SU-E-J-02: Accuracy of Fiducial Marker Localization Using Axial and Helical CT, Cone-Beam CT and KV Imaging

Area of Science:

• Medical Imaging Physics
• Radiation Oncology

Background:

• Accurate localization of implanted fiducial markers is critical for image-guided radiation therapy (IGRT).
• CT imaging parameters, including slice thickness and motion, can introduce localization errors.

Purpose of the Study:

• To evaluate localization errors of fiducial markers using various CT imaging modalities.
• To assess the impact of slice thickness and motion on marker accuracy in axial (ACT), helical CT (HCT), cone beam CT (CBCT), and kV imaging.

Main Methods:

• A thorax phantom with fiducial markers of varying sizes (2.5-20mm) was imaged using ACT, HCT, CBCT, and kV imaging.
• Scans were performed with and without simulated motion (15mm amplitude, 15 cycles/min).
• CT images were reconstructed at different slice thicknesses (0.625-5mm), and marker location and length were measured.

Main Results:

• Increased slice thickness enlarged apparent marker size and displaced marker centers in ACT and HCT.
• Phantom motion further increased marker size and center displacement, with HCT showing more prominent shifts.
• kV imaging provided the sharpest marker images with minimal size discrepancies compared to actual marker dimensions.

Conclusions:

• Slice thickness and motion introduce significant fiducial marker localization errors in ACT and HCT.
• These distortions necessitate careful consideration in CT-based IGRT for precise tumor localization and patient positioning.
• kV imaging demonstrates superior accuracy for fiducial marker visualization in IGRT applications.