Comparative analysis of gyroscopic and robotic radiosurgery platforms for uveal melanoma treatment

To perform a comprehensive dosimetric comparison between the ZAP-X gyroscopic radiosurgery system and the CyberKnife (CK) robotic platform for the treatment of uveal melanoma (UM), with a focus on target coverage, organ at risk (OAR) sparing, plan quality metrics and treatment delivery efficiency. A total of 45 uveal melanoma patients previously treated with the CK system were retrospectively analyzed. For each patient, treatment plans were generated for both the ZAP-X and CK platforms using identical contouring datasets, shell structures, optimization parameters and dose calculation algorithms. Dosimetric parameters related to target coverage and OARs were compared, along with conformity index (CI), new conformity index (nCI), homogeneity index (HI), gradient indices (GI50% and GI25%), monitor units (MU) and estimated treatment times. Both systems achieved adequate target coverage with no significant difference in PTV D98% values. ZAP-X demonstrated significantly higher D_max, lower CI and nCI, and steeper dose gradients (GI50%, GI25%) compared to CK (p < 0.001 for all), indicating better conformity and dose fall-off. ZAP-X also delivered significantly lower doses to several OARs (p < 0.05 for all), including the optic nerves, contralateral eye, lenses, vitreous humor, lacrimal gland and brain. Although ZAP-X required more MUs per fraction, it achieved shorter treatment times. ZAP-X offers superior dose conformity, sharper dose gradients, and improved OAR sparing for uveal melanoma treatment without increasing treatment duration. While further clinical validation is required, these results support the potential of ZAP-X as a promising stereotactic radiosurgery platform for ocular tumors.