Why do patients who need focused, precise doses of radiation get walloped with huge overdoses that cause serious and even fatal injuries? A deadly combination of nonuser- friendly radiation equipment, incompatible software when machines from different manufacturers are cobbled together, user error by the technicians administering the radiation, and lax regulation by federal authorities: All these are major issues in the ongoing expose by the New York Times of malpractice issues in radiation therapy.

In the latest installment, the team led by reporter Walt Bogdanich focuses on linear accelerators, machines that originally were intended to give broad-beam radiation doses to large swaths of the body, but now are increasingly modified to deliver what are supposed to be precise, focused radiation beams. The therapy is called stereotactic radiosurgery, and it allows hospitals who lack the more expensive competitor device, gamma knife surgery, to compete for radiation therapy business when the patient needs a very focused, intense dose to sensitive tissue -- such as a nerve deep in the brain.