Intensity-modulated brachytherapy for vaginal cancer

Area of Science:

• Medical Physics
• Radiation Oncology
• Monte Carlo Simulation

Background:

• Vaginal cancer treatment often involves brachytherapy, with intensity-modulated brachytherapy (IMBT) offering potential for dose optimization.
• Conventional applicators may have limitations in precise dose modulation, necessitating exploration of advanced applicator designs.

Purpose of the Study:

• To evaluate the dose modulation capabilities of static and dynamic steel-shielded applicators for vaginal cancer IMBT.
• To compare the performance of steel-shielded applicators against conventional Plexiglas applicators in terms of target coverage and organ at risk (OAR) sparing.

Main Methods:

• Utilized the Geant4 Application for Emission Tomography (GATE) Monte Carlo code (version 9.0) for simulations.
• Modeled vaginal cancer IMBT in a pelvic water-equivalent phantom using static and dynamic steel-shielded applicators, and a conventional Plexiglas applicator.
• Simulated irradiation using Cobalt-60 (⁶⁰Co) and Iridium-192 (¹⁹²Ir) high-dose-rate seeds, calculating absorbed doses to target and OARs.

Main Results:

• Dynamic IMBT with steel-shielded applicators significantly reduced the D_2cc of the rectum and bladder (up to 40% with ¹⁹²Ir).
• Static IMBT with steel-shielded applicators also demonstrated OAR sparing (up to 22.21% for rectum, 17.71% for bladder with ¹⁹²Ir).
• All three techniques maintained comparable target coverage, with mean relative variations of absorbed dose parameters (D₅, D₉₀, D₁₀₀) within 0.96%.

Conclusions:

• Static and dynamic steel-shielded applicators provide superior OAR protection compared to conventional applicators in vaginal cancer IMBT.
• These advanced applicators effectively spare organs at risk while ensuring adequate target dose coverage.
• Steel-shielded applicators represent a promising advancement for improving treatment efficacy and safety in vaginal cancer brachytherapy.