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Author Flores-Martinez, E. ♦ DeWerd, L. ♦ Radtke, J.
Source United States Department of Energy Office of Scientific and Technical Information
Content type Text
Language English
Subject Keyword APPLIED LIFE SCIENCES ♦ ABSORBED RADIATION DOSES ♦ CALORIMETRY ♦ IMAGES ♦ IRRADIATION ♦ LINEAR ACCELERATORS ♦ MEV RANGE 01-10 ♦ PHANTOMS ♦ PROTON BEAMS ♦ RADIATION DOSE DISTRIBUTIONS ♦ REFRACTIVE INDEX ♦ SPATIAL RESOLUTION ♦ TEMPERATURE DEPENDENCE ♦ TIME DEPENDENCE ♦ VISIBLE RADIATION ♦ WATER
Abstract Purpose: To develop and implement a high spatial resolution calorimeter methodology to measure absorbed dose to water (ADW) using phase shifts (PSs) of light passing through a water phantom and to compare measurements with theoretical calculations. Methods: Radiation-induced temperature changes were measured using the PSs of a He-Ne laser beam passing through a (10×10×10) cm{sup 3} water phantom. PSs were measured using a Michelson interferometer and recording the time-dependent fringe patterns on a CCD camera. The phantom was positioned at the center of the radiation field. A Varian 21EX was used to deliver 500 MU from a 9 MeV beam using a (6×6) cm{sup 2} cone. A 127cm SSD was used and the PSs were measured at depths ranging from of 1.90cm to 2.10cm in steps of 0.05cm by taking profiles at the corresponding rows across the image. PSs were computed by taking the difference between pre- and post-irradiation image frames and then measuring the amplitude of the resulting image profiles. An amplitude-to-PS calibration curve was generated using a piezoelectric transducer to mechanically induce PSs between 0.05 and 1.50 radians in steps of 0.05 radians. The temperature dependence of the refractive index of water at 632.8nm was used to convert PSs to ADW. Measured results were compared with ADW values calculated using the linac output calibration and commissioning data. Results: Milli-radian resolution in PS measurement was achieved using the described methodology. Measured radiation-induced PSs ranged from 0.10 ± 0.01 to 0.12 ± 0.01 radians at the investigated depths. After converting PSs to ADW, measured and calculated ADW values agreed within the measurement uncertainty. Conclusion: This work shows that interferometer-based calorimetry measurements are capable of achieving sub-millimeter resolution measuring 2D temperature/dose distributions, which are particularly useful for characterizing beams from modalities such as SRS, proton therapy, or microbeams.
ISSN 00942405
Educational Use Research
Learning Resource Type Article
Publisher Date 2016-06-15
Publisher Place United States
Journal Medical Physics
Volume Number 43
Issue Number 6


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