An algorithmic approach to single‐probe Cherenkov removal in pulsed x‐ray beams

Abstract

Purpose: The removal of Cherenkov light in an optical dosimetry system is an important process to ensure accurate dosimetry without compromising spatial resolution. Many solutions have been presented in the literature, each with advantages and disadvantages. We present a methodology to remove Cherenkov light from a scintillator fiber optic dosimeter in a pulsed megavoltage x-ray beam using the temporal waveform across the pulse. Methods: A sample waveform of Cherenkov light can be measured by exposing only the fiber to the beam. By assuming that the Cherenkov waveform closely matches the intensity of incident radiation, this waveform can be convoluted with the instantaneous scintillation response function to generate an expected scintillation signal. By finding the least-squares fit between these two functions and the experimental data, the estimated Cherenkov contribution can be subtracted off the net signal. This can be applied for arbitrarily complex Cherenkov waveforms (within the 2 ns timing resolution of the data acquisition), and in fact, the results suggest more fluctuations in the waveforms provide a better fit to data. Results: Four beam profiles for different field sizes and energies were found with this method. They closely matched references data measured with ionization chamber with average differences across the beam no more than 4%. Noisy waveforms are assumed to be the primary cause of differences between the analyzed scintillator and IC results. We propose methods for improving the results and optimizing the data acquisition and analysis processes. Conclusions: These results demonstrate that it is possible and effective with a single probe to use function fitting of expected data to experimental to remove a complicated Cherenkov signal from the net light signal in pulsed-beam optical dosimetry.

Advances on inorganic scintillator-based optic fiber dosimeters

“…However, the long decay time of some scintillators relative to the Cherenkov effect has also inspired solutions for eliminating the Cherenkov interference. For example, the BC-444 scintillator (Saint-Gobain Crystals) was chosen by Archer et al [49] to fabricate a PSFD because of its slow rise and decay time compared to the Cherenkov effect. They applied an algorithm-based temporal Cherenkov removal technique to eliminate Cherenkov interference.…”

Temporal modelling of beryllium oxide ceramics’ real-time OSL for dosimetry with a superficial 140 kVp X-ray beam

“…In recent work with plastic scintillation dosimeters, temporal kinetic modelling was applied to derive the expected scintillation, S(t), in response to some time dependent dose-rate Ḋ(t) [22]. It was found that the expected scintillation was proportional to the mathematical convolution of the dose-rate as a function of time, Ḋ(t), and an exponential rise and decay that is characteristic of the plastic scintillator [22]. Similarly, the measured rtOSL signal is dependent on a time dependent dose-rate, Ḋ(t), hence the same technique is applicable for rtOSL.…”

Technical note: Angular dependence in fiber optic dosimetry using YVO4:Eu3+

“…The stem effect adds to the radioluminescence (RL) signal, producing a bias in the dose rate measurement. Several methods have been put forward to reduce the stem effect, which are useful in different situations 17 . The time‐gated technique is suitable for filtering the short‐lived Cherenkov signal in LINACs when the scintillator features a long decay time of its RL signal of the order of 1 ms 18 .…”