracking number optimization constraint violations at individual fraction. Results errors (mm) x, y, z shifts, respectively, M=–0.3, 0.7, 0.1; ? = 3.3, 2.6, 1.4; ? 1.7, 2.9, 1.0. median (range) pass rate 99.9% (90.9%-100%). differences –0.61% 1.78% clinical target volume –11.74% 8.11% organs risk (OARs), although increase greater than 2% in OAR occurred 3 cases, single OAR. All cases had least 2 or more violations. However, nearly all instances, constraints still met despite multiple single-fraction Conclusions Daily MR-linac workflow is safe clinically feasible consistent doses.