Technical Note: Defining cyclotron-based clinical scanning proton machines in a FLUKA Monte Carlo system

Area of Science:

• Medical Physics
• Radiation Oncology
• Computational Science

Background:

• Cyclotron-based pencil beam scanning (PBS) proton therapy machines are prevalent but complex to model in Monte Carlo (MC) simulations due to energy degraders.
• Accurate MC simulation is crucial for verifying treatment plans generated by commercial treatment planning systems (TPS).

Purpose of the Study:

• To outline a generalized methodology for characterizing and simulating cyclotron-based PBS proton machines in a general-purpose MC code.
• To enable the generation of clinically relevant treatment plans using MC simulations derived from commercial TPS plans.
• To adapt MC codes for simulating cyclotron-based scanning proton machines for TPS verification and clinical plan improvement.

Main Methods:

• Characterized the beam from a cyclotron-based IBA Proteus Plus system at the Provision Proton Therapy Center using experimental commissioning data.
• Implemented the beam characterization in the FLUKA MC code.
• Validated the FLUKA model using experimental data in water phantoms for single beams and irregular fields, comparing results with RayStation TPS plans.

Main Results:

• MC simulations and TPS plans showed agreement in dose deposition within target areas.
• MC simulations exhibited lower differences in penumbrae at field edges compared to TPS.
• A gamma index of 3%/3 mm never dropped below 95%, indicating good agreement between MC and experimental data.

Conclusions:

• The developed FLUKA beam model accurately describes the experimental beam, demonstrating lower dose differences compared to TPS.
• The MC model can serve as a valuable tool for verifying and improving clinical proton therapy plans.
• The methodology provides a generalized approach for simulating cyclotron-based scanning proton machines in MC codes.