Computed tomography sequence integration for enhanced proton therapy in patients with metallic implants.

Area of Science:

• Medical Physics
• Radiation Oncology
• Biomedical Imaging

Background:

• Metallic implants in patients undergoing proton therapy cause significant image distortions and dose calculation errors.
• Accurate imaging and dose calculation are crucial for effective and safe pencil beam scanning proton therapy, especially with metal artifacts.

Purpose of the Study:

• To evaluate single-energy CT (SECT), dual-energy CT (DECT) with iterative metal artifact reduction (IMAR), and megavoltage CT (MVCT) for optimizing imaging and dosimetry in proton therapy.
• To assess the geometric and dosimetric accuracy of different CT imaging protocols in the presence of metallic implants.

Main Methods:

• Phantom studies using titanium and cobalt alloy implants were performed with SECT (with MAR), DECT (with IMAR), and MVCT.
• DECT datasets were processed to generate virtual monoenergetic images (VMI), relative electron density (RED), and stopping power ratio (SPR) images.
• Geometric accuracy was evaluated using Dice similarity coefficient and Hausdorff distance; CT number calibration and proton range/dose accuracy were validated using film and ionization chambers.

Main Results:

• MVCT demonstrated the highest geometric fidelity (Dice = 0.89).
• SECT provided the most accurate density estimates for titanium and solid water.
• DECT with IMAR, using SPR or RED, achieved superior dose accuracy (γ>98%) and range accuracy (≈1.1 mm), with significant variations in range errors for complex implants (0.8 mm to 7.6 mm).

Conclusions:

• SPR or RED with IMAR enables accurate dose and range estimations for small titanium implants.
• For larger or high-Z implants, combining MVCT with SPR or RED (with IMAR) significantly improves treatment precision due to enhanced geometric and dosimetric accuracy.