A theoretical approach for non-equilibrium radiation dosimetry

Area of Science:

• Medical Physics
• Radiation Oncology
• Computational Dosimetry

Background:

• Accurate radiation dosimetry is crucial for effective cancer treatment.
• Small radiation fields, common in stereotactic radiosurgery, pose challenges for traditional dosimetry due to lack of charged-particle equilibrium (CPE).
• Existing methods struggle with precise dose determination in non-equilibrium conditions.

Purpose of the Study:

• To develop and validate a novel theoretical approach for radiation dosimetry in small and non-equilibrium fields.
• To apply the VMCBC algorithm for Monte Carlo-based dosimetry of megavoltage photon beams.
• To enable absolute and relative dosimetry in challenging scenarios like narrow stereotactic radiosurgery beams.

Main Methods:

• Developed and applied the VMCBC algorithm, a novel Monte Carlo technique.
• Modeled detailed geometry of accelerator heads and beam-defining systems.
• Utilized particle transport calculations to relate beam output to incident particles.
• Employed the BEAMnrc/DOSXYZnrc code for Monte Carlo simulations.

Main Results:

• Validated the VMCBC algorithm against experimental commissioning data for radiosurgery beams (7.5-30 mm diameters).
• Achieved agreement between Monte Carlo predicted beam outputs and experimental measurements within experimental uncertainties.
• Demonstrated the capability for absolute radiation dosimetry in regions without CPE.

Conclusions:

• The VMCBC Monte Carlo approach provides accurate absolute dosimetry for small, non-equilibrium radiation fields.
• This method overcomes limitations of experimental measurements in challenging clinical scenarios.
• The study validates a powerful new tool for radiation dosimetry in advanced radiotherapy techniques.