Evaluation of radiological recurrence patterns following gamma knife radiosurgery for solitary meningioma previously treated via cranial surgery

The use of gamma knife radiosurgery (GKS) for meningiomas after cranial surgery has been extensively evaluated; however, studies on tumor progression, including recurrence out of the margin dose line, are scarce. Hence, we aimed to evaluate the meningioma recurrence after GKS within and out of the margin dose. We included 37 consecutive patients with World Health Organization (WHO) grade 1 meningiomas who were treated with GKS following cranial surgery. Radiologically indicated recurrences were classified into three patterns by their relationship to the margin dose and tumor. The median follow-up was 58.9 months; 2 (5.4%) patients died. Only 2 (5.4%) patients did not keep active daily lives because of tumor progression. Cumulative local control at 5 years was 85.2%. Local recurrence and recurrence out of the margin dose occurred in 5 (13.5%) and 13 (35.1%) patients, respectively. A larger preoperative maximum diameter was a risk factor for local recurrence (hazard ratio [HR]: 2.118; P = 0.033), adjacent progression (HR: 1.633; P = 0.015), and remote progression (HR: 2.016; P = 0.003). Symptomatic adverse radiation effects occurred in 1 patient. Salvage GKS and cranial surgery were performed in 9 (24.3%) and 8 (21.6%) patients, respectively. Progression to WHO grade 2–3 occurred in 5 (13.5%) patients. A larger preoperative maximum diameter was a risk factor for progression of WHO grade (HR: 2.016, P = 0.033). Progression out of the margin dose was associated with a larger preoperative tumor size.