MR-guided Gated Stereotactic Radiation Therapy Delivery for Lung, Adrenal, and Pancreatic Tumors : A Geometric Analysis

摘要: Purpose We implemented magnetic resonance–guided breath-hold stereotactic body radiation therapy in combination with visual feedback using the MRIdian system. Both accuracy of gated delivery and reproducibility tumor positions were studied. Methods Materials Tumor tracking is realized through repeated resonance imaging a single sagittal plane at 4 frames per second deformable image registration. An in-room monitor allowed visualization tracked gross volume (GTV) contour planning target (PTV) (GTV + 3 mm), which was gating boundary. For each delivery, predefined threshold-region interest percentage (ROI%) allows GTV area to be outside boundary before beam-hold triggered. Accuracy position during breath-holds analyzed for 15 patients (87 fractions) lung, adrenal, pancreas tumors. fraction, we (1) system-tracked centroid within PTV; (2) geometric coverage (3) treatment duty cycle efficiency; (4) effects threshold ROI% settings on efficiency coverage; (5) beam-off latency effect mean coverage. Results pancreatic tumors, grouped 5th 95th percentile distributions dorsoventral direction, relative PTV-center mass (COM), were, respectively, −3.3 mm 2.8 mm, −2.5 mm 3.7 mm, −4.4 mm 2.9 mm. Corresponding craniocaudal direction −2.6 mm 4.6 mm, −4.1 mm 4.4 mm, 4.5 mm, respectively. Mean areas encompassed beam-on all fractions 94.6%, 94.3%, 95.3% ranged from 67% 87% these Use higher threshold-ROI% resulted increased efficiency, cost small decrease The had marginal impact Conclusions Gated breath-hold, real-time guidance least 95%