Supporters of Prouty Garden — a historic healing garden for patients at Boston Children's Hospital — are asking state officials to re-consider their approval of a planned hospital expansion that would see the garden demolished.

The billion-dollar project received final approval from the Department of Public Health's Public Health Council in October. On Thursday, supporters of Prouty Garden filed an administrative appeal of that Public Health Council decision.

Under the expansion, the half-acre garden would be replaced with a new 11-story clinical building housing 71 single-bed units and a new neonatal intensive care unit.

Hospital officials say the expansion is needed to replace outdated facilities and to increase the amount of space available at the hospital. Opponents of the plan have said that Prouty Garden is an important part of the care the hospital gives its patients.

Critics have also raised concerns that the project would make health care costs in the state rise as patients leave smaller hospitals to move to the expanded Boston Children's. An analysis by state watchdog agency Health Policy Commission agreed with that claim -- while a DPH assessment found costs would not rise.

In the appeal, supporters of the garden say the Public Health Council and the Department of Public Health granted approval to the project without sufficiently reviewing the hospital's application. They also say DPH did not state the exact reasons for approving the expansion and that the department did not follow proper procedures.

In a statement, Boston Children's Hospital says they earned approval at every step of the planning process. The hospital says they received DPH approval after they "demonstrated a clear need for its clinical care."