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Program Information

Physics Evaluation of a Newly Released InCise™
Multileaf Collimator for CyberKnife M6™

L Wang

L Wang*, E Chin , A Lo , Stanford University Cancer Center, Stanford, CA


SU-F-T-481 (Sunday, July 31, 2016) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose:This work reports the results of the physics evaluation of a newly released InCiseâ„¢2 Multileaf Collimator (MLC) installed in our institution.

Methods:Beam property data was measured with unshielded diode and EBT2 films. The measurements included MLC leaf transmission, beam profiles, output factors and tissue-phantom ratios. MLC performance was evaluated for one month after commissioning. Weekly Garden Fence tests were performed for leaf / bank positioning in standard (A/P) and clinically relevant non-standard positions, before and after MLC driving exercises of 10+ minutes. Daily Picket Fence test and AQA test, End-to-End tests and dosimetric quality assurance were performed to evaluate the overall system performance.

Results:All measurements including beam energy, flatness and symmetry, were within manufacture specifications. Leaf transmission was 0.4% <0.5% specification. The values of output factors ranged from 0.825 (7.6 mm x 7.5 mm) to 1.026 (115.0 mm x 100.1 mm). Average beam penumbra at 10 cm depth ranged from 2.7mm/2.7mm(7.6 mm x 7.5 mm) to 6.0 mm/6.2mm(84.6 mm x 84.7 mm). Slight penumbra difference (<10% from average penumbra for fields >20 mm) was observed in the direction perpendicular to leaf motion due to the tilting of the leaf housing. Mean leaf position offsets was -0.08±0.07mm and -0.13 ± 0.08 for X1 and X2 leaf banks in 13 Garden Fence tests. No significant difference on average leaf positioning offsets was observed between different leaf orientations and before/after MLC driving exercises. Six End-to-End tests showed 0.43±0.23mm overall targeting accuracy. Picket-Fence and AQA showed stable performance of MLC during the test period. Dosimetric point dose measurements for test cases agreed with calculation within 3%. All film measurements on relative dose had Gamma (2%, 2mm) passing rate of >95%.

Conclusion:The Inciseâ„¢2 MLC for CyberKnife M6â„¢ was proven to be accurate and reliable, and it is currently in clinical use.

Funding Support, Disclosures, and Conflict of Interest: Stanford was one of the physics evaluation sites for the newly released InCise 2 MLC for Accuray Inc.

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