A tomographic reconstruction algorithm for cross-sectional imaging of IMRT beams from six projections

Area of Science:

• Medical Physics
• Radiation Oncology
• Image Reconstruction

Background:

• Patient-specific Quality Assurance (QA) is crucial for safe radiotherapy.
• Intensity Modulated Radiation Therapy (IMRT) presents QA challenges, especially for small fields.
• Scintillating fiber detectors offer potential for small field dosimetry.

Purpose of the Study:

• To develop and validate a novel method for reconstructing MLC-shaped small irradiation fields from limited projections.
• To assess the accuracy and error detection capabilities of the proposed reconstruction technique.

Main Methods:

• A tomographic reconstruction approach using a steepest descent algorithm to estimate geometric parameters from six projections.
• Validation using simulated data, radiochromic film measurements, and treatment planning system (TPS) data.
• Evaluation of error detection for dose, field location, and field shape deviations.

Main Results:

• High gamma analysis pass rates (e.g., 95.7% for 2%/1 mm criteria) comparing reconstructed and film-measured dose distributions for IMRT segments.
• Excellent agreement with TPS-provided data for smaller IMRT segments (e.g., 92.6% for 2%/1 mm criteria).
• The method successfully detected simulated delivery errors, including dose deviations and field shifts.

Conclusions:

• The developed method enables accurate tomographic reconstruction of IMRT segments using scintillating fiber projections.
• This technique is suitable for real-time, water-equivalent QA of small IMRT fields.
• The approach enhances the safety and efficiency of radiotherapy delivery through improved error detection.