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Title: Determination of absorbed dose to water around a clinical HDR {sup 192}Ir source using LiF:Mg,Ti TLDs demonstrates an LET dependence of detector response

Abstract

Purpose: Experimental radiation dosimetry with thermoluminescent dosimeters (TLDs), calibrated in a {sup 60}Co or megavoltage (MV) photon beam, is recommended by AAPM TG-43U1for verification of Monte Carlo calculated absorbed doses around brachytherapy sources. However, it has been shown by Carlsson Tedgren et al.[Med. Phys. 38, 5539-5550 (2011)] that for TLDs of LiF:Mg,Ti, detector response was 4% higher in a {sup 137}Cs beam than in a {sup 60}Co one. The aim of this work was to investigate if similar over-response exists when measuring absorbed dose to water around {sup 192}Ir sources, using LiF:Mg,Ti dosimeters calibrated in a 6 MV photon beam. Methods: LiF dosimeters were calibrated to measure absorbed dose to water in a 6 MV photon beam and used to measure absorbed dose to water at distances of 3, 5, and 7 cm from a clinical high dose rate (HDR) {sup 192}Ir source in a polymethylmethacrylate (PMMA) phantom. Measured values were compared to values of absorbed dose to water calculated using a treatment planning system (TPS) including corrections for the difference in energy absorption properties between calibration quality and the quality in the users'{sup 192}Ir beam and for the use of a PMMA phantom instead of the water phantom underlyingmore » dose calculations in the TPS. Results: Measured absorbed doses to water around the {sup 192}Ir source were overestimated by 5% compared to those calculated by the TPS. Corresponding absorbed doses to water measured in a previous work with lithium formate electron paramagnetic resonance (EPR) dosimeters by Antonovic et al. [Med. Phys. 36, 2236-2247 (2009)], using the same irradiation setup and calibration procedure as in this work, were 2% lower than those calculated by the TPS. The results obtained in the measurements in this work and those obtained using the EPR lithium formate dosimeters were, within the expanded (k = 2) uncertainty, in agreement with the values derived by the TPS. The discrepancy between the results using LiF:Mg,Ti TLDs and the EPR lithium formate dosimeters was, however, statistically significant and in agreement with the difference in relative detector responses found for the two detector systems by Carlsson Tedgren et al. [Med. Phys. 38, 5539-5550 (2011)] and by Adolfsson et al.[Med. Phys. 37, 4946-4959 (2010)]. Conclusions: When calibrated in {sup 60}Co or MV photon beams, correction for the linear energy transfer (LET) dependence of LiF:Mg,Ti detector response will be needed as to measure absorbed doses to water in a {sup 192}Ir beam with highest accuracy. Such corrections will depend on the manufacturing process (MTS-N Poland or Harshaw TLD-100) and details of the annealing and read-out schemes used.« less

Authors:
; ; ; ;  [1];  [2];  [3];  [2]
  1. Radiation Physics, Department of Medical and Health Sciences (IMH), Faculty of Health Sciences, Linkoeping University, SE 581 85 Linkoeping (Sweden) and Swedish Radiation Safety Authority, SE 171 16 Stockholm (Sweden)
  2. (IMH), Faculty of Health Sciences, Linkoeping University, SE 581 85 Linkoeping (Sweden)
  3. (IMH), Faculty of Health Sciences, Linkoeping University, SE 581 85 Linkoeping (Sweden) and Department of Radiation Physics UHL, County Council of Oestergoetland, SE 581 85 Linkoeping (Sweden)
Publication Date:
OSTI Identifier:
22098747
Resource Type:
Journal Article
Resource Relation:
Journal Name: Medical Physics; Journal Volume: 39; Journal Issue: 2; Other Information: (c) 2012 American Association of Physicists in Medicine; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
62 RADIOLOGY AND NUCLEAR MEDICINE; BRACHYTHERAPY; CESIUM 137; COBALT 60; DOSE RATES; DOSIMETRY; ELECTRON SPIN RESONANCE; IRIDIUM 192; LET; LITHIUM FLUORIDES; MAGNESIUM ADDITIONS; PHANTOMS; PHOTON BEAMS; PLANNING; RADIATION DOSES; READOUT SYSTEMS; SEMICONDUCTOR DETECTORS; THERMOLUMINESCENT DOSEMETERS; TITANIUM ADDITIONS; WATER

Citation Formats

Carlsson Tedgren, Aasa, Elia, Rouba, Hedtjaern, Haakan, Olsson, Sara, Alm Carlsson, Gudrun, Radiation Physics, Department of Medical and Health Sciences, Radiation Physics, Department of Medical and Health Sciences, and Radiation Physics, Department of Medical and Health Sciences. Determination of absorbed dose to water around a clinical HDR {sup 192}Ir source using LiF:Mg,Ti TLDs demonstrates an LET dependence of detector response. United States: N. p., 2012. Web. doi:10.1118/1.3675401.
Carlsson Tedgren, Aasa, Elia, Rouba, Hedtjaern, Haakan, Olsson, Sara, Alm Carlsson, Gudrun, Radiation Physics, Department of Medical and Health Sciences, Radiation Physics, Department of Medical and Health Sciences, & Radiation Physics, Department of Medical and Health Sciences. Determination of absorbed dose to water around a clinical HDR {sup 192}Ir source using LiF:Mg,Ti TLDs demonstrates an LET dependence of detector response. United States. doi:10.1118/1.3675401.
Carlsson Tedgren, Aasa, Elia, Rouba, Hedtjaern, Haakan, Olsson, Sara, Alm Carlsson, Gudrun, Radiation Physics, Department of Medical and Health Sciences, Radiation Physics, Department of Medical and Health Sciences, and Radiation Physics, Department of Medical and Health Sciences. Wed . "Determination of absorbed dose to water around a clinical HDR {sup 192}Ir source using LiF:Mg,Ti TLDs demonstrates an LET dependence of detector response". United States. doi:10.1118/1.3675401.
@article{osti_22098747,
title = {Determination of absorbed dose to water around a clinical HDR {sup 192}Ir source using LiF:Mg,Ti TLDs demonstrates an LET dependence of detector response},
author = {Carlsson Tedgren, Aasa and Elia, Rouba and Hedtjaern, Haakan and Olsson, Sara and Alm Carlsson, Gudrun and Radiation Physics, Department of Medical and Health Sciences and Radiation Physics, Department of Medical and Health Sciences and Radiation Physics, Department of Medical and Health Sciences},
abstractNote = {Purpose: Experimental radiation dosimetry with thermoluminescent dosimeters (TLDs), calibrated in a {sup 60}Co or megavoltage (MV) photon beam, is recommended by AAPM TG-43U1for verification of Monte Carlo calculated absorbed doses around brachytherapy sources. However, it has been shown by Carlsson Tedgren et al.[Med. Phys. 38, 5539-5550 (2011)] that for TLDs of LiF:Mg,Ti, detector response was 4% higher in a {sup 137}Cs beam than in a {sup 60}Co one. The aim of this work was to investigate if similar over-response exists when measuring absorbed dose to water around {sup 192}Ir sources, using LiF:Mg,Ti dosimeters calibrated in a 6 MV photon beam. Methods: LiF dosimeters were calibrated to measure absorbed dose to water in a 6 MV photon beam and used to measure absorbed dose to water at distances of 3, 5, and 7 cm from a clinical high dose rate (HDR) {sup 192}Ir source in a polymethylmethacrylate (PMMA) phantom. Measured values were compared to values of absorbed dose to water calculated using a treatment planning system (TPS) including corrections for the difference in energy absorption properties between calibration quality and the quality in the users'{sup 192}Ir beam and for the use of a PMMA phantom instead of the water phantom underlying dose calculations in the TPS. Results: Measured absorbed doses to water around the {sup 192}Ir source were overestimated by 5% compared to those calculated by the TPS. Corresponding absorbed doses to water measured in a previous work with lithium formate electron paramagnetic resonance (EPR) dosimeters by Antonovic et al. [Med. Phys. 36, 2236-2247 (2009)], using the same irradiation setup and calibration procedure as in this work, were 2% lower than those calculated by the TPS. The results obtained in the measurements in this work and those obtained using the EPR lithium formate dosimeters were, within the expanded (k = 2) uncertainty, in agreement with the values derived by the TPS. The discrepancy between the results using LiF:Mg,Ti TLDs and the EPR lithium formate dosimeters was, however, statistically significant and in agreement with the difference in relative detector responses found for the two detector systems by Carlsson Tedgren et al. [Med. Phys. 38, 5539-5550 (2011)] and by Adolfsson et al.[Med. Phys. 37, 4946-4959 (2010)]. Conclusions: When calibrated in {sup 60}Co or MV photon beams, correction for the linear energy transfer (LET) dependence of LiF:Mg,Ti detector response will be needed as to measure absorbed doses to water in a {sup 192}Ir beam with highest accuracy. Such corrections will depend on the manufacturing process (MTS-N Poland or Harshaw TLD-100) and details of the annealing and read-out schemes used.},
doi = {10.1118/1.3675401},
journal = {Medical Physics},
number = 2,
volume = 39,
place = {United States},
year = {Wed Feb 15 00:00:00 EST 2012},
month = {Wed Feb 15 00:00:00 EST 2012}
}