Fast Monte Carlo simulation for total body irradiation using a (60)Co teletherapy unit

Area of Science:

• Medical Physics
• Radiotherapy
• Computational Dosimetry

Background:

• Total body irradiation (TBI) is a crucial radiotherapy technique.
• Current treatment planning systems have limitations in dose calculation accuracy for TBI.
• Accurate dose calculation is essential for optimizing TBI efficacy and minimizing toxicity.

Purpose of the Study:

• To develop and validate a fast Monte Carlo code for calculating dose distributions in TBI.
• To assess the accuracy of the developed code by comparing its results with experimental measurements and another simulation tool.
• To evaluate the potential of the Monte Carlo code as a clinical tool for TBI treatment planning.

Main Methods:

• A modified Theratron 780 60Co unit was used for TBI delivery.
• A C-based fast Monte Carlo code was developed, utilizing CT-derived voxel density for heterogeneous media.
• Dose calculations were validated using film-based measurements in water and RANDO phantoms, and compared with GEANT4 simulations.

Main Results:

• The Monte Carlo code accurately predicted the depth of maximum dose (0.5 cm) in a water phantom.
• Measured Percentage Depth Dose (PDD) closely matched Monte Carlo calculations, with an average deviation of 3%.
• Gamma analysis in the RANDO phantom showed high pass rates (>99% at 5mm, 5% criteria), with mean relative differences <2% for profiles.

Conclusions:

• The developed Monte Carlo algorithm is a viable method for calculating dose distributions in TBI treatments.
• The code provides clinically useful information for TBI planning, with calculations completed within hours.
• Further optimization could enable the Monte Carlo method as a first-line treatment planning option for 60Co TBI.