Commissioning an Exradin W2 plastic scintillation detector for clinical use in small radiation fields

Abstract

The purpose of this work is to evaluate the Standard Imaging Exradin W2 plastic scintillation detector (W2) for use in the types of fields used for stereotactic radiosurgery. Methods: Prior to testing the W2 in small fields, the W2 was evaluated in standard large field conditions to ensure good detector performance. These tests included energy dependence, short-term repeatability, dose-response linearity, angular dependence, temperature dependence, and dose rate dependence. Next, scan settings and calibration of the W2 were optimized to ensure high quality data acquisition. Profiles of small fields shaped by cones and multi-leaf collimator (MLCs) were measured using the W2 and IBA RAZOR diode in a scanning water tank. Output factors for cones (4-17.5 mm) and MLC fields (1, 2, 3 cm) were acquired with both detectors. Finally, the dose at isocenter for seven radiosurgery plans was measured with the W2 detector. Results: W2 exhibited acceptable warm-up behavior, short-term reproducibility, axial angular dependence, dose-rate linearity, and dose linearity. The detector exhibits a dependence upon energy, polar angle, and temperature. Scanning measurements taken with the W2 and RAZOR were in good agreement, with full-width half -maximum and penumbra widths agreeing to within 0.1 mm. The output factors measured by the W2 and RAZOR exhibited a maximum difference of 1.8%. For the seven point-dose measurements of radiosurgery plans, the W2 agreed well with our treatment planning system with a maximum deviation of 2.2%. The Čerenkov light ratio calibration method did not significantly impact the measurement of relative profiles, output factors, or point dose measurements. Conclusion:The W2 demonstrated dosimetric characteristics that are suitable for radiosurgery field measurements. The detector agreed well with the RAZOR diode for output factors and scanned profiles and showed good agreement with the treatment planning system in measurements of clinical treatment plans.

Characteristics of a plastic scintillation detector in photon beam dosimetry

“…The readings from this channel, Rc, are also expressed in nC. This technique was previously described by Beddar et al 17 For PSD W2 detector, Jacqmin et al 8 provided a practical approach to subtracting Cerenkov radiation. A pictorial of Cerenkov subtraction for BP-PSD is shown in Figure 2, indicating the position of sensor and Cerenkov Channel and the subtraction of the signal process.…”

“…Various techniques have been employed for correction which is needed for dosimetry. For example, Standard Imaging, W1 and W2 PSD use frequency discrimination (blue and green light) method as described by Guillot et al 18 and used in recent paper by Jacqmin et al 8 For BP-PSD signal subtraction method as described by the manufacturer is used 19 which is briefly described here. The amount of light produced by the PSD only is proportional to the dose deposited in the sensor.…”

“…21,22 ACR can be calculated as described by Underwood et al 23 Blue Physics describes this method, along with alternative methods, to calculate the ACR. 20 There are various other methods to compute the ACR as described by Jacqmin et al 8 The method used in this study is the cross-calibration method, which basically involves determining the ACR using the field output factor (FOF) of the 10×10 cm 2 (OF 10 ) and 3×3cm 2 field (OF 3 ).…”

“…Plastic scintillation detector (PSD) meets most of these characteristics and can represent a valuable tool for small-field dosimetry due to its small size, portability, energy independence,and tissue equivalence.When properly calibrated and used in conjunction with appropriate signal processing techniques, PSDs offer high-resolution dose measurements for a wide range of clinical applications, as shown by Beddar et al 1,2 The success of PSD led to the marketing of several PSD with unique niche that have been elaborated as a detector of choice as it does not have any perturbation and does not require correction factors in small fields. [3][4][5][6][7][8][9][10] There are several other PSDs that have inorganic or organic dopant devices showing similar high-resolution results without correction. 11,12 Most PSDs consist of a transparent plastic base, typically made of polystyrene, that is, doped with a scintillating material, such as fluor or anthracene.…”

“…When properly calibrated and used in conjunction with appropriate signal processing techniques, PSDs offer high‐resolution dose measurements for a wide range of clinical applications, as shown by Beddar et al 1,2 . The success of PSD led to the marketing of several PSD with unique niche that have been elaborated as a detector of choice as it does not have any perturbation and does not require correction factors in small fields 3–10 . There are several other PSDs that have inorganic or organic dopant devices showing similar high‐resolution results without correction 11,12 …”