Developing and characterizing MR/CT-visible materials used in QA phantoms for MRgRT systems.

Area of Science:

• Medical Physics
• Radiotherapy Technology
• Materials Science

Background:

• Current synthetic tissue equivalent (STE) materials for radiotherapy QA phantoms lack magnetic resonance (MR) imaging visibility.
• This limitation hinders end-to-end quality assurance (QA) for MR-guided radiotherapy (MRgRT) modalities.

Purpose of the Study:

• To characterize dual MR/CT-visible STE materials for MRgRT QA phantoms.
• To identify suitable replacements for current non-visible STE materials.

Main Methods:

• Investigated MR, CT, and dosimetric properties of over 80 STE materials.
• Materials were scanned using MR (T1/T2-weighted) and CT (Hounsfield units, electron density).
• Dosimetric properties were assessed using EBT3 film in a custom phantom irradiated with a 6 MV beam.

Main Results:

• Silicone, hydrocarbon, synthetic gelatin, and liquid PVC plastic-based materials demonstrated good MR contrast.
• MR/CT-visible materials exhibited comparable CT attenuation to relevant tissues.
• Percent depth dose (PDD) curves of selected materials were comparable to conventional STE materials, with minor discrepancies at smaller field sizes.

Conclusions:

• Gelatin, liquid plastic, and hydrocarbon-based materials are viable alternative STE materials.
• These materials can be used in MRgRT QA phantoms for improved visualization and QA.
• The study successfully identified MR/CT-visible materials for advanced radiotherapy QA.