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Development of a Liquid Scintillation Detector for External Beam Dosimetry

D Sinn

D Sinn*, M Mackenzie, Cross Cancer Institute, Edmonton, Alberta

SU-E-T-168 Sunday 3:00:00 PM - 6:00:00 PM Room: Exhibit Hall

The goal of this research was to design a liquid scintillation dosimeter that could be used for
relative dosimetry of linear accelerator fields. The project emphasized minimization of cost and ease of use.

The scintillator that was used in this research was BETAMAX-ES scintillation cocktail from MP
Biomedical. This particular scintillator was selected due to its relatively high scintillation yield and low
cost. The entirety of the scintillator used the measurements was supplied free of cost. The housing for the liquid was constructed from PVC and is cylindrical with one tapered end. One fiber of the dual optical fibers transmits the generated photons to the CCD while the other fiber is used for Cerenkov

The detector used comes from a Philips SPC880NC webcam. The plastic casing of the webcam
was removed so that only the printed circuit board, USB cable and lens eyepiece holder remained. The
sensor employed is the Sony ICX098QB CCD, which is 3.2mm by 2.4mm and each pixel is 5.6µm by
5.6µm. A small cylindrical insert was manufactured that was inserted into the lens eyepiece holder to get adequate mechanical coupling of the fibers to the CCD face.

Images were acquired with a freeware image acquisition tool, SharpCap, and analyzed with the
Matlab commercial math package from Mathworks.

Measurements have been performed that show that the detector is able to accurately measure
tissue maximum ratio and the relative dose factor. The detector was able to accurately measure
physical wedge factors and made good predictions of the modulation factor for a patient's 7-field IMRT plan.

This work has shown that relative dosimetry can be performed using an inexpensive liquid
scintillation detector. This could be expanded to include an array of liquid scintillator cells for
measurement of beam profiles and other more complex problems.

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