Government regulators have been slow to respond. Radiation accidents are chronically underreported, and a patchwork of laws to protect patients from harm are weak or unevenly applied, creating an environment where the new technology has outpaced its oversight, where hospitals that violate safety rules, injure patients and fail to report mistakes often face little or no punishment, The New York Times has found.

In this largely unregulated marketplace, manufacturers compete by offering the latest in technology, with only a cursory review by the government, and hospitals buy the equipment to lure patients and treat them more quickly. Radiation-generating machines are so ubiquitous that used ones are even sold on eBay.

“Vendors are selling to anyone,” said Eric E. Klein, a medical physicist and professor of radiation oncology at Washington University in St. Louis. “New technologies were coming into the clinics without people thinking through from Step 1 to Step 112 to make sure everything is going to be done right.”

A national testing service recently found unacceptable variations in doses delivered by a now common form of machine-generated radiation called Intensity Modulated Radiation Therapy, or I.M.R.T. To help institutions achieve more consistency, an association of medical physicists issued new I.M.R.T. guidelines in November.

The problems also extend to equipment used to diagnose disease.

More than 300 patients in four hospitals  and possibly many more  were overradiated by powerful CT scans used to detect strokes, government health officials announced late last year. The overdoses were first discovered at Cedars-Sinai Medical Center, a major Los Angeles hospital, where 260 patients received up to eight times as much radiation as intended.

Those errors continued for 18 months and were detected only after patients started losing their hair. The federal Food and Drug Administration is still struggling to understand and untangle the physics underlying the flawed protocols. The F.D.A. has issued a nationwide alert for hospitals to be especially careful when using CT scans on possible stroke victims.

Although the overdoses at Cedars-Sinai were displayed on computer screens, technicians administering the scans did not notice. In New York City, technologists who also did not watch their treatment computers contributed to two devastating radiation injuries documented in an article in The Times on Sunday.