  In the past decades mathematical optimization has found its way into
radiation therapy and has made profound practice changing impact. Today,
virtually all advanced treatment delivery methods, such as IMRT, VMAT,
tomotherapy, LDR/HDR brachytherapy, proton therapy, are based on some form of
optimization approach that changes the treatment variables (beam intensities,
multileaf collimator shapes, beam angles, dwell times and seed or source
positions) in the planning computer using an optimization algorithm, until the
best value of the treatment (planning) objective has been found. It is fair to
say though that a truly optimal radiation treatment plan remains elusive. The
reasons for that include difficulties in defining meaningful planning
objectives and constraints in mathematical terms, various uncertainties in the
planning and delivery process, and the inability of optimization algorithms to
find the true optimum. Radiation therapy optimization therefore remains an
active field of research.
