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Building a Dose Verification Model for M6™ Cyberknife System Using Monte Carlo Simulation

T Neupane, C Shang, W Muhammad, T Leventouri, South Florida Proton Therapy Institute, Delray Beach, FL

Presentations

(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose:
In InCise™ II Multileaf Collimator (IMLC) equipped CyberKnife® Stereotactic Radiosurgery system (M6CK), the dose calculations particularly in heterogeneous media becomes more challenging due to many off-central-axis projected FFF beams from intensity-modulated MLC beamlets. Therefore, an independent and accurate dose verification is recommended to validate its treatment planning system. This research is to investigate the efficacy of Monte Carlo (MC) dose verification model for the treatment planning on M6CK system.

Methods:
The M6CK head including IMLC was modeled, based on detailed diagrams provided by Accuracy (Sunnyvale, CA) using the EGS-BEAMnrc simulation. The phase space files, for every particle crossing a scoring plane, were stored before and after IMLC and then fed into the DOSXYZnrc for dose simulations in a water phantom. A component module for IMLC was built by modifying the pre-existing MLC module to mimic IMLC design. We ran several simulations by increasing the number of initial histories, and analyzed the dose statistics including dose profiles and depth dose curves at 800mm Source to Axis Distance (SAD) in water phantom. The energy (6-7MeV) and Full Width Half-Maximum (FWHM) 1.8-2.4mm of incident electron beam were simulated. Dose profiles and depth dose curves for the open fields (53.8x53.9-7.6x7.7 mm2) between MC simulation and treatment planning (measurements) were compared to validate the MC model.


Results:
During MC simulation, incident electron beam energy 7MeV (equivalent to 6 MV photon beam) with a FWHM of 2.2mm was the best match with results from treatment planning and measurements. Preliminary results showed the dose uncertainties within 2% for all the open fields (53.8x53.9-7.6x7.7 mm2).


Conclusion:
: Good agreements for the dose profiles (= 2%) and dose outputs (= 3%) were found between the simulations and measurements at 800 mm SAD. Currently, we are working on potential implementation of our MC model in patient specific quality assurance.

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