able and willing to travel abroad to a proton facility. Commonly accepted indications for referral include chordoma and chondrosarcoma, intraocular melanoma, and solid tumours in children and adolescents who have the greatest risk for long-term sequelae. Current data do not provide sufficient evidence to recommend routine referral of patients with most head-and-neck, breast, lung, gastrointestinal tract, and pelvic cancers, including prostate cancer. It is recommended that all referrals be considered by a multidisciplinary team to select appropriate cases.