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Spectra and air‐kerma strength for encapsulated 192 Ir sources
Author(s) -
Borg Jette,
Rogers David W. O.
Publication year - 1999
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 - 10.1118/1.598763
Subject(s) - kerma , physics , dosimetry , photon , bremsstrahlung , materials science , nuclear physics , optics , nuclear medicine , medicine
The photon spectra in vacuum around four types of192 Ir HDR brachytherapy sources are calculated using the Monte Carlo code EGS4 and the most recent spectral information on192 Ir decay. The air‐kerma strengths per unit activity are calculated based on the photon fluence around a bare192 Ir 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.