Zap-X Radiosurgery System: Initial Clinical Experience in a Recurrent Gamma Knife Case Series

The ZAP-X® Gyroscopic Radiosurgery System (ZAP Surgical Systems, Inc., San Carlos, CA, USA) is expected to be a highly accurate next-generation treatment system that enables gyro-stereotactic irradiation of intracranial lesions. In this study, we report the initial treatment course using ZAP-X for intracranial lesions that recurred after Gamma Knife (GK) treatment.

Patients with intracranial tumors treated with ZAP-X from April to August 2023 who relapsed after GK therapy were eligible for participating in this study. The primary endpoint was the progression control rate at six months; the secondary endpoints were the rate of target lesion reduction, treatment effect by tumor doubling time (TDT) before ZAP-X intervention, and adverse events.

Six lesions were evaluated in six patients (two meningiomas, one solitary fibrous tumor, one auditory neuroma, one glomus tumor, and one metastatic tumor). The mean follow-up period was 10.6 months after treatment. The mean lesion volume was 5.3 cm³; the mean TDT was 241 days. The six-month progression control rate was 100%, with two partial responses and four stable diseases at the last evaluation. Adverse events were limited to only imaging changes in one patient (16.6%), indicating a significant correlation between ZAP-X pre-intervention TDT and post-intervention reduction rate.

The initial results of ZAP-X treatment in patients with recurrent disease following GK are reported for the first time. ZAP-X demonstrated potent anti-tumor efficacy and adequate tolerability and should be considered a new treatment option for relapsed refractory patients. Future studies should increase the number of cases and follow-up periods to further evaluate treatment outcomes and adverse events.