Monte Carlo study of the energy and angular dependence of the response of plastic scintillation detectors in photon beams

Abstract

Purpose: By using Monte Carlo simulations, the authors investigated the energy and angular dependence of the response of plastic scintillation detectors ͑PSDs͒ in photon beams. Methods: Three PSDs were modeled in this study: A plastic scintillator ͑BC-400͒ and a scintillating fiber ͑BCF-12͒, both attached by a plastic-core optical fiber stem, and a plastic scintillator ͑BC-400͒ attached by an air-core optical fiber stem with a silica tube coated with silver. The authors then calculated, with low statistical uncertainty, the energy and angular dependences of the PSDs' responses in a water phantom. For energy dependence, the response of the detectors is calculated as the detector dose per unit water dose. The perturbation caused by the optical fiber stem connected to the PSD to guide the optical light to a photodetector was studied in simulations using different optical fiber materials. Results: For the energy dependence of the PSDs in photon beams, the PSDs with plastic-core fiber have excellent energy independence within about 0.5% at photon energies ranging from 300 keV ͑monoenergetic͒ to 18 MV ͑linac beam͒. The PSD with an air-core optical fiber with a silica tube also has good energy independence within 1% in the same photon energy range. For the angular dependence, the relative response of all the three modeled PSDs is within 2% for all the angles in a 6 MV photon beam. This is also true in a 300 keV monoenergetic photon beam for PSDs with plastic-core fiber. For the PSD with an air-core fiber with a silica tube in the 300 keV beam, the relative response varies within 1% for most of the angles, except in the case when the fiber stem is pointing right to the radiation source in which case the PSD may over-response by more than 10%. Conclusions: At Ϯ1% level, no beam energy correction is necessary for the response of all three PSDs modeled in this study in the photon energy ranges from 200 keV ͑monoenergetic͒ to 18 MV ͑linac beam͒. The PSD would be even closer to water equivalent if there is a silica tube around the sensitive volume. The angular dependence of the response of the three PSDs in a 6 MV photon beam is not of concern at 2% level.

Study of the response of plastic scintillation detectors in small‐field 6 MV photon beams by Monte Carlo simulations

“…These values are higher than those obtained for the same radiation source and at the same depth in the water phantom with a large ͑10ϫ 10 cm 2 ͒ field size. 18 This is mainly because the field size here is so small and comparable to the size of the PSD's sensitive region. Figure 3 also shows the angular dependence of two bare polystyrene PSDs, which correspond to the size of the sensitive regions of the BCF-12 and BC-400 PSDs.…”

“…The detailed data and/or schematic drawings for these PSDs can be found in our previous study. 18 A CC01 compact chamber ͑IBA Dosimetry GmbH, Schwarzenbruck, Germany͒ is also simulated here for comparison. The detec-tors ͑PSDs or chamber͒ were simulated as if they were positioned at a depth of 10 cm in a cubic water phantom.…”

Dosimetric characterization of the Exradin W1 plastic scintillator detector through comparison with an in-house developed scintillator system

“…Monte Carlo studies have shown that the use of PSDs is essentially perturbation-free in radiotherapy photon beams (Beddar et al, 2005;Wang et al, 2010). Likewise, the absorbed dose ratio between a detector voxel and a water voxel of the same size has been found to be independent of irradiation settings such as energy, field size and irradiation depth.…”

Technical Note: Evaluation of plastic scintillator detector for small field stereotactic patient‐specific quality assurance

“…There are many publications on the dosimetric characteristics of the PSD . Among which, several studies demonstrated that the PSD achieved similar dose response to other widely accepted benchmarks, such as Monte Carlo, Gafchromic films and diamond detectors .…”