A component method to delineate surgical spine implants for proton Monte Carlo dose calculation

Area of Science:

• Medical Physics
• Radiotherapy
• Medical Imaging

Background:

• Metallic implants in spinal sarcoma and chordoma patients pose challenges for accurate radiotherapy planning.
• Uncertainty in delineating implants on computed tomography (CT) scans compromises proton Monte Carlo dose calculation (MCDC) accuracy.
• Accurate implant characterization is crucial for effective radiation dose delivery and patient outcomes.

Purpose of the Study:

• To develop and validate a component method for precise determination of metallic implant dimensions and volume from CT images.
• To improve the accuracy of proton Monte Carlo dose calculation (MCDC) in patients with spinal implants.
• To reduce uncertainties in radiotherapy planning and enhance treatment quality for spinal tumor patients.

Main Methods:

• A component method was developed, utilizing vendor-specific implant component knowledge (tulips, screw bodies, lockers, rods) for accurate contouring.
• Retrospective patient data and reference implant samples from medical records and vendors (Medtronic, NuVasive) were used.
• CT images with diverse features were analyzed to quantify implant contour uncertainties.

Main Results:

• The component method demonstrated significantly higher accuracy in implant volume estimation compared to conventional threshold methods.
• Differences in vivo were 0.35 cm³ (tulips), 0.17 cm³ (screw bodies), and 0.04 cm³ (rods) for the component method versus 5.46, 0.76, and 0.05 cm³ for the threshold method.
• Implant mischaracterization can lead to underdosing of up to 20 cm³ in clinical target volumes, with tulips contributing significantly to uncertainty due to varied materials.

Conclusions:

• The developed component method provides accurate implant characterization for proton MCDC, enhancing proton therapy treatment quality.
• This method shows promise for improving radiotherapy for spinal tumors, with potential future applications in cervical spine and dental implants.
• Further investigation into extending the method to other anatomical regions and implant types is warranted.