To characterize the low energy behavior of scintillating materials used in plastic scintillation detectors (PSDs), 3 PSDs were developed using polystyrene-based scintillating materials emitting in different wavelengths. These detectors were exposed to National Institute of Standards and Technology (NIST)-matched low-energy beams ranging from 20 kVp to 250 kVp, and to (137)Cs and (60)Co beams. The dose in polystyrene was compared to the dose in air measured by NIST-calibrated ionization chambers at the same location. Analysis of every beam quality spectrum was used to extract the beam parameters and the effective mass energy-absorption coefficient. Monte Carlo simulations were also performed to calculate the energy absorbed in the scintillators' volume. The scintillators' expected response was then compared to the experimental measurements and an energy-dependent correction factor was identified to account for low-energy quenching in the scintillators. The empirical Birks model was then compared to these values to verify its validity for low-energy electrons. The clear optical fiber response was below 0.2% of the scintillator's light for x-ray beams, indicating that a negligible amount of fluorescence contamination was produced. However, for higher-energy beams ((137)Cs and (60)Co), the scintillators' response was corrected for the Cerenkov stem effect. The scintillators' response increased by a factor of approximately 4 from a 20 kVp to a (60)Co beam. The decrease in sensitivity from ionization quenching reached a local minimum of about [Formula: see text] between 40 keV and 60 keV x-ray beam mean energy, but dropped by 20% for very low-energy (13 keV) beams. The Birks model may be used to fit the experimental data, but it must take into account the energy dependence of the kB quenching parameter. A detailed comprehension of intrinsic scintillator response is essential for proper calibration of PSD dosimeters for radiology.
For dose rates higher than 3 mGy/s, the PIN diode is the most effective photodetector in terms of performance/cost ratio. For lower dose rates, such as those seen in interventional radiology or high-gradient radiotherapy, PMTs are the optimal choice.
In this work, the authors applied an Air-Kerma in air based radiochromic film reference dosimetry protocol for in vivo skin dose measurements. In this work, they employed green channel extracted from the scanned RGB image for dose measurements in the range from 0 to 200 mGy. Measured skin doses and corresponding DLPs were higher than DLPs provided by the CT scanner manufacturer as they were measured on patients' skin.
Purpose: To monitor and measure, in real‐time, patient skin dose during fluoroscopically‐guided interventional (FGI) procedures using a novel plastic scintillation dosimeter (PSD). Methods: A clear optical fiber of 1 mm diameter, 10 m long, is optically coupled to a plastic scintillation fiber (BCF‐60) of 1 mm diameter, 10 mm long. On its other end, the clear fiber is connected to an avalanche photodiode, APD (C4777‐01, Hamamatsu). An electrometer collects the APD charge and displays live graph and dose values. Initial calibration is achieved with a NRC calibrated Farmer‐type ionization chamber (Exradin A12, Standard Imaging). The PSD and the chamber are set on an Allura Xper Fd10/10 (Philips) intervention table at the Air Kerma reference point, 150 mm below isocentre. In compliance with TG‐125 data collection methodology, slabs of solid water are gradually added over the instruments. In order to preserve image quality, the automatic controls increase tube current and kVp accordingly. Acquisitions are made in both cine‐fluorography and fluoroscopy operation modes, at 15 frames/s. Measurements were repeated by replacing the solid water by an Alderson RANDO phantom, with image intensifier as close as possible of the surface to replicate clinical protocols. Results: The calibration curves indicate that PSD response is linear below 80 kVp, but exhibits a quadratic behavior above, with a rate of 20–40 pA/mGy over Air Kerma Rate range of 0.10–16 mGy/s. The PSD can read dose rate as low as 1.7 mGy/s ± 5 %. However, uncertainties rise above 10 % for dose rate less than 1 mGy/s. Phantom measurements indicate that the dosimeter is accurate for clinical applications. Conclusion: A PSD has been calibrated and tested in order to monitor and measure low dose rates involved in FGI procedures in real‐time. The next steps will include Monte Carlo calculations to assess accuracy before starting clinical procedures.
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