Background: Stereotactic radiosurgery has become a widespread treatment alternative especially in benign central nervous system lesions. So far, only a few cases of photon beam radiosurgery-induced oncogenesis have been
reported.
Case report: The authors report a patient who underwent Bragg proton beam radiosurgery through two bi-occipital portals for a surgically inaccessible left-sided occipital high-flow arteriovenous malformation (AVM). 19 years
after irradiation, the patient developed a mild left-sided hemiparesis together with a progressive change of his mental status. Magnetic resonance imaging (MRI) demonstrated a predominantely cystic fronto-polar lesion on
the right side. Neuropathological investigation after microsurgical resection revealed a glioblastoma multiforme (WHO IV°). Based on a thorough review of the literature, this constellation had not been described previously.
Conclusions: Despite the common use of stereotactic radiosurgery in any application, the risk of delayed cerebral neoplasia reported to occur after fractionated irradiation still remains to be clarified. In the presented case, the
causal relationship between proton beam radiosurgery and formation of a malignant brain tumor is discussed.

Keywords: stereotactic radiosurgery, proton beam, radiation-induced tumor, glioblastoma multiforme, cerebral arteriovenous malformation