get access to define() constants with dynamic names

Hi all, my script knows three different constants

define(G_T_USER,        "user_profile");
define(G_T_TEAM,        "SAFETOUR_team");
define(G_T_CALL,        "SAFETOUR_call");

Is it possible to get access to them, if I have the names (USER, TEAM, CALL) in a variable? It must be something like that: aName = "TEAM"; myString = "G_T_$sName"; // myString = "SAFETOUR_team" Any hint to solve this problem would be useful. heiko