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Impact of source‐production revision on the dose‐rate constant of C 131 s interstitial brachytherapy sources
Author(s) -
Chen Zhe Jay,
Bongiorni Paul,
Nath Ravinder
Publication year - 2010
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 - 10.1118/1.3453766
Subject(s) - photon , radioactive source , brachytherapy , physics , photon energy , nuclear medicine , radiochemistry , analytical chemistry (journal) , atomic physics , chemistry , detector , optics , radiation therapy , medicine , radiology , chromatography
Purpose Since its introduction in 2004, the model CS‐1 Rev.1C131 s source has been used in many radiation therapy clinics for prostate brachytherapy. In 2006, this source model underwent a Rev.2 production revision. The aim of this work was to investigate the dosimetric influences of the Rev.2 production revision using high‐resolution photon spectrometry. Methods Three CS‐1 Rev.1 and three CS‐1 Rev.2C131 s sources were used in this study. The relative photon energy spectrum emitted by each source in the transverse bisector of the source was measured using a high‐resolution germanium detector designed for low‐energy photon spectrometry. Based on the measured photon energy spectrum and the radioactivity distribution in the source, the dose‐rate constant( Λ )of each source was determined. The effects of the Rev.2 production revision were quantified by comparing the emitted photon energy spectra and the Λ values determined for the sources manufactured before and after the production revision. Results The relative photon energy spectrum originating from the principal emissions ofC131 s was found to be nearly identical before and after the Rev.2 revision. However, the portion of the spectrum originating from the production of fluorescent x rays in niobium, a trace element present in the source construction materials, was found to differ significantly between the Rev.1 and Rev.2 sources. The peak intensity of the NbK αand NbK βfluorescent x rays from the Rev.2 source was approximately 35% of that from the Rev.1 source. Consequently, the nominal Λ value of the Rev.2 source was found to be greater than that determined for the Rev.1 source by approximately 0.7 % ± 0.5 % . Conclusions A significant reduction (65%) in relative niobium fluorescent x‐ray yield was observed in the Rev.2C131 s sources. The impact of this reduction on the dose‐rate constant was found to be small, with a relative difference of less than 1%. This study demonstrates that photon spectrometry can be used as a sensitive and convenient tool for monitoring and for quantifying the dosimetric effects of brachytherapy source‐production revisions. Because production revision can change both the geometry and the atomic composition of brachytherapy sources, its dosimetric impact should be carefully monitored and evaluated for each production revision.