Gamma knife robotic microradiosurgery for benign skull base meningiomas: Tumor shrinkage may depend on the amount of radiation energy delivered per lesion volume (Unit Energy)

Background/Aims: The objective of the present study was the evaluation of the effectiveness of robotic microradiosurgery of skull base meningiomas using Leksell Gamma Knife model C with an automatic positioning system. Methods: The results of the management of 66 tumors were analyzed retrospectively. Their volume varied from 0.3 to 50.6 cm³ (mean = 6.6). The treatment plan was based on the use of multiple small isocenters compactly positioned within the border of the lesion with resultant improved homogeneity of high-dose distribution, increased average dose within the target and sharp dose fall outside the treated volume. The marginal dose varied from 10 to 14 Gy (mean = 12). The length of follow-up ranged from 26 to 80 months (mean = 46). Results: The overall tumor growth control was 99%. Reduction of the mass volume was marked in 54 patients (82%), and in 15 of them it constituted ≥50%. In other 11 cases (17%) stabilization of the lesion growth was noted. The shrinkage rate significantly correlated with amount of radiation energy delivered per tumor volume, designated as unit energy (p = 0.007). One meningioma (1%) regrew 3.5 years after radiosurgery. The treatment-related morbidity was limited to transient abducens nerve palsy in 1 patient (1%). Conclusion: Application of the concept of Gamma Knife robotic microradiosurgery for the management of skull base meningiomas may change the paradigm of their treatment from stabilization of growth to reduction of the volume of the neoplasm. The tumor shrinkage rate may depend on the amount of radiation energy delivered per lesion volume (unit energy).