[Koha] opac-basket.tt

I have a question: How I can do to add a new field in koha cart? opac-basket.tt I need to print my cart with the field 773$t and other fields. I try to add this: BIBLIO_RESULT.marcxml... but this adds all the marc detail. I only need 773$t and 773$g Any idea... thank you, and sorry my english.