Performance of a Full-Scale Upstream MAPS-Based Verification Device for Radiotherapy.

Area of Science:

• Medical Physics
• Radiation Oncology
• Detector Technology

Background:

• Intensity-modulated radiotherapy (IMRT) requires precise beam shaping for accurate tumor targeting.
• Real-time, independent verification of radiation beams is crucial for safe and effective IMRT.
• Monolithic Active Pixel Sensors (MAPS) show promise for upstream beam monitoring during radiotherapy.

Purpose of the Study:

• To evaluate the performance of a large-scale MAPS demonstrator system for real-time radiotherapy beam monitoring.
• To assess the feasibility of using a 2x2 MAPS matrix to cover typical radiotherapy treatment fields.
• To develop and validate a position algorithm for reconstructing leaf positions across the sensor matrix.

Main Methods:

• Construction of a 2x2 matrix of MAPS, designed to fit on a LINAC shadow tray.
• Implementation of a novel position algorithm to reconstruct leaf positions from sensor data.
• Measurement of position resolution across the sensor matrix, including areas between sensors.
• Estimation of dose error based on the achieved leaf position resolution.

Main Results:

• The 2x2 MAPS matrix is sufficiently large to cover most radiotherapy treatment fields.
• A newly developed position algorithm achieves a position resolution below ~200 μm in sensor centers.
• Position resolution degrades to just below 300 μm in the gaps between sensors.
• The achieved leaf position resolution leads to an estimated dose error below 2%.

Conclusions:

• The large-scale MAPS demonstrator system meets clinical requirements for real-time radiotherapy beam monitoring.
• The developed position algorithm effectively reconstructs leaf positions, even across sensor gaps.
• The system's performance, with a dose error below 2%, is suitable for clinical deployment in IMRT.