Temporally separating Cherenkov radiation in a scintillator probe exposed to a pulsed X-ray beam

Madden

et al. 2019

Medical Physics

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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.

“…The scintillator sensitive volume is a cylinder 0.5 mm long and 1 mm in diameter, giving a total sensitive volume of 0.39

{mm}^{3}

. Further details on the probe and optical fiber design can be found in previous works . Photodetection was performed with an RCA‐4526 photomultiplier tube (PMT).…”

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

Madden

et al. 2019

Medical Physics

Self Cite

“…Thicknesses of 100 m and 50 m were used, defining sensitive volumes of 0.079 mm 3 and 0.039 mm 3 respectively. A 500 m probe was also fabricated using BC-444 scintillator (with a slower rise time than the BC-400) to test a method for temporal separation of Cherenkov light being developed [29].…”

Section: Photonic Dosimeter Designs and Testsmentioning

confidence: 99%

Recent advances in photonic dosimeters for medical radiation therapy

2018

Front. Optoelectron.

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Radiation therapy, which uses X-rays to destroy or injure cancer cells, has become one of the most important modalities to treat the primary cancer or advanced cancer. High resolution, water equivalent and passive X-ray dosimeters are highly desirable for developing quality assurance (QA) systems for novel cancer therapy like microbeam radiation therapy (MRT) which is currently under development. Here we present the latest developments of high spatial resolution scintillator based photonic dosimeters, and their applications to clinical external radiation beam therapies: specifically high energy linear accelerator (LINAC) photon beams and low energy synchrotron photon beams. We have developed optical fiber dosimeters with spatial resolutions ranging from 50 to 500 mm and tested them with LINAC beams and synchrotron microbeams. For LINAC beams, the fiberoptic probes were exposed to a 6 MV, 10 cm by 10 cm Xray field and, the beam profiles as well as the depth dose profiles were measured at a source-tosurface distance (SSD) of 100 cm. We have also demonstrated the possibility for temporally separating Cherenkov light from the pulsed LINAC scintillation signals. Using the 50 mm fiber probes, we have successfully resolved the microstructures of the microbeams generated by the imaging and medical beamline (IMBL) at the Australian Synchrotron and measured the peak-to-valley dose ratios (PVDRs). In this paper, we summarize the results we have achieved so far, and discuss the possible solutions to the issues and challenges we have faced, also highlight the future work to further enhance the performances of the photonic dosimeters.

“…Pulse gating methods such as temporal filtration remove 99% of the Cerenkov radiation response at the expense of a 44% loss in scintillation response. Temporal analytic methods do not experience the loss in scintillation siganl inherent to temporal filtration, however accuracy in Cerenkov radiation estimation has not yet been sufficient to result in clinically acceptable dose discrepancies in scintillator dose measurement [7,8,9,10].…”

Section: Introductionmentioning

confidence: 99%

Temporal separation of Cerenkov radiation and scintillation using artificial neural networks in Clinical LINACs

Madden

et al. 2018

Physica Medica

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The irradiation of scintillator-fiber optic dosimeters by clinical LINACs results in the measurement of scintillation and Cerenkov radiation. In scintillator-fiber optic dosimetry, the scintillation and Cerenkov radiation responses are separated to determine the dose deposited in the scintillator volume. Artificial neural networks (ANNs) were trained and applied in a novel single probe method for the temporal separation of scintillation and Cerenkov radiation. Six dose profiles were measured using the ANN, with the dose profiles compared to those measured using background subtraction and an ionisation chamber. The average dose discrepancy of the ANN measured dose was 2.2% with respect to the ionisation chamber dose and 1.2% with respect to the background subtraction measured dose, while the average dose discrepancy of the background subtraction dose was 1.6% with respect to the ionisation chamber dose. The ANNs performance was degraded when compared with background subtraction, arising from an inaccurate model used to synthesise ANN training data.