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Development of a Full Monte Carlo Therapeutic Dose Calculation Toolkit for Halcyon Using Geant4

R Liu1*, Z Ji2, B Cai3, G Hugo4, S Mutic5, T Zhao6, (1) Washington Univ. in St. Louis, St. Louis, MO, (2) Washington University St Louis, ,,(3) Washington University School of Medicine, St. Louis, MO, (4) Washington University School of Medicine, St. Louis, MO, (5) Washington University School of Medicine, Saint Louis, MO, (6) Washington University School of Medicine, St. Louis, MO

Presentations

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

Room: AAPM ePoster Library

Purpose: develop, implement a full Monte Carlo (MC) therapeutic dose calculation toolkit of Halcyon in Geant4 for achieving the second dose check for the vendor’s treatment planning system.


Methods: phase space files above the double stack MLC (DSMLC) were obtained using Varian’s cloud-based MC simulator, VirtualLinac. The DSMLC is modeled and the radiation transport through DSMLC and patient phantom was simulated using Geant4. The simulated and measured dose were first validated in a 3D water phantom using open fields with seven field sizes (2x2, 4x4, 6x6, 8x8, 10x10, 20x20, 28x28 cm2). The difference in percent depth dose (PDD) and beam profiles (BP) were quantified. The developed toolkit was also used to calculate the intensity-modulated radiation therapy (IMRT) plans of prostate and brain tumor with Halcyon beam model. 1D beam profile, 3D dose difference and 3D Gamma analysis were used to evaluate the discrepancy between our model and treatment planning system (Acuros, Eclipse 15.6).


Results: simulated BP and PDD in water phantom match well (±2%) with the measured ones for all field sizes. For the prostate and brain IMRT plans, the simulated dose showed a good agreement in both 1D and 3D dose distribution. The 3D gamma pass rate (3%/3mm) are 98.08% and 95.4% for prostate and brain plans respectively.


Conclusion: DSMLC used in Halcyon Linac was successfully modeled. The results from the full MC toolkit developed in this study showed a good agreement with measurements and TPS results.

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