To cite aftgee in publications use:

  Sy Han Chiou, Sangwook Kang, Jun Yan (2014). Fitting Accelerated
  Failure Time Models in Routine Survival Analysis with R Package
  aftgee. Journal of Statistical Software, 61(11), 1-23. URL
  https://doi.org/10.18637/jss.v061.i11

A BibTeX entry for LaTeX users is

  @Article{,
    title = {Fitting Accelerated Failure Time Models in Routine Survival Analysis with {R} Package {aftgee}},
    author = {Sy Han Chiou and Sangwook Kang and Jun Yan},
    journal = {Journal of Statistical Software},
    year = {2014},
    volume = {61},
    number = {11},
    pages = {1--23},
    url = {https://doi.org/10.18637/jss.v061.i11},
  }