Gamma Knife surgery of large meningiomas: early response to treatment

Gamma Knife treatment is traditionally limited to tumours with a diameter not exceeding 3-3.5 cm. The current paper presents 97 patients with meningiomas with a minimum volume of 10 cm(3), treated with a prescription dose of 12 Gy (or sometimes less to protect neighbouring structures). The post-treatment assessment of these patients, the early response to treatment and the complications of treatment are presented. There were 97 patients, 70 females and 27 males. The mean age was 48.1 years (range 20.4-87.2 years). The mean follow-up was 54 months (range 25-86 months). All tumours had a volume of 10 cm(3) or more. The mean volume was 15.9 cm(3) (range 10.0-43.2 cm(3)). Post-treatment follow-up used quantitative and qualitative assessments, which are described. No tumour continued to grow. Twenty-seven were smaller and 72 unchanged in volume. Three patients suffered adverse radiation effects (defined as a new post-treatment oedema detected on the magnetic resonance image with or without contrast leakage). In one case this was silent. In two cases the clinical and radiological effects were temporary and resolved completely. It is suggested on the basis of this material that the dosimetry used here permits the safe Gamma Knife treatment of larger meningiomas within the range reported. The early radiological response is encouraging, but further follow-up is needed to check long term tumour control. A qualitative method of tumour volume assessment is presented. It seems to be a simpler and more reliable way of assessing tumour volume changes than other methods currently in routine use.