KEY POINTS
- This non-systematic review from the ESTRO CNS Focus Group addresses reirradiation of meningioma, ependymoma, brain metastases and pituitary neuroendocrine tumors, together with radiation necrosis management. Gliomas and glioblastoma are explicitly excluded.
- Reirradiation should not be treated as a single clinical entity. ESTRO–EORTC terminology distinguishes direct geometric overlap with the previous treatment volume from scenarios without overlap but with concern about cumulative exposure of nearby organs at risk; prior plans, spatial dose distribution, tumor volume and interval from the first course are therefore central to decision-making.
- Time alone does not reset CNS tolerance. In a recent practice survey, 53% of respondents considered 6–9 months the minimum acceptable interval for overlapping reirradiation, 25% accepted 3–6 months and 20% preferred more than one year. The optic nerves and chiasm show particularly limited recovery, with risk rising steeply at cumulative doses above approximately 55–60 Gy EQD2.
- For recurrent meningioma, commonly reported approaches include 14–18 Gy single-fraction SRS, 25–30 Gy in 5 fractions for fractionated stereotactic treatment, and 50–54 Gy in 1.8–2 Gy fractions for selected larger or skull-base recurrences. A recent meta-analysis cited by the authors estimated symptomatic radiation necrosis at approximately 8%.
- For recurrent brain metastases, repeat SRS doses around 15–18 Gy are commonly used for small lesions, while 21–24 Gy in 3 fractions or 25–30 Gy in 5 fractions are favored for larger or critically located recurrences. One salvage SRS series cited in the review reported 46.8% local control at 3 years and median overall survival of 11.7 months.
- Recurrent intracranial ependymoma remains a surgical disease when safe complete re-resection is feasible. Where reirradiation is selected, regimens such as 21 Gy in 3 fractions or 25 Gy in 5 fractions have been used, but evidence remains predominantly retrospective.
- Pituitary reirradiation requires particular caution because recurrent disease often lies close to the optic apparatus. In one small series of 15 patients, radiation-induced optic neuropathy and temporal lobe necrosis were each reported in 13.3%, illustrating how quickly cumulative-dose limitations can become clinically relevant.
- Radiation necrosis remains one of the major limiting toxicities of CNS reirradiation. Multiparametric imaging is often needed to distinguish necrosis from tumor progression; symptomatic cases may require corticosteroids, bevacizumab, surgery or laser interstitial thermal therapy, but many management data remain non-randomized and heterogeneous.
CLINICAL TAKEAWAY
CNS reirradiation is increasingly feasible, but the review reinforces that there is no universal “safe second dose.” Treatment decisions should begin with the previous plan and cumulative dose—not simply the new prescription—with particular caution around the optic apparatus, brainstem and large retreatment volumes.