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Title: TH-CD-201-09: High Spatial Resolution Absorbed Dose to Water Measurements Using Optical Calorimetry in Megavoltage External Beam Therapy

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 convertmore » 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.« less

Authors:
;  [1];  [2]
  1. School of Medicine and Public Health, University of Wisconsin-Madison, Madison, WI (United States)
  2. University of Wisconsin, Madison, WI (United States)
Publication Date:
OSTI Identifier:
22679278
Resource Type:
Journal Article
Resource Relation:
Journal Name: Medical Physics; Journal Volume: 43; Journal Issue: 6; Other Information: (c) 2016 American Association of Physicists in Medicine; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
60 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

Citation Formats

Flores-Martinez, E, DeWerd, L, and Radtke, J. TH-CD-201-09: High Spatial Resolution Absorbed Dose to Water Measurements Using Optical Calorimetry in Megavoltage External Beam Therapy. United States: N. p., 2016. Web. doi:10.1118/1.4958131.
Flores-Martinez, E, DeWerd, L, & Radtke, J. TH-CD-201-09: High Spatial Resolution Absorbed Dose to Water Measurements Using Optical Calorimetry in Megavoltage External Beam Therapy. United States. doi:10.1118/1.4958131.
Flores-Martinez, E, DeWerd, L, and Radtke, J. Wed . "TH-CD-201-09: High Spatial Resolution Absorbed Dose to Water Measurements Using Optical Calorimetry in Megavoltage External Beam Therapy". United States. doi:10.1118/1.4958131.
@article{osti_22679278,
title = {TH-CD-201-09: High Spatial Resolution Absorbed Dose to Water Measurements Using Optical Calorimetry in Megavoltage External Beam Therapy},
author = {Flores-Martinez, E and DeWerd, L and Radtke, J},
abstractNote = {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.},
doi = {10.1118/1.4958131},
journal = {Medical Physics},
number = 6,
volume = 43,
place = {United States},
year = {Wed Jun 15 00:00:00 EDT 2016},
month = {Wed Jun 15 00:00:00 EDT 2016}
}