Comparison of 60cobalt and 192iridium sources in high dose rate afterloading brachytherapy

(60)Co sources with dimensions identical to those of (192)Ir have recently been made available in clinical brachytherapy. A longer half time reduces demands on logistics and quality assurance and perhaps costs.

Comparison of the physical properties of (60)Co and (192)Ir with regard to brachytherapy.

Required activities for the same air kerma rate are lower by a factor of 2.8 for (60)Co. Differential absorption in tissues of different densities can be neglected. Monte Carlo calculations demonstrate that integral dose due to radial dose fall off is higher for (192)Ir in comparison to (60)Co within the first 22 cm from the source (normalization at 1 cm). At larger distances this relationship is reversed.

Clinical examples for intracavitary and interstitial applications however, show practically identical dose distributions in the treatment volume.