declare 
  v_val varchar2(10) := 't';
begin 
  dbms_aqadm.purge_queue_table('MYQT','QTVIEW.USER_DATA.SOME_NAME='''||v_val||'''', null);
end;  

declare 
 opts dbms_aqadm.aq$_purge_options_t;
 v_val varchar2(10) := 't';
begin 
  dbms_aqadm.purge_queue_table('MYQT','QTVIEW.USER_DATA.SOME_NAME='''||v_val||'''', opts);
end;