Adult medulloblastoma is a rare entity with a predilection for the development of radiation-induced malignant glioma (RIMG). Management of RIMG in the setting of prior craniospinal irradiation is a challenging scenario.

We report a case of a 51-year-old male with short-interval development of multicentric malignant glioma with MET mutation who previously underwent craniospinal radiation for adult medulloblastoma. Due to radiographic findings, linear accelerator (LINAC)-based fractionated stereotactic/IMRT was delivered to the right temporal lesion alongside systemic therapy. The patient had interval development of an IDH wildtype, high-grade left cerebellar glioma and underwent surgical resection and subsequent gamma knife stereotactic radiosurgery (GKRS) to the cavity.

GKRS targeting the surgical cavity was delivered with a fractionated regimen of 27 Gy in 3 fractions to the margin. One year after completion of GKRS, the patient had not developed any symptomatic radiation necrosis or neuroimaging changes reflective of treatment toxicity. In this patient, GKRS to minimise the integral dose exposure of normal tissues surrounding the target volume proved to be particularly advantageous in the setting of prior craniospinal irradiation.

RIMG poses significant challenges for radiation oncologists, particularly in the reirradiation setting. Decision-making involving multidisciplinary input balanced the necessity of dose escalation achieved by GKRS, while minimising the cumulative dose in the setting of prior craniospinal irradiation.