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An Evaluation of Two Organic Liquid Scintillators for Use in Real-Time 3D Proton Dosimetry

S Ingram

W Scott Ingram1,2*, D Robertson1,2, S Beddar1,2, (1) The University of Texas MD Anderson Cancer Center, Houston, TX, (2) The University of Texas Graduate School of Biomedical Sciences, Houston, TX

SU-E-T-105 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: To evaluate the suitability of the organic liquid scintillators BC-531 and OptiPhase HiSafe 3 for real-time 3D proton dosimetry by measuring their scintillator-to-water stopping power ratios, density, and relative scintillation output.

Methods: Stopping power ratios were measured for BC-531 (not miscible with water) and OptiPhase at 0%, 25%, and 50% water concentrations. The ratios were derived from the water equivalent thickness of various scintillator volumes, which was quantified by the shift the scintillator introduces to the pristine Bragg peak of a 200 MeV proton beam. These depth-dose distributions were measured with the IBA Zebra detector.

Relative scintillation output was measured for a small volume of scintillator in the flat region of a 10 cm spread-out Bragg peak. Output was quantified for the OptiPhase solutions by integrating over an image taken with the Andor Technology Luca S electron-multiplying CCD camera.

Results: BC-531 showed the largest deviation from water in stopping power and density, with a scintillator-to-water stopping power ratio of 0.876 and density of 0.869 g/mL. For pure OptiPhase, that ratio was 0.990, and it increased to 0.997 and 0.996 for OptiPhase at 25% and 50% water concentrations. The density of the OptiPhase solutions was 0.963, 0.969, and 0.986 g/mL, respectively.

The scintillation output of OptiPhase at 25% and 50% water concentrations was 72% and 59% of that for the pure scintillator.

Conclusion: OptiPhase HiSafe 3 is a promising scintillator for real-time 3D dosimetry for proton therapy. Its ability to mix with water improves its water equivalence without an unacceptable loss of scintillation output. However, the stopping power of the pure scintillator (0% water) is already within 1% of that of water, so dilution is unnecessary to achieve water equivalence. The addition of water also causes the solution to become cloudy, which would limit the spatial accuracy of the dosimeter.

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