Calculation of radiation dose at a bone-to-marrow interface using Monte Carlo modeling techniques (EGS4)

Area of Science:

• Medical Physics
• Radiation Biology
• Computational Modeling

Background:

• Understanding radiation dose distribution at the microscopic bone-marrow interface is crucial for internal radiation dosimetry.
• Isotopes used in targeted radionuclide therapy can deposit dose heterogeneously.
• Accurate dose calculations are essential for predicting therapeutic efficacy and toxicity.

Purpose of the Study:

• To calculate radiation dose rate profiles at the bone-to-marrow interface.
• To investigate the dose contribution from atomic electrons, beta, and photon fractions for specific isotopes.
• To assess the impact of backscatter on marrow dose.

Main Methods:

• Simulated uniform radiation sources at the endosteal layer of long bones.
• Utilized the Electron-Gamma Shower (EGS4) computer program for microscopic dose calculations.
• Assumed isotopes (153Sm, 186Re, 166Ho) assimilated as surface agents.
• Validated the computational model against published dose factors with >95% accuracy.

Main Results:

• Dose distributions revealed contributions from electrons, beta, and photons.
• Backscatter dose to marrow increased from 3-4% at the source to 6-8% at 100 microns depth.
• Backscattered dose fraction was similar across the three isotopes.
• Dose contributions from 153Sm, 186Re, and 166Ho were similar between 25 and 125 microns.

Conclusions:

• The computational model accurately predicts dose distributions at the bone-marrow interface.
• Backscatter plays a significant role in marrow dose, increasing with depth.
• The studied isotopes exhibit similar dose distribution characteristics, supporting their potential use in targeted therapies.