The 23 mev betatron has been in medical use at the University of Illinois since 1949. It is our experience that the majority of the medical profession has still only very vague ideas about the clinical possibilities and limitations of this megavoltage therapy. I try to outline here our present views about the possible indications and expectations after seven years' experience.
When we started we did not expect a dramatic change in cancer cure by the use of the new type of radiation. From a pathological point of view, the irradiation is a local treatment, while the cancer is very frequently a systemic disease at the time of the irradiation. Either it is multifocal in origin, or cancer cells have already spread into the lymphatic or vascular pathways of generalization. A local treatment cannot cure a cancer which is not localized. From a biophysical point of view, the biological effect