The pulse dose rate (PDR) afterloading system is a new afterloading system which operates on the pulsed brachytherapy principle. A typical pulse length is 10 minutes, increasing to approximately 30 minutes three months later as the iridium 192 source decays. The pulse treatment is repeated each hour. The source activity is 1 Ci or less and thus the system can be installed in shielded rooms suitable for low dose rate implants. The PDR afterloading system enables equivalent continuous low dose rate treatments to be given with all the advantages of a stepping source: only one source to replace once every three months (no source inventory required), no source preparation, programmable low dose rate, optimization of dose distribution, radiation protection, patient can be disconnected between pulses, intracavitary, interstitial, intraoperative, and intralumenal treatments feasible using a single afterloader.