ZAP-X Stereotactic Radiosurgery: The Initial Experience Involving 200 Patients

The ZAP-X (ZAP Surgical Systems, Inc., San Carlos, CA) is the newest dedicated cranial stereotactic radiosurgery (SRS) platform. A prospective study was conducted between October 2023 and January 2025 involving 200 patients with 374 intracranial targets treated using ZAP-X. The study aimed to assess the feasibility of the ZAP-X workflow, as well as its safety, clinical and dosimetric performance, and patient satisfaction. The study cohort included various central nervous system pathologies, including 106 brain metastases (BM), 42 meningiomas (MA), 18 trigeminal neuralgias (TN), 11 acoustic neuromas (AN), nine recurrent glioblastomas (RGBM), seven pituitary adenomas (PA), three spinal tumors (ST), three arteriovenous malformations (AVM), and one cavernous hemangioma of the pons (HM). The average number of patients treated per month was 13 ± 2, and the average number of treatments per month was 35 ± 9. The maximum number of patients treated in a day was five. The average gamma passing rate was 98.5 ± 1.7% (91.2 - 100%) at a 10% low-dose threshold, 2% dose difference, and 1 mm distance-to-agreement. The average conformity index (CI), Paddick conformity index (PCI), gradient index (GI), homogeneity Index (HI), and gradient measure across all patients were 1.3 ± 0.3, 0.77 ± 0.11, 3.3 ± 0.8, 1.5 ± 0.3, and 0.38 ± 0.16 cm, respectively. The largest tumor volume treated was 29.29 cm^3, and the highest number of targets treated in a single course was 10. Average treatment time was 50 ± 20 minutes, with setup time being the most significant predictor (adjusted r² = 0.972). The Efficast head and shoulder mask significantly improved patient comfort and reduced alignment errors compared to head-only masks. Patient satisfaction was high across all measured domains, with average scores ranging from 4.7 to 5.0 on a 5-point scale. The most common treatment side effects were fatigue and headache. This initial experience represents the largest single institution series to date and supports the ZAP-X as a promising alternative to conventional SRS platforms such as Gamma Knife (GK) and CyberKnife (CK). Continued research and multi-institutional studies are warranted to further validate these findings and assess long-term outcomes.