An exact method for minimizing the total treatment time in intensity-modulated radiotherapy

In this paper, we solve a combinatorial optimization problem that arises from the treatment planning of a type of radiotherapy where intensity is modulated by multileaf collimators in a step-and-shoot manner. In Ernst et al. [INFORMS Journal on Computing 21:4 (2009) 562–574], we proposed an exact method for minimizing the number of multileaf collimator apertures needed for a treatment. Our method outperformed the fastest algorithms available at the time. We refer to our method as the CPI method. We now attempt to minimize the total treatment time by modifying our CPI method. This modification involves non-trivial work, as some of the search space elimination schemes used in the CPI method cannot be applied in here. In our numerical experiments, we again compare our new method with the fastest algorithms currently available. There has been significant recent research in this area hence we compare our method with those published in Wake et al. [Computers and Operations Research 36 (2009) 795–810], Taskin et al. [Operations Research 58:3 (2010) 674–690] and Cambazard et al. [CPAIRO (2010) 1–16]. The numerical comparisons indicate that our method generally outperformed the first two, while being competitive with the third.