Abstract
The management of localized choroidal melanoma generally involves definitive radiation therapy when globe preservation is feasible. Stereotactic radiosurgery (SRS) using the Gamma Knife system (Elekta AB, Stockholm, Sweden) or the CyberKnife system (Accuray Inc., Madison, WI, USA) is a well-established radiation modality for treating choroidal melanoma, with outcomes comparable to those of other radiation techniques. The ZAP-X Gyroscopic Radiosurgery system (ZAP Surgical Systems Inc., San Carlos, CA, USA) is a more recent platform designed for cranial SRS treatments. It may be considered a substitute for existing SRS modalities due to a similar dosimetric profile. Here, we report a case of choroidal melanoma treated using ZAP-X gyroscopic radiosurgery (GRS). A 46-year-old female presented with a medium-sized juxtapapillary choroidal melanoma in the left eye. The tumor was located nasal to the optic disc and involved the nasal half of the disc. On B-scan ultrasonography, the lesion measured 9.27 mm in its largest basal diameter and 5.55 mm in thickness. The gross tumor volume (GTV) was calculated at 0.391 cm³. A 1 mm isotropic margin was added to the GTV to account for setup errors, resulting in a planning target volume (PTV) of 0.878 cm³. A GRS treatment plan was developed using 12 isocenters to ensure adequate PTV coverage. A total of 286 non-coplanar beams were directed at the isocenter coordinates. A dose of 21 Gy in a single fraction was prescribed to the 54% isodose line at the PTV margin. Ocular akinesia was achieved using short-term general anesthesia. Treatment was delivered using the ZAP-X system, with a total treatment time of 59 minutes and 45 seconds. The delivered monitor units (MUs) totaled 23,339.47. The patient tolerated the procedure well, with no immediate post-treatment complications. Follow-up evaluations were conducted at six weeks and at three and a half months post-treatment. The patient reported no vision loss; however, fundus examination of the left eye at three and a half months revealed signs of macular edema. Regular ocular assessments and follow-up imaging are planned to monitor treatment response and evaluate long-term outcomes. This case report highlights ZAP-X as a potential alternative to established SRS modalities for the treatment of juxtapapillary choroidal melanoma. It also underscores the need for larger studies to evaluate the efficacy and safety of ZAP-X in the management of choroidal melanoma.