Monte Carlo Simulation for the Radixact™ Tomotherapy Linac Using EGSnrc.

Area of Science:

• Medical Physics
• Radiation Oncology
• Computational Modeling

Background:

• Accurate Monte Carlo (MC) simulations of linear accelerators require precise data on electron beam properties, which are often unavailable from manufacturers.
• This lack of information hinders the development of reliable MC models for treatment planning and verification.

Purpose of the Study:

• To forecast the incident electron beam's energy, radial intensity (spot size), and angular spread for a Radixact™ TomoTherapy Linac.
• To verify a developed MC-simulated linear accelerator model using experimental measurements.

Main Methods:

• Utilized the BEAMnrc code to simulate a 6 MV photon beam from a Radixact™ TomoTherapy Linac.
• Performed percentage depth dose and beam profile calculations using DOSYXZnrc, comparing them to measurements via the Gamma index.
• Fine-tuned electron energy, spot size, and angular spread to minimize discrepancies between simulated and measured data.

Main Results:

• The optimized MC model determined an electron beam energy of 5.8 MeV and a spot size of 1.4 mm.
• An average angular spread of 0.05 significantly reduced profile disparities, with 88.6% of points passing the 1%/1 mm Gamma test.
• Output factor discrepancies between the MC model and measurements were within 1.5%.

Conclusions:

• A reliable MC model for the Radixact™ TomoTherapy Linac was successfully created using the BEAMnrc code.
• This validated model can be confidently used for accurate dose distribution calculations in radiation therapy.