Comparative Evaluation of Curve-fitting Techniques for Electronic Portal Imaging Device-based Multileaf Collimator...

Area of Science:

• Medical Physics
• Radiation Oncology
• Image Analysis

Background:

• Accurate measurement of radiation beam characteristics is crucial for quality assurance in radiotherapy.
• The picket fence test is a standard method for evaluating the performance of multileaf collimators (MLCs).
• Electronic Portal Imaging Devices (EPIDs) are increasingly used for in-vivo dosimetry and quality assurance.

Purpose of the Study:

• To determine the optimal curve-fitting method for picket fence analysis using EPID data.
• To compare the accuracy of different mathematical fitting approaches against film-based measurements.

Main Methods:

• A picket fence test was performed on an Elekta Synergy linear accelerator with an MLCi2.
• EPID and Gafchromic film were used to acquire data for identical picket fence plans.
• Peak coordinates, amplitude, and full width at half maximum (FWHM) were analyzed using various fitting methods (Gaussian, Lorentzian, pseudo-Voigt, manual) and compared to film.

Main Results:

• Pseudo-Voigt fitting yielded a mean FWHM of 6.29 mm, closely matching the film reference of 6.56 mm.
• Gaussian fitting and manual measurements overestimated FWHM compared to film.
• Lorentzian fitting showed the largest deviation and highest root mean square error (RMSE).

Conclusions:

• Pseudo-Voigt curve fitting provides the most accurate and consistent estimation of slit width in EPID-based picket fence analysis.
• This method is recommended for improving the reliability of MLC performance evaluation using EPIDs.