Calculation of dose decrease in a finite phantom of a 192Ir point source

Area of Science:

• Medical Physics
• Radiotherapy Physics
• Computational Dosimetry

Background:

• Accurate dose calculation is crucial in brachytherapy.
• Existing algorithms may overestimate dose near phantom surfaces.
• Iridium-192 sources are commonly used in brachytherapy.

Purpose of the Study:

• To develop and validate a new algorithm for calculating dose decrease from an iridium-192 point source in a finite phantom.
• To compare the new algorithm's results with experimental measurements and Monte Carlo simulations.

Main Methods:

• A novel algorithm based on field theory and the 'mirror image' principle was developed.
• Measurements were performed in a water phantom using three experimental setups.
• Monte Carlo simulations were conducted to model dose distribution.

Main Results:

• The new algorithm demonstrated excellent agreement with measured data (within 0.9%) and Monte Carlo simulations (within 2%).
• The 'mirror source' strength was determined to be -0.103 of the real source.
• A lack scatter function was essential for accurate calculations near the surface.

Conclusions:

• The new field theory-based algorithm accurately calculates dose decrease for iridium-192 sources in finite phantoms.
• This algorithm offers a potential improvement over existing methods, reducing the risk of tumor underdosing.
• Further validation is needed for complex boundary shapes encountered in brachytherapy.