The microwave electron linac in the treatment of cancer

Immediately after the discovery of X-rays at the end of the nineteenth century the enormous medical value of ionizing radiation was clear. Radiation has certain unique properties for cancer treatment not duplicated by any other modality. In the modern clinical setting more than half of all cancer patients are treated with radiation and this percentage is increasing with the availability of new techniques. X-rays dominate with electrons used in 5 to 10 percent of the cases and other kinds of radiation playing a peripheral role. An extraordinary effort went into the search for the optimum radiation treatment machine during the twentieth century. Microwave electron linacs producing bremsstralung beams of 4 to 6 megavolts and versions producing bremsstralung beams from 4 to 25 MV, with ancillary electron beams from 4 to 20 MeV, have emerged as the overwhelming treatment system of choice. Today these machines are computer controlled and can provide advanced dose shaping capabilities with the use of dynamic Multi-Leaf Collimators, MLC's in conjunction with specialized dose planning systems. WHO statistics indicate a doubling of cancer incidence and mortality by the year 2020 and an increasing need for such equipment. Commercially available medical linacs are impressively robust and extraordinarily cost effective and are used extensively in both developed and developing countries.