Inclusion Criteria:  Histologically diagnosed with primary or recurrent chordoma or chondrosarcoma in the axial skeleton (clivus, spine and sacrum) Accepted for standard proton beam therapy  Exclusion Criteria:  Diagnosis other than chordoma or chondrosarcoma is made. Patient refuses (parts) of the standard treatment protocol. Patient refuses MRI due to claustrophobia. Patient not suitable for MRI due to the presence of MRI incompatible implants. Incapacitated patients. Patient doesn't allow coded data to be used for analysis. Patient is under 50 years of age. Lesion size less than 1cm. Patients with WHO 3 and higher.