Gamma knife radiosurgery for pilocytic astrocytomas

Object. The authors report on the follow-up studies in patients treated at the Karolinska Hospital to evaluate the efficacy of gamma knife radiosurgery (GKS) for pilocytic astrocytoma. patients were children in whom GKS was performed to treat residual tumor after surgery. Most tumors were treated with a prescription dose of 10 to 12 Gy (range 9-20 Gy). The corresponding maximum dose varied between 22 and 30 Gy (range 10-50 Gy). The median clinical follow-up time was 7 years and mean clinical follow-up time 8.5 years. Median radiological follow-up time was 4.7 years and the mean radiological follow-up time was 5.9 years. Tumor control was achieved in all patients. In 85% of the cases a moderate tumor volume reduction was observed after GKS. This result occurred despite the low prescription dose administered. The radiological follow-up studies showed adverse radiation effects in 25% of patients with increasing contrast enhancement and some edema. These effects generally appeared within 7 months and resolved later. Cyst development occurred in two patients, which may have been treatment related. Conclusions. It appears that small pilocytic astrocytomas may be treated with low-prescription-dose GKS, resulting in satisfactory clinical outcomes and only minor side effects. There were a certain number of radiologically demonstrated side effects that appeared relatively early but subsequently resolved. This study should be regarded as a preliminary one because the number of patients is small and the follow-up period is short compared with the natural time course of the disease.