It was unclear yesterday why the new cases had not been found in the review that followed the closure of the program.
"The only thing we know so far is that they are reporting six events," said Viktoria T. Mitlyng, a spokeswoman for the commission, which oversees the medical use of radioactive materials.
The Department of Veterans Affairs, which has two weeks to file a full report, told the NRC that it was "reporting these six additional events to meet a regulatory requirement, not because of any anticipated harm to these patients."
Still, the finding of new cases now raised concerns for some members of Congress.
"Why didn't they discover it sooner?" Sen. Arlen Specter (D., Pa.), said in an interview yesterday. "Did they deliberately withhold the information?"
U.S. Rep. John Adler (D., N.J.) said he was frustrated that the VA was still finding additional errors.
"These kind of mistakes are unacceptable, and it's time for the VA to conduct a systemwide review of its practices and programs," Adler said.
The VA did not respond to requests for comment about the new cases yesterday.
In brachytherapy, physicians permanently implant in the prostate from 50 to 100 tiny metal seeds that emit radiation over a 10-month period. If improperly placed, the seeds can damage nearby organs while delivering less-than-optimal doses of radiation to the prostate.
The seed implants are usually used to treat early-stage nonaggressive cancers confined to the prostate gland. Studies show that a brachytherapy patient who receives an optimal radiation dosage has about a 90 percent chance of cure.
Experts caution that just because a treatment is classified as a "medical event" under the NRC's definition - as are the six newly identified cases - it does not necessarily mean that the patient has been harmed or that the cancer will return.
Still, the VA's top radiation oncologist told a congressional panel last month that at least six veterans given seed implants in Philadelphia had developed prostate cancer. And the treatment may also have failed for another eight men whose PSA levels - a measure of blood protein that doctors use to identify prostate cancer - are rising, Michael Hagen, the VA's national director of radiation oncology, told members of the House VA Subcommittee on Oversight and Investigations.
Federal investigators into the program identified systemic problems and failures of oversight as key reasons that the substandard treatments went undetected for so long despite numerous warning signs.
Among the problems: A computer was disconnected from the medical center's network for 14 months in 2006 and 2007, and 23 patients were treated without critical post-implant dose calculations being performed.
The VA's Philadelphia program was run by University of Pennsylvania doctors and medical physicists under a contract with the agency.
The six new cases were reported as underdoses.
That means a total of 63 veterans got too little radiation from the implants. An additional 35 patients got too much radiation to tissue and organs near their prostates, a problem that can cause serious injuries.
After the problems with Philadelphia's program were discovered, some patients were sent for additional scans to check their implants. The government also paid to have eight "grossly underdosed" men sent to Seattle to have their implants redone by the VA's top brachytherapy expert.
The additional cases reported to the NRC mean that, of all the patients in the Philadelphia program, the implants of only 16 have not been found deficient.
"I think it raises a question about what is going on with them," Specter said yesterday.