To cite package 'survival' in publications use:

Terry Therneau (2012). A Package for Survival Analysis in S. R package version 2.36-14.

Corresponding BibTeX entry:

  @Manual{,
    title = {A Package for Survival Analysis in S},
    author = {Terry Therneau},
    year = {2012},
    note = {R package version 2.36-14},
  }