context: Following the success of the 2005 series produced by Russell T Davies, the BBC commissioned Davies to produce a 13-part spin-off series titled Torchwood (an anagram of "Doctor Who"), set in modern-day Cardiff and investigating alien activities and crime. The series debuted on BBC Three on 22 October 2006. John Barrowman reprised his role of Jack Harkness from the 2005 series of Doctor Who. Two other actresses who appeared in Doctor Who also star in the series; Eve Myles as Gwen Cooper, who also played the similarly named servant girl Gwyneth in the 2005 Doctor Who episode "The Unquiet Dead", and Naoko Mori who reprised her role as Toshiko Sato first seen in "Aliens of London". A second series of Torchwood aired in 2008; for three episodes, the cast was joined by Freema Agyeman reprising her Doctor Who role of Martha Jones. A third series was broadcast from 6 to 10 July 2009, and consisted of a single five-part story called Children of Earth which was set largely in London. A fourth series, Torchwood: Miracle Day jointly produced by BBC Wales, BBC Worldwide and the American entertainment company Starz debuted in 2011. The series was predominantly set in the United States, though Wales remained part of the show's setting.
question: What Doctor Who spin-off series was commissioned by the BBC?
answers: Torchwood Torchwood Torchwood