Program Information
Characteristics and Performance Evaluation of the First Commercial MLC for a Robotic Delivery System
C Fuerweger*1,2, P Prins1, H Coskan1, B Heijmen1, (1) Erasmus MC Cancer Institute, Rotterdam, The Netherlands, (2) European Cyberknife Center Munich, Munich, Germany
Presentations
SU-C-BRB-4 (Sunday, July 12, 2015) 1:00 PM - 1:55 PM Room: Ballroom B
Purpose: To assess characteristics and performance of the "Incise™" MLC (41 leaf pairs, 2.5mm width, FFF linac) mounted on the robotic SRS/SBRT platform "CyberKnife M6™" in a pre-clinical 5 months (11/2014-03/2015) test period.
Methods: Beam properties were measured with unshielded diodes and EBT3 film. The CyberKnife workspace for MLC was analyzed by transforming robot node coordinates (cranial / body paths) into Euler geometry. Bayouth tests for leaf / bank position accuracy were performed in standard (A/P) and clinically relevant non-standard positions, before and after exercising the MLC for 10+ minutes. Total system and delivery accuracy were assessed in End-to-End tests and dosimetric verification of exemplary plans. Stability over time was evaluated in Picket-Fence- and adapted Winston-Lutz-tests (AQA) for different collimator angles.
Results: Penumbrae (80-20%, with 100%=2*dose at inflection point; SAD 80cm; 10cm depth) parallel / perpendicular to leaf motion were 2.87/2.64mm for the smallest (0.76x0.75cm²) and 5.34/4.94mm for the largest (9.76x9.75cm²) square field. MLC circular field penumbrae exceeded fixed cones by 10-20% (e.g. 60mm: 4.0 vs. 3.6mm; 20mm: 3.6 vs. 2.9mm). Interleaf leakage was <0.5%. Clinically accessible workspace with MLC covered (non-coplanar) gantry angles of [-113°;+112°] (cranial) and [-108°;+102°] (body), and collimator angles of [-100°;+107°] (cranial) and [-91°;+100°] (body). Average leaf position offsets were ≤0.2mm in 14 standard A/P Bayouth tests and ≤0.6mm in 8 non-standard direction tests. Pre-test MLC exercise increased jaggedness (range ±0.3mm vs. ±0.5mm) and allowed to identify one malfunctioning leaf motor. Total system accuracy with MLC was 0.39±0.06mm in 6 End-to-End tests. Picket-Fence and AQA showed no adverse trends during the test period.
Conclusion: The Incise™ MLC for CyberKnife M6™ displayed high accuracy and mechanical stability over the test period. The specific CyberKnife geometry and performance after exercise demand dedicated QA measures.
Funding Support, Disclosures, and Conflict of Interest: This work is in part funded by a research grant from Accuray Inc, Sunnyvale, USA. Erasmus MC Cancer Institute also has research collaborations with Elekta AB, Stockholm, Sweden. C Fuerweger has previously received speaker honoraria from Accuray Inc, Sunnyvale, USA.
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