Author: Mohamed Eldib, Adam Mahl, Moyed Miften, Rachel Petragallo, Kelly L. Stuhr 👨🔬
Affiliation: University of Colorado - Anschutz Medical Campus, University of Colorado School of Medicine, University of Colorado Denver, Department of Radiation Oncology, University of Colorado 🌍
Purpose: To compare electron beam dose calculations performed manually with those computed using the Macro Monte Carlo simulation for standard fields on both phantom and patient setups, with the aim of identifying configurations where significant deviations occur between manual and Macro Monte Carlo calculations.
Methods: Manual and Monte Carlo simulations were performed to calculate the electron beam dose for standard fields on both phantom and patient models (abdomen, head, and head oblique), encompassing approximately 235 clinical scenarios. These scenarios involved various combinations of cone sizes, standard cutouts, beam energies, and source-to-surface distances (SSDs). The cone sizes utilized included 6×6, 10×10, 15×15, 20×20, and 25×25 cm², with circular and rectangular cutouts of varying dimensions. Beam energies ranged from 6 to 20 MeV , and SSDs spanned 100 to 120 cm at 5 cm intervals. All calculations were performed with a fixed source-to-axis distance (SAD) of 100 cm and a dose rate of 1000 MU/min. Two gantry setups were considered: one at 0° (perpendicular to the phantom or patient’s anterior surface) and the other at an oblique angle of 45°. Insert factors were experimentally determined for manual dose calculations. The Hounsfield Units (HU) were estimated using Macro Monte Carlo simulations and subsequently compared to values derived from manual calculations.
Results: Among the 235 setups evaluated, only 14 scenarios displayed relatively high deviations with absolute differences ranging between 10 and 17 HU.
Conclusion: This study demonstrates the robust applicability of macro Monte Carlo simulations for electron dosimetry in clinical settings, revealing strong agreement with minimal discrepancies, particularly for oblique gantry configurations and small cutouts.