Table 1.

Comparison between photon, proton, and carbon-based radiotherapy.

	Carbon ions	Protons	Photons
Year of first treatment	1994a	1954	Late 1800s and early 1900sb
Number of sites treating (as of June 2019)	12c	83d	Routine
Bragg-Peak	Present	Present	Absent
Estimated RBEa	2.5–5.0	1.1	1.0
Relative LET	Highest	High	Low
Relative risk of secondary malignancye,f	Low	Low	High

RBE, relative biologic effectiveness; LET, linear energy transfer.

^aMohamad et al. (6).

^bGianfaldoni et al. (7).

^cLazar et al. (3).

^dParticle Therapy Co-Operative Group (4).

^eEley et al. (8).

^fMohamad et al. (9).