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 electron energy, 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 (EBR) because it results in less integral doses and shorter treatment times. Medical uses IOERT has a long history of clinical applications, with promising results, in the management of solid tumors (e.g., pancreatic cancer, locally advanced and recurrent rectal cancer, breast tumors, sarcomas, and selected gynaecologic and genitourinary malignancies, neuroblastomas and brain tumors. In virtually every tumor site, electron IORT improves local control, reducing the need for additional surgeries or interventions. The following is a list of disease sites currently treated by IOERT: Breast cancer Since 1975, breast cancer rates have declined in the U.S., largely due to mammograms and the use of adjuvant treatments such as radiotherapy. Local recurrence rates are greatly reduced by postoperative radiotherapy, which translates into improved survival: Preventing four local recurrences can prevent one breast cancer death. In one of the largest published studies so far called (ELIOT), researchers found that after treating 574 patients with full-dose IOERT with 21 Gy, at a median follow-up of 20 months, there was an in-breast tumor recurrence rate of only 1.05%. Other studies show that IOERT provides acceptable results when treating breast cancer in low-risk patients. More research is needed for defining the optimal dose of IOERT, alone or in combination with EBRT, and for determining when it may be appropriate to use it as part of the treatment for higher risk patients. Colorectal cancer Over the past 30 years, treatment of locally advanced colorectal cancer has evolved, particularly in the area of local control – stopping the spread of cancer from the tumor site. IOERT shows promising results. When combined with preoperative external beam irradiation plus chemotherapy and maximal surgical resection, it may be a successful component