Also keep in mind that in most contexts, relating to surgery, elective and voluntary are indistintly used.
<hr> According to the rest of the text you will have to decide if this is simply a voluntay act to improve health or if it is related to cosmetics, weight reduction or other type of elective surgery not necessarily related to *health improvement*. <hr>
Enhancement surgery is often used to refer to cosmetic surgery like liposuccion, breast reduction or augmentation, etc.

Additionally, this is not a very hard translation and being homework the greater benefit will come from really trying to obtain the answer by ourself. This is the advice from the teacher in me.