  Dosimetry with ionization chambers in clinical ion beams for radiation
therapy requires correction for recombination effects. However, common
radiation protocols discriminate between initial and general recombination and
provide no universal correction method for the presence of both recombination
types in ion beams of charged particles heavier than protons. Here, we present
the open source code IonTracks, where the combined initial and general
recombination effects in principle can be predicted for any ion beam with
arbitrary particle-energy spectrum and temporal structure. IonTracks uses track
structure theory to distribute the charge carriers in ion tracks. The charge
carrier movements are governed by a pair of coupled differential equations,
based on fundamental physical properties as charge carrier drift, diffusion,
and recombination, which are solved numerically while the initial and general
charge carrier recombination is computed.
  The algorithm is numerically stable and in accordance with experimentally
validated theories for initial recombination in heavy ion tracks and general
recombination in a proton beam.
  IonTracks is validated against the Jaff\'e's and Boag's theory of
recombination in pulsed beams of multiple ion species. IonTracks is able to
calculate the correction factor for initial and general recombination losses in
parallel-plate ionization chambers. Even if only few experimental data on
recombination effects in ionization chambers are available today, the universal
concept of IonTracks is not limited to the ions investigated here. Future
experimental investigations of recombination in pulsed and possibly also
continuous ion beams may be conducted with IonTracks, which ultimately may lead
to a more precise prediction of recombination factors in complex radiation
fields.
