Therapeutic radiation is generally delivered in one of two ways: external beam radiation delivered by a linear accelerator, or brachytherapy, an isotope delivering radiation internally to the body. A fundamentally new way to deliver therapeutic radiation has been devised by Paul Lovoi and Tom Rusch of Xoft, Inc., Sunnyvale, Calif. The AXXENT HDR X-Ray Source, Model S700 is a micro-miniature disposable x-ray source that can be inserted into the body to deliver a 50-kVp therapeutic dose of radiation for cancer treatment. The Xoft x-ray source is similar to conventional x-ray sources, but it is only 2.25 mm in diameter and 12 mm long and has minimal shielding requirements, making it easily transportable to non-hospital locations. The Xoft x-ray source can also be moved during treatment to shape the dose distribution within a patient’s body to more flexibly conform to the region of interest around the tumor site. The radiation energy and dose rate can be varied by changing the operating voltage and beam current in the x-ray source for more detailed control of the dose distribution.