For patients with prostate cancer, it is a common surgical procedure: a doctor implants dozens of radioactive seeds to attack the disease. But when Dr. Gary D. Kao treated one patient at the veterans’ hospital in Philadelphia, his aim was more than a little off.

Most of the seeds, 40 in all, landed in the patient’s healthy bladder, not the prostate.

It was a serious mistake, and under federal rules, regulators investigated. But Dr. Kao, with their consent, made his mistake all but disappear.

He simply rewrote his surgical plan to match the number of seeds in the prostate, investigators said.

The revision may have made Dr. Kao look better, but it did nothing for the patient, who had to undergo a second implant. It failed, too, resulting in an unintended dose to the rectum. Regulators knew nothing of this second mistake because no one reported it.

Two years later, in 2005, Dr. Kao rewrote another surgical plan after putting half the seeds in the wrong organ. Once again, regulators did not object.

Had the government responded more aggressively, it might have uncovered a rogue cancer unit at the hospital, one that operated with virtually no outside scrutiny and botched 92 of 116 cancer treatments over a span of more than six years — and then kept quiet about it, according to interviews with investigators, government officials and public records.

The team continued implants for a year even though the equipment that measured whether patients received the proper radiation dose was broken. The radiation safety committee at the Veterans Affairs hospital knew of this problem but took no action, records show.

One patient was the Rev. Ricardo Flippin, a 21-year veteran of the Air Force. “I couldn’t walk and I couldn’t stand,” he said, citing rectal pain so severe that he had to remain in bed for six months, losing his church job and his income.

Pastor Flippin first learned of what his doctors called a radiation injury not from the V.A., but from an Ohio hospital where he underwent rectal surgery in 2006 to treat the damage. “There are times when I don’t have control over my bowels,” he said one recent Sunday, after excusing himself during a service at a church in West Virginia where he now preaches.

The 92 implant errors resulted from a systemwide failure in which none of the safeguards that were supposed to protect veterans from poor medical care worked, an examination by The New York Times has found.

Peer review, a staple of every good hospital, in which colleagues examine one another’s work, did not exist in the unit. The V.A.’s radiation safety program; the Nuclear Regulatory Commission, which regulates the use of all nuclear materials; and the Joint Commission, a group that accredited the hospital, all failed to intervene; either their inspections had been limited or they had not acted decisively upon finding problems.

Over all, the implant program lacked a “safety culture,” the nuclear commission found. Dr. Kao and other members of his team, the commission said, were not properly supervised or trained in what constitutes a substandard implant and the need to report it. Dr. Kao declined to comment for this article.

Virtually none of the substandard implants in Philadelphia were reported to the nuclear commission, meaning errors went uninvestigated for weeks, months and sometimes years. During that time, many patients did not know that their cancer treatments were flawed.

Federal investigators are continuing to look into the flawed implants as well as those at other V.A. hospitals. The Philadelphia prostate unit was closed after problems began to surface in mid-2008, and it has yet to reopen. The V.A. has also suspended the implants, known as brachytherapy, at hospitals in Jackson, Miss., and Cincinnati, though neither had problems on a scale of Philadelphia’s.

The V.A. has yet to fully account for how these substandard implants affected veterans, though no one is believed to have died from them. No patient names have been made public. Veterans officials said Dr. Kao was no longer at the Philadelphia hospital and would not be allowed to return. The officials acknowledged that they had failed to supervise the unit.

A lawyer for Dr. Kao, Jack L. Gruenstein, said The Times’s account of the doctor’s role was “false,” but he declined to elaborate.

A nuclear commission consultant, Dr. Ronald E. Goans, reviewed about a quarter of the substandard implants and reported that “erratic seed placement caused a number of cases to have elevated doses to the rectum, bladder or perineum.” After learning of the problems, the V.A. flew seven patients treated in Philadelphia to its most experienced brachytherapy program in Seattle for additional implants.

“I’m not easily shaken,” Dr. Leon S. Malmud, chairman of a nuclear commission advisory committee, said last month after investigators briefed the panel on their findings in Philadelphia. “But this is a very anxiety-provoking story.”

Clues That All Is Not Right

The brachytherapy program at the Philadelphia V.A. hospital began in early 2002, giving veterans an option for treating prostate cancer without major surgery. In this procedure, metal seeds the size of a grain of rice are permanently inserted into the prostate through needles.

“The idea is to create a radioactive cloud that conforms to and treats the prostate,” said Dr. Louis Potters, department chairman of radiation medicine at North Shore Long Island Jewish Health System.

By using ultrasound in the operating room, Dr. Potters can assess how well radiation is being distributed. “So at the completion of the case,” he said, “I can go out and tell that patient’s wife or significant other that we did a very good implant.”

And good implants were what the Philadelphia V.A. expected when it staffed the new unit with outside contractors from an Ivy League institution, the University of Pennsylvania School of Medicine.

One contractor was Dr. Kao. In addition to his work as a cancer researcher, he had a medical degree from Johns Hopkins and a Ph.D. from Penn. He is also on a team from Penn that won a contract this year from a NASA-financed consortium to study radiation in space.

Although Dr. Kao was board certified in radiation oncology, he had limited experience in brachytherapy, according to the nuclear commission. Even so, the unit had no peer review.

“In every facility that I’ve ever practiced and seen, there is some form of peer review going on,” said Dr. James Welsh, a radiation oncologist and member of the nuclear commission’s advisory board.

It was not long before problems began to surface. In the first year, nine implants were substandard, including two on the same day, records show.

In early 2003, the V.A. and the nuclear commission got their first solid clue that all was not right in the cancer unit.

On Feb. 3, Dr. Kao mistakenly implanted more than half the seeds in a patient’s bladder. With the patient still under anesthesia, a urologist had to thread a small tube through the man’s penis to retrieve the 40 errant seeds. Because they were bloody and contaminated with urine, the seeds could not be reused, and no more were available.

As a carcinogen that can burn healthy tissue as well as kill cancerous cells, radiation is supposed to be closely monitored. The hospital’s radiation safety committee handles regulatory issues. The V.A.’s National Health Physics Program oversees radiation use in all veteran facilities.

But the chief regulator is the Nuclear Regulatory Commission. Serious accidents involving radioactive materials must be reported to that agency, which has the power to investigate and levy fines. Congress receives an annual list of those accidents.

After learning of Dr. Kao’s error, V.A. officials thought that because he had revised his surgical plan while still in the operating room, the mistake did not exist. The nuclear commission agreed, on the ground that doctors needed freedom to revise their surgical plan depending on what they found during surgery.

Yet this case did not involve a new diagnostic interpretation: it was an implant mistake, causing the patient to return for another procedure.

Dr. Charles M. Anderson, who heads the V.A.’s national radiation safety committee, said it was “not good medical practice” to have to redo surgery.

Asked whether Dr. Kao was trying to cover up a mistake, Dr. Anderson said, “I’m not going to look into this guy’s soul.”

The Nuclear Regulatory Commission lacked the authority to challenge Dr. Kao’s revisions, said Steven A. Reynolds, director of nuclear materials safety for the commission. “The N.R.C. isn’t in the business of practicing medicine,” Mr. Reynolds said.

The two incidents in Philadelphia have prompted the N.R.C. staff to propose allowing revisions to surgical plans only before an implant is done.

One Patient’s Case

When Pastor Flippin arrived for his implant in May 2005, he was unaware that brachytherapy errors at the Philadelphia V.A. were piling up.

He had traveled to Philadelphia from West Virginia to care for his elderly mother. “I felt I had been neglectful in my relationship with my mother,” said Pastor Flippin, 68. Now he wanted to make things right. “The best way to do that was to go back and be with her,” he said.

After learning that he had prostate cancer, Pastor Flippin picked brachytherapy rather than external beam radiation or surgery. The doctor’s words were especially comforting, he said.

“I remember him telling me that it was a relatively safe procedure that he had done — and I was impressed with this — he had done over 600 seed implants, that there was nothing to worry about,” Pastor Flippin said in an interview last month.

Pastor Flippin’s medical records show that he was counseled by the other doctor in the unit, Dr. Richard Whittington, then chief of radiation oncology at the Philadelphia V.A. and now a professor at Penn’s medical school, a V.A. official said.

But Dr. Kao did the implant, the records show. Investigators say he is responsible for all but a handful of the 92 substandard implants at the Philadelphia V.A. Dr. Whittington declined to be interviewed.

At first, Pastor Flippin’s implant seemed fine. But 10 months later, he said, he began experiencing bowel pain that worsened with time. Now back in West Virginia, Pastor Flippin sought treatment at a V.A. hospital in Huntington. Doctors there suspected constipation, hemorrhoids or gas.

“They gave me suppositories, they gave me flushings, they gave me a rinse where you sit in and everything else,” Pastor Flippin said. “I’m saying none of this is working.”

Doctors then prescribed narcotics. “It was just a succession of painkiller after painkiller after painkiller, and it got to the point where I said, ‘I don’t want any more morphine,’ ” Pastor Flippin said. His weight dropped to 109 pounds, a 20 percent loss. He had to quit his job coordinating after-school programs for a coalition of churches in Charleston, W.Va.

“This is not working,” he told his doctors. “I’m barely alive, I’m wasting away and you all are not doing anything.”

Increasingly desperate, Pastor Flippin sought help from the Ohio State University Medical Center, where a doctor finally made a diagnosis: “Radiation injury to anal canal,” he wrote. Surgery was performed to cover the damaged area with a tissue flap.

It would be another year and a half before a letter from the V.A. arrived, informing Pastor Flippin in August 2008 that he had received a flawed implant. “The treatment you received did not meet V.A.’s high standard of care,” the letter said.

At this point, it hardly mattered that the V.A. rendered Pastor Flippin’s first name wrong, calling him Richard, rather than Ricardo.

A Discovery Leads to Others

The substandard implants might never have been discovered were it not for a clerical error.

In the spring of 2008, a radiation safety official at the V.A. mistakenly ordered seeds of lower strength, and they were implanted.

After the error was discovered, according to the nuclear commission, the V.A.’s national radiation safety unit asked the hospital to examine 10 to 20 more cases to see if the problem had occurred before.

It had not. But investigators found something more troubling: four instances where seeds were implanted in the wrong places. As more cases were examined, more mistakes were found.

“Every once in a while you’re going to have a medical event because the seed will migrate, but when you see more than one or two at one place, we’re like: ‘What’s going on? Is this a pervasive problem?’ ” said Mr. Reynolds, the nuclear commission official.

The hospital suspended the brachytherapy program on June 11 last year. By then, 45 substandard implants had been found.

Two days later, the Joint Commission, which helps set standards in the hospital industry, surveyed the Philadelphia V.A. and on the next day accredited the hospital. “This organization is in full compliance with applicable standards,” the Joint Commission said.

The commission said that it had no indications of the problems in the brachytherapy program when it arrived at the hospital and that its surveys are not detailed enough to have uncovered the flawed implants.

Soon after, the N.R.C. sent its own inspectors to Philadelphia. And the more the inspectors looked, the more they found. All told, 57 of the implants delivered too little radiation to the prostate, either because the seeds missed the prostate or were not distributed properly inside the prostate. Thirty-five other cases involved overdoses to other parts of the body. An unspecified number of patients were both underdosed in the prostate and overdosed elsewhere.

From December 2006 to November 2007, the nuclear commission found, 16 patients received seed implants in Philadelphia even though computer interface problems prevented medical personnel from determining whether those treatments had been successful. The V.A.’s radiation officials knew of the problem but took no action, the nuclear commission charges.

Investigators said they did not know how the unit made so many mistakes or why Dr. Kao decided to rewrite only two surgical plans. The doctors, according to the nuclear commission, believed “that since the patients were not having complications, the implant quality must be acceptable.”

The V.A. put too much trust in the contractors, said Darrell G. Wiedeman, a senior health physicist for the nuclear commission. “They claim they hired experts, the best that money could buy from the local university, so therefore they didn’t require a lot of training and oversight,” Mr. Wiedeman said at a recent meeting of the nuclear commission’s advisory board.

Susan Phillips, a senior executive at Penn’s medical school and health system, said Dr. Kao had voluntarily given up his clinical privileges there, though he continues to do research on campus. Dr. Kao did an unspecified number of brachytherapy procedures at the campus hospital with no apparent problems. A check of state and federal records over the last decade in Pennsylvania turned up no malpractice or disciplinary actions against Dr. Kao.

Back in West Virginia, Pastor Flippin said he continued to try to build up his small church while dealing with the side effects of his implant. After 21 years of serving his country, he had hoped for a better ending.

“It’s not fair,” he said. “Any veteran should expect more than what we’re getting.”