Original paper
Evaluation of ¹⁰¹Rh as a brachytherapy source

Purpose: Recently a number of hypothetical sources have been proposed and evaluated for use in brachytherapy. In the present study, a hypothetical ¹⁰¹Rh source with mean photon energy of 121.5 keV and half-life of 3.3 years, has been evaluated as an alternative to the existing high-dose-rate (HDR) sources. Dosimetric characteristics of this source model have been determined following the recommendation of the Task Group 43 (TG-43) of the American Association of the Physicist in Medicine (AAPM), and the results are compared with the published data for ⁵⁷Co source and Flexisource ¹⁹²Ir sources with similar geometries.

Material and methods: MCNPX Monte Carlo code was used for simulation of the ¹⁰¹Rh hypothetical HDR source design. Geometric design of this hypothetical source was considered to be similar to that of Flexisource ¹⁹²Ir source. Task group No. 43 dosimetric parameters, including air kerma strength per mCi, dose rate constant, radial dose function, and two dimensional (2D) anisotropy functions were calculated for the ¹⁰¹Rh source through simulations.

Results: Air kerma strength per activity and dose rate constant for the hypothetical ¹⁰¹Rh source were 1.09 ± 0.01 U/mCi and 1.18 ± 0.08 cGy/(h.U), respectively. At distances beyond 1.0 cm in phantom, radial dose function for the hypothetical ¹⁰¹Rh source is higher than that of ¹⁹²Ir. It has also similar 2D anisotropy functions to the Flexisource ¹⁹²Ir source.

Conclusions: ¹⁰¹Rh is proposed as an alternative to the existing HDR sources for use in brachytherapy. This source provides medium energy photons, relatively long half-life, higher dose rate constant and radial dose function, and similar 2D anisotropy function to the Flexisource ¹⁹²Ir HDR source design. The longer half-life of the source reduces the frequency of the source exchange for the clinical environment.