To cite riskRegression in publications use:

Gerds TA, Kattan MW (2021). Medical Risk Prediction Models: With Ties to Machine Learning (1st ed.). Chapman and Hall/CRC. https://doi.org/10.1201/9781138384484.

Corresponding BibTeX entry:

  @Book{,
    title = {Medical Risk Prediction Models: With Ties to Machine
      Learning (1st ed.)},
    author = {Thomas A. Gerds and Michael W. Kattan},
    publisher = {Chapman and Hall/CRC},
    year = {2021},
    url = {https://doi.org/10.1201/9781138384484},
  }