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Comparison of W1 and W2 Plastic Scintillation Detectors with Small Field Output Factors

J McKay*, S Petro , M Axente , B Velasco , C Liu , Erlanger Health System, Chattanooga, TN


(Wednesday, 7/17/2019) 10:00 AM - 10:30 AM

Room: Exhibit Hall | Forum 4

Purpose: Plastic scintillation detectors (PSDs) have been highlighted in recent literature for their ability to accurately measure the output of small radiation field. Until recently, only one commercially available PSD (Exradin W1, Standard Imaging) was available. The updated W2 offers a smaller detector (1x1mm cylinder). A comparison between the W2, the W1, and the PTW 60017 diode was designed to validate the new W2 dosimetry system for clinical use.

Methods: Measurements were taken on a CyberKnife VSI with 6x FFF photons using fixed collimators. Each detector was placed at a depth of 1.5 cm in a 3D water tank. The detectors were centered by observing the highest reading across inline/crossline profiles determined by scanning the radiation field of a 5mm cone. 100 MUs were delivered for each reading. Output factors for the 5, 7.5, 10, 12.5, 15, 20, 30, and 60mm cones were calculated. A Cerenkov Light Ratio correction factor was measured and applied to all scintillator measurements.

Results: TRS-483 recommends a correction factor of 1.000 for the W1 PSD. It is assumed that the W2 has a unity correction factor as well. Recommended corrections were applied to the diode readings. Percent differences were calculated between each set of data, using the commissioning values as baseline (diode measurements). As expected, the diode showed an over response as compared with the scintillators (6.6%, 5mm cone), while the widest separation between the scintillators was 1.3% (5mm cone).

Conclusion: Agreement with the W1 while offering a smaller detector volume indicates potential for clinical utility as a small field detector. Further work will expand measurements to other beam data as well as patient verification. Recent publications have focused on the determination of output factors with new-generation detectors. This work expands that focus to the W2.


Scintillators, Small Fields, Dosimetry


Not Applicable / None Entered.

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