According to the May 15 letter, Chacko was placed on involuntary leave and barred from entering her Oakland office at the VA's University Drive site unless accompanied by a police escort.
Miller said the decision followed Chacko's allegations that one of her superiors, Dr. Mona Melhem, "potentially compromised patient care and subjected patients to increased doses of radiation."
"I do not ordinarily regard a personnel matter in the executive branch as a proper subject of congressional oversight," Miller said in the letter, but said he thought his intervention was justified because of "serious questions about management ... and rudimentary procedural fairness."
Chacko declined to comment.
VA spokeswoman Heather Frantz said in an e-mail: "We are not at liberty to disclose details related to this issue, due to the privacy of the employees involved."
Frantz said the VA Medical Inspector General investigated whether the radiation doses affected patient care and concluded that "no issues were identified."
Miller's letter said his subcommittee on Investigations and Oversights conducted hearings last year into another Pittsburgh VA issue — the destruction of a 30-year-old research collection of Legionella bacteria assembled by University of Pittsburgh professor Victor Yu.
"The subcommittee determined that Dr. Melhem ordered the collection destroyed out of personal animosity for the two researchers and that her explanation of her conduct to the system's chief of staff was knowingly false," Miller wrote.
Yu sued the VA. The case is pending in U.S. District Court.
Chacko's allegation about Melhem triggered her ouster, Miller said. He said Chacko accused Melhem of compromising patient care by purchasing "unsuitable radiology equipment and materials."
The dispute involved the use of a substitute radioactive material used in radiological testing, according to those familiar with the issue. Congressional aides said Miller's complaint was not the only one registered on the handling of Chacko's case.
Pittsburgh VA officials failed to follow proper procedures and did not allow Chacko to defend herself, Miller said. He said an internal report that claimed the department's performance had "begun to suffer under Chacko's leadership" was unfounded.
Chacko, 64, came to Pittsburgh from a Montana hospital. She served as a military physician in Hawaii and Texas, and worked at the Lahey Clinic in Massachusetts.
Court records show the former director of radiology in Montana charged that Chacko was involved in her wrongful discharge. Lawyers for the hospital and Chacko denied the charges.
The suit against St. James Healthcare Corp. was settled with an agreement barring all sides from discussing the settlement.