Attenuation of intracavitary applicators in 192Ir-HDR brachytherapy

Unlike the penetrating monoenergetic 662 keV gamma rays emitted by 137Cs LDR sources, the spectrum of 192Ir used in HDR brachytherapy contains low-energy components. Since these are selectively absorbed by the high-atomic number materials of which intracavitary applicators are made, the traditional...

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Bibliographic Details
Published inMedical physics (Lancaster) Vol. 31; no. 7; p. 2097
Main Authors Ye, Sung-Joon, Brezovich, Ivan A, Shen, Sui, Duan, Jun, Popple, Richard A, Pareek, Prem N
Format Journal Article
LanguageEnglish
Published United States 01.07.2004
Subjects
Algorithms
Brachytherapy - instrumentation
Brachytherapy - methods
Computer Simulation
Equipment Failure Analysis - methods
Female
Genital Neoplasms, Female - radiotherapy
Humans
Iridium Radioisotopes - analysis
Iridium Radioisotopes - therapeutic use
Models, Biological
Monte Carlo Method
Radiometry - methods
Radiotherapy Dosage
Radiotherapy Planning, Computer-Assisted - methods
Reproducibility of Results
Scattering, Radiation
Sensitivity and Specificity
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Summary:Unlike the penetrating monoenergetic 662 keV gamma rays emitted by 137Cs LDR sources, the spectrum of 192Ir used in HDR brachytherapy contains low-energy components. Since these are selectively absorbed by the high-atomic number materials of which intracavitary applicators are made, the traditional neglect of applicator attenuation can lead to appreciable dose errors. We investigated the attenuation effects of a uterine applicator, and of a set of commonly used vaginal cylinders. The uterine applicator consists of a stainless steel source guide tube with a wall thickness of 0.5 mm and a density of 8.02 g/cm3, whereas the vaginal cylinders consist of the same stainless steel tube plus concentric polysulfone cylinders with a radius of 1 or 2 cm and a density of 1.40 g/cm3. Monte Carlo simulations were performed to compute dose distributions for a bare 192Ir-HDR source, and for the same source located within the applicators. Relative measurements of applicator attenuation using ion-chambers (0.125 cm3) confirmed the Monte Carlo results within 0.5%. We found that the neglect of the applicator attenuation overestimates the dose along the transverse plane by up to 3.5%. At oblique angles, the longer photon path within applicators worsens the error. We defined attenuation-corrected radial dose and anisotropy functions, and applied them to a treatment having multiple dwell positions inside a vaginal cylinder.
ISSN:0094-2405
DOI:10.1118/1.1762791