[otrs] hiding subject field

Hello list, We are configuring OTRS 2.3.4 and in the customer´s page, when clicked one of the user´s tickets, another view shows the details and messages exchanged regarding that ticket. On the bottom of the page, there are 2 fields, one for the subject and another for entering a text. What we want to do is to hide or disable the subject field in order to avoid changing of the subject after the ticket creation. Searched on the net, manuals and SYSCONFIG but could not find something on this yet. Is it possible? How it can be done? Thanks you all in advance. Mauricio.