Characterization of the Plastic Scintillator Detector System Exradin W2 in a High Dose Rate Flattening-Filter-Free Photon Beam

Abstract

(1) Background: The Exradin W2 is a commercially available scintillator detector designed for reference and relative dosimetry in small fields. In this work, we investigated the performance of the W2 scintillator in a 10 MV flattening-filter-free photon beam and compared it to the performance of ion chambers designed for small field measurements. (2) Methods: We measured beam profiles and percent depth dose curves with each detector and investigated the linearity of each system based on dose per pulse (DPP) and pulse repetition frequency. (3) Results: We found excellent agreement between the W2 scintillator and the ion chambers for beam profiles and percent depth dose curves. Our results also showed that the two-voltage method of calculating the ion recombination correction factor was sufficient to correct for the ion recombination effect of ion chambers, even at the highest DPP. (4) Conclusions: These findings show that the W2 scintillator shows excellent agreement with ion chambers in high DPP conditions.

Keywords: Exradin W2; dosimetry; flattening-filter-free; high dose per pulse; high dose rate; output constancy; plastic scintillator.

Figure 1

Exadrin W2 Scintillator from Standard Imaging (left) and the IBA Dosimetry CC01 (center) and CC08 (right) ion chambers.

Figure 2

Percent depth dose (PDD) curves measured with the Exradin W2 scintillator (blue) and the CC01 ion chamber (gray) using a 10 MV flattening-filter-free (FFF) beam at 100 cm source-to-surface distance for various field sizes. The difference between the two measurements (W2—CC01, orange) was less than 5% at all points and less than 1% at depths greater than d_max.

Figure 3

In-plane profiles measured with the Exradin W2 scintillator (blue) and the CC01 ion chamber (gray) using a 10 MV FFF beam at 100 cm source-to-surface distance for various field sizes. The difference between the two measurements (W2–CC01, orange) was less than 5% at all points and less than 1% at depths outside of the penumbra region.

Figure 4

(a) Output of the CC08 ion chamber (squares) and W2 scintillator (X) is constant as a function of nominal dose rate at 100 cm SSD (blue, top row), 90 cm SSD (orange, middle row), and 80 cm SSD (gray, bottom row). Each detector’s output was normalized to the reading from the respective detector and SSD at 800 MU/min. (b) Detector signal as a function of DPP for the W2 scintillator, and CC08 and CC01 ion chambers, relative to the signal at 100 SSD (0.14 cGy/MU). The theoretical relationship that was expected is shown with circles.