They learned this by observing skin disease in outdoor workers and lung cancer in uranium miners in the 18th and 19th centuries. But physicians soon realized that radiation's energy could be used to cure diseases as well. In 1899, doctors used radiation to treat a malignant tumor of the nose, and their patient was disease-free more than 20 years later. More with Less Cancerous tumors contain large numbers of dividing cells, which multiply often and lead to tumor growth. Focused doses of radiation disrupt those cell divisions, and can cause cancer cells to die.
Radiation oncologists combine computer imaging with machines called multi-leaf collimators.
These are the devices that actually direct a beam of radiation at a cancerous mass, while guarding against exposing normal tissue to potentially damaging radiation. Until a few years ago, it was standard practice for technicians to place bulky blocks of lead in the path of the collimator beam in order to protect healthy tissue. The process was cumbersome and dangerous, since an inadvertently dropped block could injure a patient or technician. No weighty blocks to install, no dangerous lead to carry around. EBT is combined with computerized imaging in three-dimensional field shaping, a method of modeling the area of the body in which the therapeutic radiation is focused, even with tumors of irregular shape.