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Title: SU-G-201-08: Energy Response of Thermoluminescent Microcube Dosimeters in Water for Kilovoltage X-Ray Beams

Abstract

Purpose: To characterize the energy dependence for TLD-100 microcubes in water at kilovoltage energies. Methods: TLD-100 microcubes with dimensions of (1 × 1 × 1) mm{sup 3} were irradiated with kilovoltage x-rays in a custom-built thin-window liquid water phantom. The TLD-100 microcubes were held in Virtual Water™ probes and aligned at a 2 cm depth in water. Irradiations were performed using the M-series x-ray beams of energies ranging from 50-250 kVp and normalized to a {sup 60}Co beam located at the UWADCL. Simulations using the EGSnrc Monte Carlo Code System were performed to model the x-ray beams, the {sup 60}Co beam, the water phantom and the dosimeters in the phantom. The egs-chamber user code was used to tally the dose to the TLDs and the dose to water. The measurements and calculations were used to determine the intrinsic energy dependence, absorbed-dose energy dependence, and absorbed-dose sensitivity. These values were compared to TLD-100 chips with dimensions of (3.2 × 0.9 × 0.9) mm{sup 3}. Results: The measured TLD-100 microcube response per dose to water among all investigated x-ray energies had a maximum percent difference of 61% relative to {sup 60}Co. The simulated ratio of dose to water to the dose tomore » TLD had a maximum percent difference of 29% relative to {sup 60}Co. The ratio of dose to TLD to the TLD output had a maximum percent difference of 13% relative to {sup 60}Co. The maximum percent difference for the absorbed-dose sensitivity was 15% more than the used value of 1.41. Conclusion: These results confirm that differences in beam quality have a significant effect on TLD response when irradiated in water. These results also indicated a difference in TLD-100 response between microcube and chip geometries. The intrinsic energy dependence and the absorbed-dose energy dependence deviated up to 10% between TLD-100 microcubes and chips.« less

Authors:
; ; ;  [1]
  1. University of Wisconsin- Madison, Madison, WI (United States)
Publication Date:
OSTI Identifier:
22649250
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; BEAMS; COBALT 60; DOSEMETERS; ENERGY DEPENDENCE; IRRADIATION; MONTE CARLO METHOD; PHANTOMS; SIMULATION; WATER; X RADIATION

Citation Formats

Di Maso, L, Lawless, M, Culberson, W, and DeWerd, L. SU-G-201-08: Energy Response of Thermoluminescent Microcube Dosimeters in Water for Kilovoltage X-Ray Beams. United States: N. p., 2016. Web. doi:10.1118/1.4956881.
Di Maso, L, Lawless, M, Culberson, W, & DeWerd, L. SU-G-201-08: Energy Response of Thermoluminescent Microcube Dosimeters in Water for Kilovoltage X-Ray Beams. United States. doi:10.1118/1.4956881.
Di Maso, L, Lawless, M, Culberson, W, and DeWerd, L. 2016. "SU-G-201-08: Energy Response of Thermoluminescent Microcube Dosimeters in Water for Kilovoltage X-Ray Beams". United States. doi:10.1118/1.4956881.
@article{osti_22649250,
title = {SU-G-201-08: Energy Response of Thermoluminescent Microcube Dosimeters in Water for Kilovoltage X-Ray Beams},
author = {Di Maso, L and Lawless, M and Culberson, W and DeWerd, L},
abstractNote = {Purpose: To characterize the energy dependence for TLD-100 microcubes in water at kilovoltage energies. Methods: TLD-100 microcubes with dimensions of (1 × 1 × 1) mm{sup 3} were irradiated with kilovoltage x-rays in a custom-built thin-window liquid water phantom. The TLD-100 microcubes were held in Virtual Water™ probes and aligned at a 2 cm depth in water. Irradiations were performed using the M-series x-ray beams of energies ranging from 50-250 kVp and normalized to a {sup 60}Co beam located at the UWADCL. Simulations using the EGSnrc Monte Carlo Code System were performed to model the x-ray beams, the {sup 60}Co beam, the water phantom and the dosimeters in the phantom. The egs-chamber user code was used to tally the dose to the TLDs and the dose to water. The measurements and calculations were used to determine the intrinsic energy dependence, absorbed-dose energy dependence, and absorbed-dose sensitivity. These values were compared to TLD-100 chips with dimensions of (3.2 × 0.9 × 0.9) mm{sup 3}. Results: The measured TLD-100 microcube response per dose to water among all investigated x-ray energies had a maximum percent difference of 61% relative to {sup 60}Co. The simulated ratio of dose to water to the dose to TLD had a maximum percent difference of 29% relative to {sup 60}Co. The ratio of dose to TLD to the TLD output had a maximum percent difference of 13% relative to {sup 60}Co. The maximum percent difference for the absorbed-dose sensitivity was 15% more than the used value of 1.41. Conclusion: These results confirm that differences in beam quality have a significant effect on TLD response when irradiated in water. These results also indicated a difference in TLD-100 response between microcube and chip geometries. The intrinsic energy dependence and the absorbed-dose energy dependence deviated up to 10% between TLD-100 microcubes and chips.},
doi = {10.1118/1.4956881},
journal = {Medical Physics},
number = 6,
volume = 43,
place = {United States},
year = 2016,
month = 6
}
  • Purpose: To assess the effects of changes in beam quality on detector response in the kilovoltage energy range by modulating the x-ray tube voltage and the measurement depth in water. Methods: Measurements were performed with TLD-100 and TLD-100H thermoluminescent dosimeters and an A12 farmer-type ionization chamber. To assess the energy response of the detectors, irradiations were performed at a depth of 3 cm in a custom-built thin-window water phantom using the moderately filtered x-ray beams at the UWADCL (20 kVp-250 kVp) and a Co-60 beam.The x-ray beams and detectors were modeled using the EGSnrc Monte Carlo code. The model wasmore » validated by simulating dose to the collecting volume of an A12 farmer chamber and comparing it with measured A12 signal as a function of depth. Dose was tallied to each detector and to water for comparison with measurements. Simulations were used to calculate the predicted energy response, which was compared to the measured response of each detector. Dose to each detector and dose to water as a function of depth were also simulated. Results: Detector output per dose to water was found to deviate by up to 15%, 20% and 30% as a function of energy relative to Co-60 for the A12, TLD-100H and TLD-100, respectively. The EGSnrc simulations produced results similar to the measurements for ionization chambers, but discrepancies of up to 30% were observed for TLD-100H. Simulated detector response as a function of depth was found to vary by up to 3%. Conclusion: These results suggest that changes in beam quality in kilovoltage x-ray beams can have a significant impact on detector response. In-water detector response was found to differ from the previously investigated in-air response. Deviations in detector response as a function of depth were less significant, but could potentially cause dosimetric errors if ignored.« less
  • Optically stimulated luminescent detectors, which are widely used in radiation protection, offer a number of potential advantages for application in radiation therapy dosimetry. Their introduction into this field has been somewhat hampered by the lack of information on their radiation response in megavoltage beams. Here the response of a commercially available optically stimulated luminescent detector (OSLD) is determined as a function of energy, absorbed dose to water, and linear energy transfer (LET). The detector response was measured as a function of energy for absorbed doses from 0.5 to 4.0 Gy over the following ranges: 125 kVp to18 MV for photons,more » 6-20 MeV for electrons, 50-250 MeV for protons, and 290 MeV/u for the carbon ions. For the low LET beams, the response of the detector was linear up to 2 Gy with supralinearity occurring at higher absorbed doses. For the kilovoltage photons, the detector response relative to 6 MV increased with decreasing energy due to the higher atomic number of aluminum oxide (11.2) relative to water (7.4). For the megavoltage photons and electrons, the response was independent of energy. The response for protons was also independent of energy, but it was about 6% higher than its response to 6 MV photons. For the carbon ions, the dose response was linear for a given LET from 0.5 to 4.0 Gy, and no supralinearity was observed. However, it did exhibit LET dependence on the response relative to 6 MV photons decreasing from 1.02 at 1.3 keV/{mu}m to 0.41 at 78 keV/{mu}m. These results provide additional information on the dosimetric properties for this particular OSL detector and also demonstrate the potential for their use in photon, electron, and proton radiotherapy dosimetry with a more limited use in high LET radiotherapy dosimetry.« less