A Monte-Carlo method for interface dosimetry of beta emitters

Area of Science:

• Medical Physics
• Radiation Oncology
• Computational Dosimetry

Background:

• Accurate dose estimation is crucial for optimizing biologically targeted radiotherapy, especially at interfaces between different materials.
• Dose perturbations at these interfaces can significantly impact therapeutic outcomes.
• Understanding these perturbations requires detailed investigation across various parameters.

Purpose of the Study:

• To investigate electron dose perturbations at interfaces between materials with varying atomic numbers (Z) and water.
• To quantify the backscatter dose factor (BSDF) as a function of Z, energy, distance from the interface, and geometry.
• To develop empirical functions for correcting dose calculations in heterogeneous media.

Main Methods:

• Development of a Monte Carlo code using EGSnrc transport routines for absorbed dose distribution estimation in voxel geometry.
• Simulation of electron dose perturbations at interfaces with materials up to Z=79 (gold).
• Estimation of the backscatter dose factor (BSDF) across a range of energies, atomic numbers, and geometries.

Main Results:

• The BSDF magnitude varied from approximately 3% to 50%, depending on source energy and material's atomic number (Z).
• BSDF decreased with increasing electron energy and showed a logarithmic dependence on Z.
• BSDF was found to be highly sensitive to interface geometry and the scoring volume used.

Conclusions:

• The study provides essential data on electron dose perturbations at material interfaces relevant to radiotherapy.
• Developed empirical functions can aid in correcting dose calculations for heterogeneous scattering materials.
• The significant dependence of BSDF on geometry and scoring volume necessitates careful application of results to similar conditions.