MCPI: a sub-minute Monte Carlo dose calculation engine for prostate implants

Area of Science:

• Medical Physics
• Computational Biology
• Radiotherapy Oncology

Background:

• Accurate dose calculation is critical for effective prostate brachytherapy.
• Traditional methods can be computationally intensive, limiting real-time treatment planning.
• Accounting for tissue heterogeneity and seed interactions is essential for precise dosimetry.

Purpose of the Study:

• To develop and validate an accelerated Monte Carlo code (MCPI) for rapid and accurate dose calculation in prostate brachytherapy.
• To assess the impact of interseed attenuation, tissue composition, and calcifications on dose distribution.
• To enable sub-minute dose calculations for improved treatment planning and assessment.

Main Methods:

• Developed MCPI, an accelerated Monte Carlo code simulating radioactive seeds in a 3D heterogeneous phantom.
• Employed a hybrid geometry model for rigorous treatment of interseed attenuation and tissue heterogeneity.
• Benchmarked MCPI against MCNP5 for 103Pd and 125I seeds, evaluating speed and accuracy.
• Quantified dosimetric effects of various factors using MCPI simulations.

Main Results:

• MCPI achieves dose calculations over 1000 times faster than MCNP5 for prostate brachytherapy.
• Calculations for a 103Pd implant (83 seeds) completed in 59 seconds with 2% uncertainty.
• Ignoring interseed attenuation or minor tissue variations can decrease D100 by 6%.
• Prostate calcifications (1%-5% volume) significantly reduce D80, D90, and D100 by up to 58%.

Conclusions:

• Sub-minute dose calculations are feasible for prostate brachytherapy using the MCPI code.
• MCPI accurately accounts for critical dosimetric effects, including interseed attenuation and tissue heterogeneity.
• The code facilitates more precise dose planning and assessment, potentially improving patient outcomes.