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A Michigan oncologist who inflicted excessive and painful cancer treatments on hundreds of patients — many of whom didn't have the disease in the first place — sobbed as he was sentenced Friday to spend what will likely be the rest of his life in prison, capping an emotional week in which a procession of victims told a federal judge how the scams had ravaged their bodies.

Farid Fata, who operated the racket from an empire of upscale clinics in the Detroit suburbs, began weeping before the punishment was even handed down.

Speaking publicly for the first time since his August 2013 arrest, Fata blamed greed and a "self-destructive" thirst for power.

"They came to me seeking compassion and care. I failed them," he told U.S. District Judge Paul Borman, his tear-choked voice barely intelligible before an overflow audience in a Detroit federal courtroom.

The disgraced doctor turned to his victims and apologized, which he admitted wasn't enough. "My sins are many," he said.

Fata asked Borman for mercy. But a prosecutor reminded the judge of the victims' "lifetime of suffering."

The judge, calling Fata's crimes "huge" and "horrific," deliberated for about an hour before sentencing Fata to 45 years behind bars.

By then, Fata's tears were gone. He stared ahead, looking emotionless.

His victims, many of whom wore bright yellow to the sentencing to symbolize the last day Fata would see the sun, remained quiet in the courtroom. Afterwards, their disappointment and anger spilled out.

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"It's not enough," said Geraldine Parkin, whose husband underwent unneeded chemotherapy.

She, like many others, wanted the judge to impose the maximum possible sentence of 175 years; Fata's lawyers had asked for 25.

"We expected more," said Steve Flagg, whose wife, Monica, testified about learning of her misdiagnosis after her leg snapped in half.

As for Fata's tears, Flagg said: "It was just a show."

Authorities said they, too, were disappointed in the length of the prison term, but felt confident that it would encompass all, or most, of his life.

U.S. Attorney Barbara McQuade of the Eastern District of Michigan called Fata's scheme "the most serious fraud case in the history of the country." No prior investigation, she said, included "the kind of stunning physical harm that we saw in this case."

Noting that chemotherapy is toxic to both cancerous and healthy tissue, McQuade said Fata "gave poison to these people not to keep them alive but to make money."

Paul Abbate, the special agent in charge of the FBI's Detroit office, said Fata "has a place among the worst of the worst offenders," in large part because he exploited victims' will to live.

Fata, 50, who is married with children, pleaded guilty in September to an array of criminal charges, including health care fraud, money laundering and seeking kickbacks. In court papers, prosecutors said he scammed more than 500 patients, telling some they had cancer when they did not, giving too much or improper treatment to those who did, and persisting with painful and dangerous chemotherapy treatments who no longer needed it.

Prosecutors likened Fata to a medical version of convicted Ponzi scammer Bernard Madoff and accused him of bullying patients into dangerous treatments that underwrote an opulent lifestyle.

About two dozen of them took the stand in court this week to testify about how Fata had stolen their health, money and trust. They spoke of the fear of dying, and of unneeded chemotherapy wracking their bodies and leaving chronic health problems.

Some have filed a civil suit, hoping that it will draw out more information about the case, including including why Fata's practices did not come to light sooner.

Federal authorities were alerted to the situation through a whistle-blower suit filed by the doctor's office manager, George Karadsheh, who said he started digging as soon as he heard disturbing things about misdiagnosis and overtreatment.

That tip came on a Friday, McQuade said. Four days later, investigators had enough evidence to shut down his offices.

Contacted after the sentencing, Karadsheh told NBC News, "I feel very sad for the victims, because they will go on feeling pain and suffering as a result of Fata long after the sentence is over."

The victims, along with Karadsheh, will be entitled to share in forfeiture proceeds from Fata, McQuade said.

But they are also looking for more, through civil filings.

"Our case," a lawyer representing several victims said, "is just beginning."