Characterization of the plastic scintillation detector Exradin W2 for small field dosimetry

Abstract

Purpose: Small field dosimetry has been an active area of research for over a decade. It is now known that large dosimetric errors can be introduced if proper detectors or correction factors are not used. The International Atomic Energy Agency (IAEA) through the technical report series No. 483 provides guidelines for small field dosimetry procedures as well as correction factors for most detectors available in the market. The plastic scintillator detector (PSD) Exradin W1 has been found to have a correction factor close to unity; however, it is not designed for beam scanning. To overcome this limitation, the new PSD Exradin W2 has been developed to be used as a scanning as well as a relative dosimeter. Characterization of this detector in small field dosimetry is presented in this study.

Methods: A 6 MV beam from a Varian-Edge linac was used to collect data for the characterization of a W2 detector. Cerenkov light ratio (CLR) is corrected through a separate new electrometer system that comes with the W2 detector. The parameters investigated include the dose and dose rate linearity, beam profiles, percent depth dose (PDD), field output factors, and temperature response. The results were compared with Gafchromic film (EBT-3 film) for beam profiles. The field output factor and temperature response were compared to the Exradin W1 detector.

Results: The dose linearity measured with 600 MU/min dose rate showed minimal variations (<0.5%) even for small MU, and similar results were seen for dose rate linearity. The comparison of field output factors between the W2 and W1 showed small differences for various depth and field sizes. The temperature response showed small variation when the temperature was varied from $6^{\circ }C$ to ${50}^{\circ }C$ . The slope was $-0.0017{/}^{\circ }C$ and $-0.0016{/}^{\circ }C$ for the W2 and the W1 detector, respectively. The differences in profiles are 0.5% in umbra and penumbra region for $1\times 1{\text{cm}}^2$ field size when compared to the EBT-3 film profile.

Conclusions: The W2 scintillator detector showed similar dosimetric and temperature properties to the W1 scintillator detector. The main advantage of the W2 detector among other plastic scintillators is the beam scanning capabilities that, combined with its correction factor of 1.0, make it an ideal detector for commissioning of SRS and SBRT techniques.

Keywords: Exradin W2; plastic scintillator detector; scintillator characterization; small field dose profiles; small field dosimetry; small field output factors.