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Comparison of CyberKnife Multileaf Collimator and Fixed Cone: Treatment Planning Evaluation for Multiple Brain Metastasis

K Yang1*, S Sharma1 , J Yoon1 , S Stephenson2 , R McLawhorn3 , R Patel3 , A Ju1 , Y Feng1 , (1) East Carolina University, Greenville, NC, (2) Vidant Medical Center, Greenville, NC, (3) 21st Century Oncology, Greenville, NC


(Wednesday, 7/17/2019) 9:30 AM - 10:00 AM

Room: Exhibit Hall | Forum 1

Purpose: Multileaf collimator (MLC) has been introduced with CyberKnife M6 system, and it opens up the MLC application using its intensity modulation capability. We evaluated the treatment plan outcomes for multiple brain metastasis cases by comparing MLC and fixed cone.

Methods: In this study, eight patients with 2-3 brain metastases were selected whether using MLC can be a better clinical option. 25–30 Gy with 5 fractions were prescribed to the targets. MLC plans were optimized by finite size pencil beam (FSPB) and fixed cone plans by Ray Tracing, respectively, using Accuray Precision version Total MUs, treatment time, DVHs, dose distribution, Homogeneity Index (HI) and Conformity Index (CI) for GTV were analyzed. We also investigated the capability of MLC to reduce dose to organ at risk (OAR) located around the lesions.

Results: Mean dose to target and target coverage were similar between MLC and cone plans. MLC plans kept comparable dose homogeneity and conformality (mean HI for MLC and cone was 1.24 and 1.33; mean CI for MLC and cone was 1.58 and 1.62). For all cases, MLC plans offered a significant reduction in treatment time (43% on average), number of beams, and total MU (75% on average). With OAR adjacent to targets, MLC plan slightly lowered mean and maximum dose to critical structures compared with fixed cone. We also performed pre-treatment QA on MLC plans using ion chamber and EBT2 film. The results showed good agreement (>95%) at 3%/3mm.

Conclusion: This study demonstrated that MLC and fixed cone can produce similar planning quality for brain metastasis treatment, while MLC plans can be less time consuming and deliver less MUs.


Radiation Therapy, Brain, Treatment Planning


TH- External beam- photons: cyberknife

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