A former pain doctor who worked in Santa Rosa has been sentenced to two-and-a-half-years in prison. Seventy-five-year-old Thomas Keller was sentenced Thursday and has until September 8th to turn himself in. In November, Keller was convicted on four counts of unlawful distribution of controlled substances. Prosecutors said he distributed the drugs without a legitimate medical need and did so outside the scope of his professional practice. Keller ran a pain management practice in Santa Rosa.