Inclusion Criteria:  Patients must be 18 to 65 years old at the day of consenting IDH-mutated astrocytoma grade II or III, or oligodendroglioma grade II or III according to WHO 2016 Indication for radiotherapy WHO/ECOG performance status 0-2 Available MRI not older than 2 months at study inclusion, preferably including volumetric FLAIR-imaging No significant contrast enhancing tumor at the time of randomization Ability and willingness to travel to The Skandion Clinic for proton therapy if randomized to the proton therapy arm Women of child-bearing potential (WOCBP) must agree to use an effective method of contraception during radiotherapy, chemotherapy and 1 year after completion of chemotherapy. Pregnancy is not an ineligibility criterium if radiotherapy is indicated and cannot be postponed Ability to understand the information about the study and included treatment and give a written informed consent  Signed informed consent  Exclusion Criteria:  Prior treatment (except surgery) for diffuse glioma Concomitant or previous malignancies. Exceptions are adequately treated basal cell carcinoma or squamous cell carcinoma of the skin, or in situ carcinoma of the cervix uteri with a follow-up time of at least 3 years, or other previous malignancy with a disease-free interval of at least 5 years More than 2 months from randomization to start radiotherapy Known CDKN2A/B homozygous deletion Presence of any medical, psychological, familial, sociological, or geographical characteristic that might impair patient compliance for study protocol procedures including follow-up