Intraoperative electron radiation therapy is the application of electron radiation directly to the residual tumor or tumor bed during cancer surgery. Electron beams are useful for intraoperative radiation treatment because, depending on the , the dose falls off rapidly behind the target site, therefore sparing underlying healthy tissue. IOERT has been called "precision radiotherapy," because the physician has direct visualization of the tumor and can exclude normal tissue from the field while protecting critical structures within the field and underlying the target volume. One advantage of IOERT is that it can be given at the time of surgery when microscopic residual tumor cells are most vulnerable to destruction. Also, IOERT is often used in combination with external beam radiotherapy (EB