An Analytical Microdosimetric Model for Radioimmunotherapeutic Alpha Emitters

Area of Science:

• Medical Physics
• Radiation Oncology
• Nuclear Medicine

Background:

• Targeted radiotherapy with alpha particles offers high radiobiological effectiveness.
• Accurate microdosimetric calculations are crucial for optimizing alpha particle therapy.
• Existing methods often rely on computationally intensive simulations.

Purpose of the Study:

• To develop an analytical methodology for determining microdosimetric quantities in alpha particle radiotherapy.
• To model energy imparted and its distribution in microscopic sites.
• To enable accurate calculations for polyenergetic alpha particle sources.

Main Methods:

• Utilized Monte Carlo simulations with the Geant4-DNA toolkit for monoenergetic alpha particles.
• Developed analytical functions fitted to simulation data for energy imparted and variance.
• Applied the methodology to a radioimmunotherapy model of a cell with an alpha-emitting source and a central nucleus.

Main Results:

• The analytical method accurately predicted mean and dose-mean specific energy (z) and lineal energy (y).
• Agreement with Geant4-DNA simulations was within 4% for 1-µm and 5-µm nuclei, improving to 1% for dose-mean values.
• Discrepancies for 10-µm nuclei were approximately 9% for mean values and 3% for dose-mean values, within simulation uncertainties.

Conclusions:

• The developed analytical method provides accurate microdosimetric calculations for alpha particle radiotherapy.
• This approach can be used to characterize the radiobiological effectiveness of targeted therapies.
• The methodology requires knowledge of spatial source and target distributions for microdosimetric quantity calculation.