Heavy metal in radiation therapy: A simple method to differentiate hip prosthesis materials

Area of Science:

• Medical Physics
• Radiotherapy
• Biomedical Engineering

Background:

• Increasing use of radiation therapy for hip replacement patients.
• Need for accurate dose calculation near metal implants.
• Limitations of current metal artifact reduction techniques.

Purpose of the Study:

• Identify hip prosthesis materials (titanium and stainless steel).
• Improve accuracy of radiation dose calculations.
• Correctly assign implant materials in treatment planning systems.

Main Methods:

• Verified CT mass density calibration curves for titanium (Ti) and stainless steel (SS) inserts.
• Developed an interpolation-based method to differentiate Ti and SS materials.
• Validated the method on patient data using two Siemens reconstruction kernels (Br44f and Sd40f).

Main Results:

• Hounsfield units (HU) varied significantly with insert diameter, CT spectrum, and reconstruction kernels due to artifacts.
• Extended CT-density calibration curves are not recommended for heavy metal density determination.
• The interpolation method achieved 100% detection and material differentiation for stems and high accuracy for heads and acetabular cups.

Conclusions:

• The developed method reliably differentiates hip prosthesis materials (Ti vs. SS) without prior knowledge.
• Enables excellent dosimetric accuracy with advanced dose algorithms (Acuros XB, Monte Carlo).
• Method is adaptable to different CT units and reconstruction kernels, replacing extended CT-density calibration curves.