candidates for IORT at the time of surgery, mainly because the disease had spread to adjacent organs. This factor, combined with the risks and complexities of moving a patient during surgery, severely limited the number of patients who could be treated using the MGH method of IOERT. Consequently, conventional fractionated external beam irradiation was added to the IOERT dose, either prior to or subsequent to the surgery, in the MGH IOERT program. The National Cancer Institute (NCI) started an IOERT program in 1979. Their approach combined maximal surgical resection and IOERT and, in most cases, did not include conventional external beam therapy as part of the treatment. Because the NCI protocol relied on IOERT radiation alone, the IOERT fields were often very large, sometimes requiring two or three adjacent and overlapping fields to cover the tumor site. While the NCI results for these very large tumors were not encouraging, they showed that even the combination of aggressive surgery and large IOERT fields had acceptable toxicity. Furthermore, they introduced several technical innovations to IOERT, including the use of television for simultaneous periscopic viewing of the tumor by the surgical team. In 1981 the Mayo Clinic tried yet another arrangement. They built an OR adjacent to the radiation therapy department. Potential IOERT patients underwent surgery in the regular OR suite. If they were found to be candidates for IOERT, a second surgical procedure was scheduled in the OR adjacent to the radiation facility. By scheduling only those patients known to be suitable for IOERT, they made more efficient use of their radiation therapy machine, but at the cost of subjecting patients to a second surgery. Subsequently, the Mayo Clinic remodeled an OR and installed a conventional radiation therapy machine with its required massive shield walls, and the clinic now routinely treats over 100 IORT patients per year. After 1985, Siemens Medical Systems offered a specialized LINAC for IOERT. It was designed to be used in the OR, but it weighed more than eight tons and required about 100 tons of shielding. This proved to be too expensive an approach for the medical community, and only seven of these specialized units were ever sold. Dedicating an OR to IOERT increases the number of patients that can be treated and eliminates the risks of double surgeries and moving a patient during surgery. It also eliminates the complex logistics involved in moving patients from the