Spectra and air-kerma strength for encapsulated 192Ir sources

Abstract

The photon spectra in vacuum around four types of 192Ir HDR brachytherapy sources are calculated using the Monte Carlo code EGS4 and the most recent spectral information on 192Ir decay. The air-kerma strengths per unit activity are calculated based on the photon fluence around a bare 192Ir source and around each of four types of encapsulated sources using recent mass energy-absorption coefficients. For the full spectrum the bare vs encapsulated difference is up to 23% due to the large air-kerma contribution from the unfiltered low-energy photons. For the penetrating part of the photon spectrum (> 11.3 keV), the air-kerma strength per unit source activity on the transverse axis for a bare source is 2-15% higher than for the encapsulated sources due to the attenuation and absorption in the core and the encapsulating material. The contribution to the air-kerma strength from photons scattered in the capsule and from bremsstrahlung are calculated to increase the air-kerma strength by 2-4% and 0.2-0.3%, respectively. Air-kerma strengths for a variety of sources agree well with previously reported results for sources from Nucletron International, Best Industries, Inc., and Alpha-Omega Services, Inc. In addition we present air-kerma strengths for the present model of the HDR source from Nucletron International and the source from Varian Associates, Inc.

Dose errors due to inhomogeneities in balloon catheter brachytherapy for breast cancer

“…Comparison of calculated air kerma strengths per unit activity, S k /A with published data. The cutoff energies of photon fluence spectra in the parenthesis of the last two columns were 11.3 keV and 60 keV for Borg and Rogers (13), and 60 keV for Büermann et al (14). The values of Borg and Rogers were averaged at several distances from 2 to 50 cm Hereafter, all dose rates were normalized at the air kerma strength of 4.082 ϫ 10 4 U, which corresponds to an apparent activity of 10 Ci.…”

An EGSnrc investigation of the air-kerma strength, dose rate constant, and radial dose function of 125I brachytherapy sources

“…The photon fluence spectrum (at 5 keV intervals) at 100 cm along the transverse axis was scored in a 0.5-cm-thick and 0.5-mm-high cylindrical voxel positioned symmetrically about the source axis. As [20,21] in their study on the calculation of fluence spectra and air-kerma strength of 192 I sources, the fluence spectrum was subsequently converted to air-kerma per initial photon (Gy/initial photon) by use of the mass-energy-absorption coefficient of air [22]. The authors utilized the EGS4-based [23] FLURZ user-code in their study.…”

Comparison of air‐kerma strength determinations for HDR 192Ir sources

“…(7). Borg and Rogers 9 found that there is no significant difference between the spectra in-air and in-vacuum.…”