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A Novel Optical Calorimeter Applied to Proton Beam Dosimetry


J Meyer

A Cavan1, J Meyer2*, (1) University of Canterbury, Christchurch, New Zealand, (2) University of Washington Medical Center, Seattle, WA

TU-C-108-11 Tuesday 10:30AM - 12:30PM Room: 108

Purpose:
To demonstrate the proof-of-principle and feasibility of a novel optical calorimeter to determine radiation absorbed dose to water of a proton beam.

Methods:
The rise in temperature resulting from irradiation of a medium can be exploited by the use of a laser optics technique, named digital holographic interferometry (DHI). DHI can detect miniscule temperature changes in a transparent medium by measuring the corresponding change in the refractive index. A prototype of a lensless Fourier Transform digital holography (LFTDH) interferometer was developed and applied to the University of Washington experimental 30 MeV proton beam of 2 mm width. The output of the interferometer was digitally reconstructed and mathematically converted to absorbed dose through the calorimetric equations, resulting in a time series of high resolution two dimensional maps of absorbed dose.

Results:
The measurements qualitatively revealed the Bragg peak and relative dose profiles across the beam, in 2D dose maps with dimensions of ~6 x 8 mm (defined by the area of the optoelectronic sensor used). Heat diffusion within the water sample caused a blurring effect on the determined dose profiles but this can be accounted for by use of the heat equation. Experimental noise can further be reduced by improved isolation from the ambient conditions.

Conclusion:
A prototype DHI detector has been developed and shown to resolve small temperature changes resulting from irradiation of a water sample with a high dose rate proton beam. The results are high resolution (25 pixels/mm) and independent of beam type, energy and dose rate. These results present a proof-of-principle of DHI detectors and indicate the feasibility of the approach for high dose rate dosimetry applications.

Funding Support, Disclosures, and Conflict of Interest: Alicia Cavan acknowledges support from a Claude McCarthy fellowship (Universities New Zealand) for the proton beam research.

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