High dose rate (HDR) brachytherapy involves the placement of a single, computer-controlled radioactive source in or near a tumor, or near regions suspected to harbor cancerous cells. The high activity of the source means that high doses of radiation can be delivered in minutes, typically as outpatient therapy. Because the source can be moved precisely within the region of concern, it allows radiation oncologists to deliver highly concentrated doses of radiation to a tumor while sparing normal tissues.

HDR brachytherapy is commonly used for many tumors, including those involving the lung, breast, uterus and cervix. Often the treatments are combined with external beam radiation, allowing radiation oncologists to create the optimal plan for therapy customized to each patient.