Comparative Evaluation of Curve-fitting Techniques for Electronic Portal Imaging Device-based Multileaf Collimator Picket Fence Analysis
Vijay Kumar Mogulagani, Mohan Raj Uthiran, C. H. Raja Babu, Madhuri DumpalaPurpose:
The primary objective of this study was to identify the most suitable curve-fitting method for picket fence analysis by comparing commonly used mathematical fitting approaches with film-based reference measurements.
Materials and Methods:
A picket fence test was planned on an Elekta Synergy linear accelerator equipped with an MLCi2 multileaf collimator (40 leaf pairs) using 6-mm slit widths and five pickets with a nominal field geometry of 0.6 cm × 24 cm, covering 24 leaf pairs per picket. For analysis, only the central 20 opposing leaf pairs in each picket were evaluated, yielding a total of 100 analyzed peaks. The identical picket fence plan was delivered to both the electronic portal imaging device (EPID) and Gafchromic film. EPID images were exported as TIFF files and analyzed using PTW MEPHYSTO software to obtain peak coordinates, followed by manual determination of peak center position, maximum amplitude, and full width at half maximum (FWHM).
Results:
Mean FWHM values were 6.90 mm (Gaussian), 5.69 mm (Lorentzian), 6.29 mm (pseudo-Voigt), 6.92 mm (manual), and 6.56 mm (film). Gaussian fitting and manual measurements demonstrated systematic overestimation of FWHM relative to film, while Lorentzian fitting showed the largest deviation and highest root mean square error (RMSE).
Conclusion:
Based on percentage error, RMSE, and Bonferroni-corrected nonparametric statistical analysis, pseudo-Voigt curve fitting provides the most accurate and consistent estimation of slit width in EPID-based picket fence analysis.