Executive summary

This review presented the roadmap for proton therapy development, which included further research in the advanced dose shaping capabilities of proton therapy cause susceptibility to uncertainties; the high degrees of freedom in dose delivery offer room for further improvements; the limited experience and understanding of optimizing pencil beam scanning; and the biological effects differ from photon radiation.

In addition to these challenges and opportunities currently being investigated, there is an economic aspect because proton therapy treatments are, on average, still more expensive compared to conventional photon-based treatment options. This roadmap highlights the current state and future direction in proton therapy categorized into four different themes, "improving efficiency", "improving planning and delivery", "improving imaging", and "improving patient selection".