Abstract
Scintillation detectors are considered highly suitable for dosimetric measurement of small fields in radiotherapy due to their near-tissue equivalence and their small size. A commercially available scintillation detector, the Exradin W1 (Standard Imaging, Middleton, USA), has been previously characterised by two independent studies (Beierholm et al., 2014; Carrasco et al., 2015a, 2015b) but the results from these publications differed in some aspects (e.g. energy dependence, long term stability). The respective authors highlighted the need for more studies to be published (Beierholm et al., 2015; Carrasco et al., 2015a, 2015b).In this work, the Exradin W1 was characterised in terms of dose response, dependence on dose rate, energy, temperature and angle of irradiation, and long-term stability. The observed dose linearity, short-term repeatability and temperature dependence were in good agreement with previously published data. Appropriate corrections should therefore be applied, where possible, in order to achieve measurements with low-uncertainty. The angular dependence was characterised along both the symmetrical and polar axis of the detector for the first time in this work and a dose variation of up to 1% was observed. The response of the detector was observed to decrease at a rate of approximately 1.6%kGy−1 for the first 5kGy delivered, and then stabilised to 0.2%kGy−1 in the subsequent 20kGy.The main goal of this work was to assess the suitability of the Exradin W1 for use in dose verification measurements for stereotactic radiosurgery. The results obtained confirm that the detector is suitable for use in such situations. The detector is now utilised in a multi-centre stereotactic radiosurgery dosimetric audit, with the application of appropriate correction factors.
Highlights
Plastic scintillation detectors (PSD) have been investigated for their performance in medical radiation dosimetry for more than two decades (Beaulieu et al, 2013)
There were no significant differences between triggered and manual collections for doses above 1 Gy, where variations of up to ± 0.1% were observed
The results demonstrated that using manual mode and the consistent collection method described, accurate measurements are acquired in the dose range of interest, making this method suitable for the proposed dosimetry audit
Summary
Plastic scintillation detectors (PSD) have been investigated for their performance in medical radiation dosimetry for more than two decades (Beaulieu et al, 2013) They are considered suitable for radiotherapy applications, as they can be manufactured in small sizes, have tissue equivalent density and are capable of performing real-time measurements. Measurements with the PSD in two setup orientations, of maximum and minimum optical fibre in the radiation field, are used for the determination of the Cherenkov Light Ratio (CLR) correction. This is necessary to remove the stem signal produced by irradiation of the fibre. The manufacturer provides a 30×30 cm polystyrene calibration slab that allows placement of the detector fibre in the minimum and maximum fibre orientations (Fig. 1)
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