Program Information
Automatic Prostate Intrafraction Motion Management
W Liu*, R Nath , Yale Univ. School of Medicine, New Haven, CT
Presentations
TH-AB-303-11 (Thursday, July 16, 2015) 7:30 AM - 9:30 AM Room: 303
Purpose: Intrafraction motion management is important for prostate radiotherapy when tight margin is used especially for hypo-fractional treatment. We evaluate the benefits of imaging strategies in the situation of manual and automatic motion correction.
Methods: Prostate position information was acquired continuously using electromagnetic transponder at two institutions from 17 and 30 patients (536 and 883 trajectories), respectively. We simulated 7-field IMRT delivery with periodic imaging at various frequencies and with continuous adaptive imaging. With manual correction, we assumed correction is applied when the displacement is greater than a predefined threshold and there is a 30 sec delay after imaging to determine and apply the couch shift. With automatic correction, we assumed 1 sec delay. For adaptive imaging, real-time “dose-free” cine-MV imaging during treatment is used in conjunction with online-updated motion pattern to estimate 3D displacement. Automatic MV-kV imaging is only used to confirm over-threshold motion and calculate couch shift, therefore very low additional patient dose from kV imaging.
Results: There was no significant bias from either cohort since the results from the two institutions are similar. Compared to the initial setup position, without intervention, on average, the prostates moved out of a 3-mm margin for 9.2% of the beam-on time. With automatic correction, 3-min imaging and correction frequency reduces the mean percentage to 4.7%. With manual correction, however, the percentage is only reduced to 8.4%, minor improvement compared to no imaging. The maximal patient-specific over-3mm time is 24.3%. The adaptive imaging strategy reduces the mean percentage to 0.9% and the maximum to 1.5%. On average, only 2.5 kV images are needed per fraction, similar to 3-min periodic imaging. The targeting performance is achieved by only 1.0 couch shift per fraction.
Conclusion: Adaptive continuous monitoring with automatic motion compensation is more beneficial than periodic imaging surveillance at similar imaging dose.
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