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Dose rate constant of a Cesium‐131 interstitial brachytherapy seed measured by thermoluminescent dosimetry and gamma‐ray spectrometry
Author(s) -
Chen Z.,
Bongiorni P.,
Nath R.
Publication year - 2005
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.2098127
Subject(s) - kerma , thermoluminescent dosimeter , dosimetry , dosimeter , thermoluminescent dosimetry , thermoluminescence , brachytherapy , nuclear medicine , x ray , radiochemistry , gamma ray , imaging phantom , analytical chemistry (journal) , materials science , physics , chemistry , nuclear physics , luminescence , medicine , radiation therapy , chromatography , radiology , optoelectronics
The aim of this work was to conduct an independent determination of the dose rate constant of the newly introduced Model CS‐1 Cs131 seed. A total of eight Cs131 seeds were obtained from the seed manufacturer. The air‐kerma strength of each seed was measured by the manufacturer whose calibration is traceable to the air‐kerma strength standard established for the Cs131 seeds at the National Institute of Standards and Technology ( 1 σ uncertainty < 1 % ). The dose rate constant of each seed was measured by two independent methods: One based on the actual photon energy spectrum emitted by the seed using gamma‐ray spectrometry and the other based on the dose‐rate measured by thermoluminescent dosimeter (TLD) in a Solid Water™ phantom. The dose rate constant in water determined by the gamma‐ray spectrometry technique and by the TLD dosimetry are 1.066 ± 0.064cGyh − 1U − 1and 1.058 ± 0.106cGyh − 1U − 1, respectively, showing excellent agreement with each other. These values, however, are approximately 15% greater than a previously reported value of 0.915cGyh − 1U − 1[Med. Phys. 31, 1529–1538 (2004)]. Although low‐energy fluorescent x rays at 16.6 and 18.7 keV, originating from niobium present in the seed construction, were measured in the energy spectrum of the Cs131 seeds, their yields were not sufficient to lower the dose rate constant to the value of 0.915cGyh − 1U − 1. Additional determinations of the dose rate constant may be needed to establish an AAPM recommended consensus value for routine clinical use of the Cs131 seed.