Nikoghosyan et al. BMC Cancer 2010, 10:607 http://www.biomedcentral.com/1471-2407/10/607 Page 3 of 9 Figure 1 Typical dose distribution of carbon ion therapy by clivus chordoma patient (axial view and dose legend; red line defines CTV; both eyes, optic nerves and brain steam are also shown). skull base. Study patients are selected according to the inclusion criteria of the study protocol. After careful review of the patient reports and results of the addi- tional examinations eligibility of a patient is determined. Patients matching the eligibility criteria and willing to participate are registered. These patients are subse- quently randomised to one of the two treatment arms (arm A: carbon ion therapy, arm B: proton therapy). Arm A: carbon ion therapy with a total target dose of 63 Gy E ± 5% to the PTV1 (s. also target definition). The PTV2 will receive a total carbon ion dose of 45 Gy E. The patients entered in Arm B will receive proton therapy with the same target definition concept. The total proton dose will be 72 Gy E ± 5%. The PTV2 will receive a total dose of 50 to 56 Gy E in conventional fractionation (s. also dose prescription). Accrual period for the trial will be approximately 5 years. Our study design contains interim analysis after 50% of the predicted events have occurred.