On the physical, spectral, and dosimetric characteristics of a new brachytherapy source

Abstract

A new 125I source under the name Braquibac has been developed in Argentina for interstitial brachytherapy applications. The aim of this work is to study the new seed's design and to calculate its dosimetric parameters. Radiographic and destructive tests were carried out on inactive seeds to determine the physical characteristics of the source. Values of g(r), Lambda, F(r, Theta), and phi(an)(r), were obtained in water and air by simulation using the MCNP5 Monte Carlo code according to the methodology recommended in TG-43 and updated in TG-43U1. The dose rate constant was determined to be 0.937+/-0.004 cGy h(-1) U(-1) (overall statistical uncertainty +/-2.7%). Sk per unity activity was calculated to be 0.671+/-0.003 cGy cm2 h(-1) mCi(-1) by simulation of the seed in dry air using point detectors. Spectroscopic studies for both the new and the Amersham model 6711 seed were performed using an HPGe planar detector. The emission spectra of both seeds proved to be very similar. The anisotropy of the total photon intensity in air was measured in planes containing the seed's short and long axes using the HPGe detector. The minimum photon intensity for the new seed was 31.14+/-3.10% of the transverse intensity.

An EGSnrc Monte Carlo‐calculated database of TG‐43 parameters

“…Dimensions for the Braquibac source 31 are taken from the study by Pirchio et al 31 The source element for the Braquibac seed is a cylindrical silver rod with an outer diameter of 0.500 mm and a length of 3.07 mm. The rod is coated with a silver halide layer that is 1.00 m thick.…”

“…The Braquibac seed shows a 3.5% variation in the dose rate constant calculated using different voxel sizes for scoring air-kerma strength because it contains a right circular cylindrical source element. Pirchio et al 31 published a value of ⌳ = 0.937͑4͒ cGy h −1 U −1 for the dose rate constant based on an extrapolation of the air-kerma strength along the transverse axis. 31 The value from Pirchio et al 31 is 1.2% lower and 2.2% greater than the values of ⌳ = 0.949͑3͒ cGy h −1 U −1 and ⌳ = 0.917͑3͒ cGy h −1 U −1 calculated in this study using the point and WAFAC voxels, respectively.…”

“…Pirchio et al 31 published a value of ⌳ = 0.937͑4͒ cGy h −1 U −1 for the dose rate constant based on an extrapolation of the air-kerma strength along the transverse axis. 31 The value from Pirchio et al 31 is 1.2% lower and 2.2% greater than the values of ⌳ = 0.949͑3͒ cGy h −1 U −1 and ⌳ = 0.917͑3͒ cGy h −1 U −1 calculated in this study using the point and WAFAC voxels, respectively. This means our best calculation of the dose rate constant is 2.2% lower than the only dose rate constant currently available for this source.…”