Attenuation of intracavitary applicators in192Ir-HDR brachytherapy

Academic Article

Abstract

  • Unlike the penetrating monoenergetic 662 keV gamma rays emitted by137Cs LDR sources, the spectrum of192Ir 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 bare192Ir-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. © 2004 American Association of Physicists in Medicine.
  • Digital Object Identifier (doi)

    Author List

  • Ye SJ; Brezovich IA; Shen S; Duan J; Popple RA; Pareek PN
  • Start Page

  • 2097
  • End Page

  • 2106
  • Volume

  • 31
  • Issue

  • 7