Dosimetric characteristics and a standard for the 198Au seed used in interstitial brachytherapy

Abstract

The American Association of Physicists in Medicine (AAPM) Task Group 43 report (TG-43) provides a dosimetry protocol for brachytherapy dose calculations, and results for some sources. Gold 198 seeds days, have been used for brachytherapy treatments including brain, eye, and prostate tumors. However, the National Institute of Standards and Technology (NIST) does not have a standard for seeds as for and seeds, and the TG-43 report gives no data for For these reasons and with the conversion of treatment planning systems to TG-43 based methods, both Monte Carlo calculations (MCNP 4C) and thermoluminescent dosimeters (TLD's) are used in this work to determine TG-43 data. MCNP is also used to model a standard well chamber's response for a seed relative to both an seed and a seed. After activation, seed activity is determined using both a well chamber and a HPGe detector. The geometric variation in dose is measured using TLD's in a solid water phantom. The results for air kerma strength, per unit apparent activity, are 2.06 (MCNP) and 2.09 (measured) The former is identical to the AAPM TG-32 report results. The dose rate constant results, Λ, are 1.12 (MCNP) and 1.10 (measured) The radial dose function, anisotropy function, and anisotropy factor, are given. The anisotropy constant values are 0.973 (MCNP) and 0.994 (measured) and are consistent with both source geometry and photon energy. The calculated response of a Sun Nuclear ionization chamber, model 1008, demonstrates that to convert known and seed activities to equivalent” activities, they should be multiplied by 1.95 and 1.49, respectively.