Technical note: A fast and accurate analytical dose calculation algorithm for ¹²⁵ I seed-loaded stent applications.

Area of Science:

• Medical Physics
• Radiation Oncology
• Interventional Radiology

Background:

• Portal vein tumor thrombosis (PVTT) treatment utilizes Iodine-125 (¹²⁵I) seed-loaded stents.
• Accurate dosimetry is crucial for optimizing and evaluating ¹²⁵I seed-loaded stent treatments.
• Current dosimetric characterization and fast dose calculation methods for these stents are lacking.

Purpose of the Study:

• To develop a fast and accurate analytical dose calculation method for ¹²⁵I seed-loaded stents.
• To incorporate the dosimetric effects of the stent and tissue inhomogeneity into the calculation.
• To provide a tool for treatment plan optimization and evaluation in PVTT management.

Main Methods:

• A detailed 3D model of the ¹²⁵I seed-loaded stent was created for Monte Carlo (MC) simulations.
• Dose perturbation kernels (DPKs) were derived to quantify stent-induced dose changes.
• The AAPM TG-43 formalism was adapted with DPKs and inhomogeneity correction factors (ICFs) for analytical dose calculation (TG-43-DP-ICF).

Main Results:

• The stent significantly perturbs dose, reducing it by up to 47.2% (single-seed) and 11.9%-16.1% (16-seed).
• The TG-43-DP-ICF method showed good agreement with MC simulations (error < 3.3% in water, < 5% in CT phantoms).
• TG-43-DP-ICF calculations were significantly faster (17 seconds) compared to full MC (25 hours).

Conclusions:

• The combination of DPKs and ICFs effectively addresses stent presence and tissue heterogeneity.
• The proposed TG-43-DP-ICF method offers both accuracy and computational efficiency.
• This method is suitable for dose evaluation and optimization in ¹²⁵I seed-loaded stent brachytherapy planning.