How to Read XML String and Create XML File in Asp.net

SqlCommand cmd = new SqlCommand("Select top 10 * from TblAppointment", con);
        con.Open();
        SqlDataAdapter da = new SqlDataAdapter(cmd);
        DataSet ds = new DataSet();
        da.Fill(ds);

        XmlDocument doc = new XmlDocument();

        foreach (var XML in ds.Tables[0].AsEnumerable())
        {
            doc.LoadXml(XML.Field<string>("AppointmentTransXml"));

            doc.Save(Server.MapPath("XML") + "//" + XML.Field<string>("Patientname") + ".xml");
        }