Phantom evaluation of a commercially available three modality image guided radiation therapy system

Area of Science:

• Medical Physics
• Radiotherapy Technology
• Image Analysis

Background:

• Image-guided radiation therapy (IGRT) relies on accurate imaging and image registration for precise tumor targeting.
• Varian linear accelerators offer various imaging modalities for IGRT, necessitating thorough evaluation of their performance.

Purpose of the Study:

• To comprehensively evaluate the imaging and image registration capabilities of Varian linear accelerators for IGRT.
• To assess the spatial resolution and accuracy of different imaging systems and registration software.

Main Methods:

• Modulation transfer function (MTF) curves were generated for megavoltage planar, kilovoltage (kV) planar, and cone beam computed tomography (CBCT) imaging systems.
• A phantom study was conducted to characterize image registration software accuracy and precision across three orthogonal directions.
• Performance was compared against conventional computed tomography (CT) and established benchmarks.

Main Results:

• Kilovoltage (kV) planar imaging demonstrated the highest spatial resolution among IGRT systems.
• All evaluated IGRT imaging techniques were deemed adequate for their intended clinical applications.
• Image registration software showed high accuracy, with kV planar imaging and automatic registration achieving sub-millimeter precision (approximately 1 mm).

Conclusions:

• The accuracy of IGRT using Varian equipment is primarily limited by couch readout resolution rather than imaging or registration software limitations.
• Current IGRT technology accuracy and precision surpass that of manual contouring in radiation therapy planning.
• The findings support the clinical utility and reliability of Varian's IGRT imaging and registration systems.