Initial Experience with Gyroscopic Radiosurgery for Brain Metastases: A Case Series

Introduction: The ZAP-X is the newest cranial stereotactic radiosurgery (SRS) platform. There are few reports describing its use or outcomes for brain metastases (BM). In this study, dosimetric parameters and initial clinical outcomes are analyzed for ZAP-X BM SRS.

Methods: Twenty-seven patients were treated with ZAP-X BM SRS. The average prescription dose was 24±4 Gy (range: 18–30 Gy), the average prescription isodose line was 70±10% (range: 53–84%), the average number of targets was 2±2 (range: 1–10), the average total target volume was 8±9 cm3 (range: 0.21–30.84 cm3), the average number of isocenters was 8±4 (range: 1–18), the average number of beams was 180±70 (range: 42–349), and the average number of fractions was 2.6±1.6 (range: 1–5). Primary tumors included pulmonary (63%), breast (7%), skin (7%), head and neck (7%), gastrointestinal (4%), uterine (4%), colon (4%), and renal (4%). Patient clinical outcome was assessed using the Response Assessment in Neuro-Oncology Brain Metastases (RANO-BM) criteria. Follow-up was scheduled 3, 6, 9, and 12-months post-treatment.

Results: All patients underwent successful treatment. The average conformity index was 1.23±0.17 (range: 1.041–1.758), the average gradient index was 3.3±0.6 (range: 2.467–4.587), and the average treatment time was 51±16 minutes (range: 12–96 minutes). Median follow-up was 151 days (IQR: 98.5–294.5 days). Of the twenty-seven patients, 10 (37.0%) were classified as partial response, 9 (33.3%) as stable, and 8 (29.6%) as progressive disease (local tumor control=70%). Median ECOG status was 1 (IQR: 1–2) at baseline, 2 (IQR: 1–2) at 3 months, 1 (IQR: 1–2) at 6 months, and 1 (IQR: 1–2) at 12 months.

Conclusion : The ZAP-X platform demonstrates promising initial outcomes, with favorable dosimetric performance and local control rates, reinforcing its potential as a standard tool in SRS for brain metastases.