Dose verification with Monte Carlo technique for prostate brachytherapy implants with (125)I sources

Area of Science:

• Medical Physics
• Radiation Oncology
• Computational Biology

Background:

• Brachytherapy, particularly with iodine-125 ((125)I) seeds, is a common treatment for prostate cancer.
• Accurate dose distribution calculation is critical for treatment efficacy and minimizing side effects.
• Current treatment planning systems (TPS) often rely on approximations that may impact dose accuracy.

Purpose of the Study:

• To implement the Monte Carlo (MC) technique for calculating dose distributions in a model prostate brachytherapy implant.
• To compare MC-derived dose distributions with those from a commercial TPS (VariSeed).
• To evaluate the impact of TPS approximations on dose coverage and identify areas for improvement.

Main Methods:

• Monte Carlo simulation was used to model dose distributions from (125)I brachytherapy sources in a prostate phantom.
• Calculated dose distributions were compared against a commercial TPS, VariSeed.
• Dose-volume histograms (DVHs) were analyzed to quantify differences in isodose line coverage.

Main Results:

• The commercial TPS provided 100% prostate coverage at the prescription dose when using MC-derived source strength.
• VariSeed showed significantly larger dose coverage for 150% (29% increase) and 200% (136% increase) isodose lines compared to MC simulations.
• Differences were attributed to the point source approximation and neglected interseed effects in the commercial TPS.

Conclusions:

• Monte Carlo simulations provide more accurate dose calculations in (125)I prostate brachytherapy compared to conventional TPS.
• The point source approximation and neglect of interseed effects in current TPS lead to discrepancies in high-dose coverage.
• Implementing MC techniques in TPS is recommended for enhanced accuracy in brachytherapy dose planning.