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Use of VirtuaLinac to Perform Monte-Carlo Based Dose Calculation for Verification of Radiotherapy Treatments On a Jawless Ring Gantry Linac with Double Stack MLC

A Sethi1*, Z Ji1, R Liu1, E Laugeman1, D Sawkey2, T Zhao1, S Mutic1, G Hugo1, B Cai1, (1) Washington University School of Medicine, St. Louis, MO, (2) Varian Medical Systems, Palo Alto, CA

Presentations

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

Room: AAPM ePoster Library

Purpose: VirtuaLinac (VL) platform developed by Varian Medical Systems® is a Monte-Carlo (MC) calculation package capable of simulating interactions in a linac treatment head and the dose deposition in a virtual phantom or CT dataset. VL runs on Amazon Web Services (AWS) cloud network providing enhanced computation power. Here we aim to demonstrate VL’s ability to perform MC-dose calculation to verify plan fidelity from a newly released ring gantry linac, Halcyon, with double stack MLC and 6MV FFF beam.

Methods: A workflow was established using VL via AWS with plan, structure and CT dataset as input and VL calculated MC dose as output. Multiple Halcyon plans were generated using Eclipse TPS for comparison. Validation cases included static fields on a virtual water phantom and TG-119 plans with dynamic MLC on a solid water phantom. For each plan, XML files with MLC positions, gantry angle, and collimator were used as input to the VL. 1D beam profiles, dose differences and 3D gamma passing rate (3%/3mm) were used as evaluation metrics to access plan fidelity.

Results: All cases were successfully simulated, and the 1D profiles in both directions matched well. For open field calculation on water phantom, 3D Gamma was 94.3%, 98.2%, 99.2% for a 4x4, 10x10, and 28x28 cm² field size respectively. Simulations with an AP/PA, AP3S (dynamic MLC with 3 segments), and four-field box resulted in a Gamma of 93.6%, 97.6%, 93.9%. A 9-beam Head-Neck IMRT plan generated a 95.0% Gamma. Simulations on the TG119 phantom included AP beam (93.0%), AP/PA beam (93.0%) and AP3S (92.3%).

Conclusion: The VL represents the first MC simulation and modeling for the Halcyon linac and is a promising comparison tool for TPS dose calculation. Our future work will optimize simulation resources and plan accuracy aimed to translate VL into clinical workflow.

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Funding Support, Disclosures, and Conflict of Interest: Research supported by Varian Medical Systems

Keywords

Monte Carlo, Validation, Dose

Taxonomy

Not Applicable / None Entered.

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