Fig. 1

Trial summary of IMPROVE CODEL/NOA-18. RT: For CNS WHO grade 3 oligodendroglioma: Radiotherapy is performed as 33 fractions of 1.8 Gy for a total dose of 59.4 Gy. One fraction is given daily five days per week for about 6 to 7 weeks. For CNS WHO grade 2 oligodendroglioma, radiotherapy is performed as 28 fractions of 1.8 Gy for a total dose of 50.4/54 Gy for over approximately 5–6 weeks. Tx Break: Rest period is 4 weeks long (± 2 weeks) total. PCV: PCV chemotherapy, cycles are about 6 weeks long each. Day 1: CCNU 110 mg/m² orally (capped at 200 mg); Days 8 and 29: vincristine 1.4 mg/m² i.v. (capped at 2 mg); Days 8 to 21: procarbazine 60 mg/m² orally (capped at 100 mg). CETEG: CCNU/temozolomide chemotherapy cycles are 6 weeks long. Day 1: CCNU 100 mg/m² orally (capped at 200 mg); Days 2–6: Temozolomide 100 mg/m² (cycle 1) with dose escalation in 50 mg/m² steps according to toxicity in subsequent cycles. ⁺Therapy at progression is as suggested at the time of the protocol preparation. It is reasonable that patients without prior radiotherapy will undergo radiotherapy; it is also very likely that PCV will be used as adjunct chemotherapy if bone marrow reserve allows and if there are no safety concerns from the initial CETEG treatment. The treatment at progression in the standard arm is less predictable; there may be an option for second radiotherapy or even reuse of the full radiochemotherapy regimen as it had been given at diagnosis. The trial will therefore continue to assess any endpoint-relevant scans and scales and also list the secondary treatments, but not attempt a full registration of the treatment, which is considered standard and not driven by trial requirements