A former Manassas orthopedic surgeon was convicted yesterday of defrauding cancer patients whom he treated intravenously with an unapproved aloe vera substance.

Donald L. MacNay--four of whose patients died shortly after receiving the treatments--was convicted of obtaining money by false pretenses in one case and of attempting to do so in another. He still faces federal charges of fraud and other violations, and a trial is set for March in Baltimore.

Yesterday's convictions came after MacNay, 62, of Leesburg, entered Alford pleas, in which he did not admit guilt but acknowledged that prosecutors had enough evidence to gain a conviction.

Prince William County Circuit Court Judge Richard B. Potter set sentencing for Dec. 16. MacNay could receive up to 30 years in prison, but under the plea agreement, Commonwealth's Attorney Paul B. Ebert recommended that Potter follow the state's sentencing guidelines, which call for probation. MacNay will remain free on bond until his sentencing.

Ebert said yesterday's plea agreement spares the families of MacNay's patients the pain of testifying twice--once at a Prince William County trial and again in federal court.

"His plea today saved the families a lot of grief," Ebert said. "It has been nightmarish for them since the treatments started."

Assistant Commonwealth's Attorney Mary Grace O'Brien said yesterday's conviction will make it easier to prosecute MacNay on the federal charges.

In July, a federal grand jury in Baltimore indicted MacNay, his Baltimore distributor and an Oklahoma manufacturer on charges of conspiracy, fraud and introducing an unapproved drug into interstate commerce.

According to prosecutors, MacNay bilked patients of thousands of dollars in 1997 by selling them a "miracle cure" that he claimed was approved by the Food and Drug Administration. MacNay administered intravenous doses of an aloe vera-based substance, marketed under the name "T-Up," at his Piedmont Clinic in Manassas.

MacNay and his attorneys declined to comment after yesterday's hearing, and MacNay's only statement to the court was that "it would be questionable" whether he would have been able to defend himself given the evidence against him.

Authorities became aware of the treatments in May 1997, after one of MacNay's patients, Clarence Holland Lander, 82, of Waco, Tex., died in MacNay's office.

Three other patients died shortly after receiving similar treatments from MacNay.

Ebert said authorities have not pursued murder or manslaughter charges against MacNay because authorities have not been able to determine that the aloe treatments directly led to his patients' deaths.

Virginia State Police special agent David Huff testified that the causes of death have been left "undetermined" because each of the patients was terminally ill and may have died of natural causes.

Yesterday's conviction related to four patients MacNay treated in 1997, two of whom paid MacNay and two of whom either didn't pay or were refunded their money.

Huff testified yesterday that patients and their families had paid MacNay as much as $15,000 for two weeks of intravenous treatments, and one woman paid him $4,250 in cash for one treatment, which MacNay later refunded.