Remote sensing array (RSA) for linac beam monitoring

Area of Science:

• Medical Physics
• Radiation Oncology
• Detector Physics

Background:

• Accurate real-time monitoring of medical linear accelerator (linac) beams is crucial for safe and effective radiation therapy.
• Current methods may involve beam attenuation or lack real-time feedback on critical parameters like multileaf collimator (MLC) positions and dose rate.

Purpose of the Study:

• To evaluate the feasibility of a novel, non-attenuating, real-time beam monitoring device for medical linacs.
• To develop a theoretical concept for a detector geometry and physical model capable of determining MLC leaf positions and dose rate in real time.

Main Methods:

• A detector concept using opposing electrode arrays to sense charge carriers generated by the linac beam was proposed.
• The Shockley-Ramo theorem and method of images were used to model charge carrier detection.
• A Least-Squares approach was employed to solve the inverse problem for determining beam parameters from measured signals.
• Radiation transport simulations (1D CEPXS/ONEDANT) quantified detector sensitivity.

Main Results:

• The theoretical model demonstrated the feasibility of remotely sensing MLC leaf positions with sub-millimeter accuracy (0.25–1 mm).
• Signal amplitudes were estimated in the fA to pA range for a 6 MV linac pulse.
• Detector response was found to be dependent on MLC field shape and leaf position.

Conclusions:

• A computationally feasible concept for a remote sensing detector capable of real-time measurement of linac beam parameters (MLC positions, dose rate) was demonstrated.
• Future work should focus on optimizing electrode geometry for enhanced sensitivity and improving reconstruction algorithms for greater accuracy.