public void PopulateDoctorDropdownList()
{
int centerId = Convert.ToInt32(Session["centerId"]);
doctorDropDownList.DataSource = manager.PopulateDoctorDropDownList(centerId);
doctorDropDownList.DataTextField = "DoctorName";
doctorDropDownList.DataValueField = "Id";
doctorDropDownList.DataBind();
}