Table 1.

The list of prerequisites for proton systems in 10 years that can be retrofitted to existing facilities

#	Feature	Existing facilities	New facilities —paradigm bound	New facilities to be designed
1	Proton arc therapy	?	X	X
2	Rapid beam delivery enabling FLASH therapy	?	?	X
3	Proton beam-based Image guidance—in-vivo range verification and proton beam imaging	X	X	X
4	Online adaptive therapy—on the fly. Bring the beam to the patient	?	X	X
5	Beam control based on the patient’s respiration cycle—full 4D beam delivery	X	X	X
6	Fast trimming apertures		X	X
7	Beam focusing conditions —variable spot size	?	X	X
8	System self-diagnostics and self-calibration—automatic warm-up and checking overnight	X	X	X

4D, four-dimensional.

Aquestion mark indicates that it might already be possible to upgrade anexisting facility, but it might not be cost effective or feasible.