Characterization of a water‐equivalent fiber‐optic coupled dosimeter for use in diagnostic radiology

Abstract

This work reports on the characterization of a new fiber-optic coupled (FOC) dosimeter for use in the diagnostic radiology energy range. The FOC dosimeter was constructed by coupling a small cylindrical plastic scintillator, 500 microm in diameter and 2 mm in length, to a 2 m long optical fiber, which acts as a light guide to transmit scintillation photons from the sensitive element to a photo-multiplier tube (PMT). A serial port interface on the PMT permits real-time monitoring of light output from the dosimeter via a custom computer program. The FOC dosimeter offered excellent sensitivity and reproducibility, allowing doses as low as 0.16 mGy to be measured with a coefficient of variation of only 3.64%. Dose linearity was also excellent with a correlation coefficient of 1.000 over exposures ranging from 0.16 to 57.29 mGy. The FOC dosimeter exhibited little angular dependence from axial irradiation, varying by less than 5% over an entire revolution. A positive energy dependence was observed and measurements performed within a scatter medium yielded a 10% variation in sensitivity as beam quality changed due to hardening and scatter across a 16 cm depth range. The current dosimetry system features an array of five PMTs to allow multiple FOC dosimeters to be monitored simultaneously. Overall, the system allows for rapid and accurate dose measurements relevant to a range of diagnostic imaging applications.

Validating plastic scintillation detectors for photon dosimetry in the radiologic energy range

“…Some studies [10][11][12] have shown that the dose linearity, reproducibility, and angle independence of PSD are maintained in the diagnostic energy range, but these studies also found a positive variation in the energy response over the energy range of interest. Hyer et al 10 reported an increase of 10% in the PSD response at 15-cm depth owing to beam hardening and scattered radiation with a 120-kVp beam.…”

Characterization of a scintillating fibre detector for small animal imaging and irradiation dosimetry

“…The different prototypes described in literature present dosemeters with linear, reproducible dose measurements. [13][14][15] However, other studies also found an energy dependence of the dosemeter response, expressed as a decrease of sensitivity with decreasing energy. [16][17][18][19] In addition, in the kilovoltage energy range, the stem effect is mainly due to the fluorescence of the optical fibre and its contribution has been reported to be small.…”

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

“…The space surrounding the detector and that between the source and the detector are modeled as if filled with air. The calculation results are compared to free-in-air measurements of Hyer et al, 9 which were obtained with a CT unit operating at 120 kVp. Figure 4 shows the energy dependence of the PVT scintillator with a polystyrene protective layer but no optical fiber attached.…”

“…In this work, therefore, we investigated only azimuthal angular dependence. Only a few studies have been published on the angular dependence of PSD responses and they considered only low-energy photon beams, a diagnostic x-ray source, 9 and a brachytherapy source. 5,10 For the diagnostic x-ray source, the measurement was performed free-in-air for one revolution of a clinical computed tomography ͑CT͒ unit ͑op-erating at 120 kVp͒ around the detector.…”

“…The signal was reduced dramatically when the radiation was incident from the back of the PSD because of the attenuation of the x ray in the optical fiber. 9 It is expected that the effect would be reduced for in-phantom measurements due to scattering effect. For the brachytherapy sources, the measurement was performed in a polymethylmethacrylate ͑PMMA͒ phantom with an 192 Ir high dose-rate brachytherapy source.…”