An FFT-based beam profile denoising method for beam profile distortion correction

The accurate verification of beam parameters is mandatory for treatment safety in particle therapy, therefore, the systematic uncertainties of the segmented ionization chambers and detector arrays used as beam monitors, must be measured. In this study, a Fast Fourier Transform (FFT) based denoising method is proposed to remove noise from the pencil beam profile signal in both the spatial and spatial-frequency domains. In the spatial domain, the bias caused by noise was corrected, and the noise outside the 4σ range of the spot center was discarded. Then, in the spatial-frequency domain, thanks to the Gaussian shape of the signal’s magnitude spectrum, the 4σ range of frequency components was extracted to eliminate the signal fluctuation caused by noise. In addition, low amplitude high-frequency components are finely removed by thresholding to reduce the distortion of beam profile signals. The performance of the proposed method was verified through simulation experiments in terms of the coefficient of determination (R2) and signal-to-noise ratio (SNR). Results show that SNRs of the denoised signals are more than six times higher than those of the original signals and R2 of the denoised signals is larger than 0.9. The denoising capability of the presented method was verified by an X-ray radiation experiment. R2 of the denoised signal achieves 0.96 from 0.60, and the fitting errors of beam parameters (μ and σ) also decrease by denoising without increasing the radiation intensity and the integration time.