Background: Dose painting is a concept that may increase the tumor control probability (TCP). In particle therapy of hypoxic tumors, it may also be beneficial to redistribute the linear energy transfer (LET) so that the oxygen effect is minimized; so-called LET painting. The purpose of the present study was to use TCP estimates for comparing dose and LET painting of hypoxic tumors.
Material and methods: Protons, lithium ions and carbon ions were considered. Tumor images tentatively depicting hypoxia were used as input. Optimal dose prescription maps were obtained by optimizing TCP under dose and/or LET redistribution. TCPs were compared to those resulting from conventional particle therapy with no dose or LET painting. The therapeutic gain at a given iso-effect was calculated. Treatment adaptation during therapy in response to changes in the spatial hypoxia distribution was also considered.
Results: Both dose and LET painting gave higher TCPs compared to conventional particle therapy, irrespective of particle type. The therapeutic gain from LET painting, dose painting and combined dose+ LET painting was 1.09/1.43/1.45, 1.24/1.32/1.37 and 1.16/1.23/1.28 for protons, lithium ions and carbon ions, respectively. The importance of treatment adaptation was less pronounced for particles heavier than protons.
Conclusion: Dose painting results in higher TCP than LET painting, in particular for protons. For heavier ions, LET painting may also give an enhanced tumor effect compared to conventional particle therapy. Combined dose+ LET painting may only give a marginally increased effect compared to dose painting only. Adaptive carbon ion dose painting seems to be of less importance.