Beta versus gamma dosimetry close to Ir‐192 brachytherapy sources

Abstract

The relative importance of the dose rate component owing to the beta spectrum emitted by 192Ir brachytherapy sources at the short radial distances of interest in intravascular and endobronchial applications is investigated. Separate dosimetric calculations, using Monte Carlo simulations, were performed for the gamma and beta dose rate components of an 192Ir ideal point source as well as real 192Ir source designs used in clinical practice including wire and seed sources and both Nucletron and Varian, old and new, high dose rate (HDR) source designs. A significant dose rate enhancement due to the beta spectrum emitted by 192Ir, greater than 50% for radial distances r<2 mm, was observed for an ideal point source. For real source designs, however, the magnitude of this enhancement was found to depend strongly on the sources' geometric as well as compositional details of the active core and encapsulation. A detectable effect was found for the majority of the investigated sources at radial distances less than 1 mm, but overall findings suggest that the contribution of beta particles is not significant in 192Ir clinical intravascular applications that are currently carried out. However, since treatment of vessels with smaller diameters, in the future, may lead to the development of 192Ir sources and catheters of reduced diameters, the potential effect of the beta spectrum in terms of dose enhancement to tissues in close proximity to 192Ir sources should not be ignored.

Effect of inhomogeneities and source position on dose distribution of nucletron high dose rate Ir-192 brachytherapy source by Monte Carlo simulation

“…The beta spectrum of the Ir source has not been considered in simulation since its contribution to the dose rate distribution for distances greater than 1 mm from the source is negligible due to the encapsulation of the source and the catheter in which the source is introduced. [11] However, the models for the processes of Compton scattering, Photoelectric effect and Rayleigh scattering have been used from the low energy package of EGSnrc. The cross-section tabulation was taken from the EPDL 97.…”

A dosimetric uncertainty analysis for photon‐emitting brachytherapy sources: Report of AAPM Task Group No. 138 and GEC‐ESTRO

“…Further, electron dose contributions from sources generally considered as photon emitters should be considered. [48][49][50] The National Nuclear Data Center ͑NNDC͒ at Brookhaven National Laboratory is an internationally regarded reference for radionuclide radiation spectra. 51 This database includes all of the commonly used radionuclides in brachytherapy, often listing the precision of photon and electron energies to four significant digits and the emission intensities to three significant digits and probabilities to parts per million.…”

Monte Carlo study of dosimetric parameters and dose distribution effect of inhomogeneities and source position of GammaMed Plus source

“…The beta spectrum has not been considered in simulation since it's contribution to the dose rate distribution for distances greater than 1 mm from the source is negligible due to the encapsulation of the source and the catheter in which the source is introduced. [16] However, the models for the processes of Compton scattering, Photoelectric effect and Rayleigh scattering have been used simulated in the low energy package of EGSnrc. The cross-section tabulation with uncertainty was taken from the EPDL 97.…”