Transformation of a 6DoF Robotic Couch Position to Account for Intrafraction Variation for a Proton Therapy System
Presentations
PO-GePV-M-108 (Sunday, 7/10/2022) [Eastern Time (GMT-4)]
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Purpose: To correct 6DOF robotic treatment couch positions recorded in the R&V system to reconcile the observed significant difference of couch vertical positions during the course of treatments.
Methods: The Verity imaging registration system of the Mevion Hyperscan proton system was used to match a pair of PA/Lat kV x-ray patient set-up images to plan DRRs. The required couch 6D shifts were applied to move the couch to the correct treatment position. The coordinate system for the 6DoF robotic couch varies during movement. The recorded couch positions in Aria do not reflect the actual treatment isocenter shift. Histories of treatment positions were collected for proton treatments of various sites consisting of Pelvis, Prostate, Breast, Head and Neck, Brain, and Abdomen along the couch longitudinal direction. A rigid-body transform was applied to these couch coordinates to determine the couch position in the treatment coordinate system. The transformed positions were compared to delta shifts assessed in Verity. Intrafraction variations of couch vertical position were compared before and after the correction.
Results: The 2-4 cm intrafraction variations of couch vertical position were observed for prostate and abdomen patients before the correction. This variation was reduced to within 5 mm after the correction. The comparison of the corrected vertical position with the Verity applied value demonstrated a mean residual error of less than 1 mm.
Conclusion: A rigid-body transform was applied to correct the recorded 6DoF robotic couch position. Large variation of couch vertical position is mainly attributed to the pitch angle applied and is dependent on relative target location along the couch longitudinal direction.
Keywords
Setup Verification, Image Guidance, Protons
Taxonomy
TH- RT Interfraction Motion Management: setup errors, immobilization, localization
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