Water equivalent phantom materials for ¹⁹²Ir brachytherapy

Area of Science:

• Medical Physics
• Radiation Oncology
• Materials Science

Background:

• Brachytherapy utilizes radioactive sources like Iridium-192 ((192)Ir) for targeted radiation therapy.
• Accurate dose calculations in brachytherapy require phantom materials that precisely mimic water's dosimetric properties.
• Evaluating the water equivalence of solid phantom materials is essential for reliable brachytherapy quality assurance.

Purpose of the Study:

• To assess the suitability of various solid phantom materials as water substitutes for (192)Ir brachytherapy dosimetry.
• To quantify the water equivalence of different phantom materials by comparing radial dose profiles.
• To identify phantom materials that maintain accuracy across a range of clinical distances.

Main Methods:

• Monte Carlo simulations using EGSnrc were performed to model photon fluence and absorbed dose distributions.
• Radial dose-to-water profiles in phantom materials were compared to those in water.
• Simulations considered varying phantom sizes and source-detector distances up to 30 cm.

Main Results:

• Materials like RW1, RW3, Solid Water, HE Solid Water, Virtual Water, Plastic Water DT, and Plastic Water LR showed excellent water equivalence (≤0.8% deviation) within 10 cm radii.
• Deviations increased for other materials (Original Plastic Water, Blue Water, polyethylene, polystyrene) up to 2.6% within 10 cm.
• At larger radii (up to 30 cm), deviations for the excellent materials remained below 1.4%, while others showed up to 8.1% deviation. PMMA showed <1% deviation at 30 cm.

Conclusions:

• The balanced content of inorganic additives in phantom materials is key for achieving water equivalence.
• Materials with excellent water equivalence are crucial for accurate brachytherapy dose measurements, especially at larger distances.
• The study provides a comprehensive comparison of solid phantom materials for (192)Ir brachytherapy dosimetry.