Dosimetric perturbations at high-Z interfaces with high dose rate (192)Ir source

Area of Science:

• Medical Physics
• Radiation Oncology
• Materials Science

Background:

• High dose rate (HDR) brachytherapy utilizes Iridium-192 ((192)Ir) sources for localized cancer treatment.
• Understanding dose perturbations near interfaces is critical for accurate radiation dosimetry.

Purpose of the Study:

• To investigate dose perturbations caused by high-atomic number (Z) materials within the treatment region of (192)Ir HDR sources.
• To quantify the dose perturbation factor (DPF) and its dependence on material Z and thickness.

Main Methods:

• Measurements using a parallel plate ion chamber with a 5 μm thick window to assess dose rates downstream of high-Z materials.
• Monte Carlo (MC) simulations to calculate dose rates upstream and downstream of high-Z interfaces (0.01–2 mm).
• Evaluation of DPF using various high-Z materials (Pb, Au, Ta, Sn, Cu, Fe, Ti, Al) with thicknesses of 0.1 mm and 1.0 mm.

Main Results:

• Dose perturbation factor (DPF) is dependent on the atomic number (Z) and thickness of the material.
• MC simulations showed significant dose increases downstream of 0.1 mm layers of high-Z materials (e.g., DPF of 3.73 for Pb, 3.42 for Au).
• Discrepancies between MC and experimental results were observed for Z ≥ 50 due to large DPF gradients, while agreement was found for Z ≤ 29.

Conclusions:

• Thin layers of high-Z materials (Z ≥ 50) near (192)Ir sources can induce substantial dose perturbations, leading to local overdosing in brachytherapy.
• These dose perturbations may offer a potential method for delivering higher localized doses to targeted tissues.
• Accurate dosimetry requires careful consideration of high-Z material interactions in (192)Ir brachytherapy planning.