Brachytherapy (HDR & LDR) Brachytherapy is a method of delivering radiation to tumors by placing radioactive sources either within or immediately adjacent to tumor tissue. Because the radiation source is very close to the tumor, therapeutic radiation can affect the tumor directly while minimally affecting normal tissue. Brachytherapy can be provided using low dose rate (LDR) or high dose rate (HDR) techniques, depending on the length of time the radioactive sources remain in place.