Stereotactic Ablative Radiotherapy for Delayed Retrobulbar Metastasis of Renal Cell Carcinoma: Therapeutic Outcomes and Practical Insights

We present a rare case of delayed retrobulbar and adrenal metastases from renal cell carcinoma (RCC), diagnosed 5.5 years after radical nephrectomy. The patient exhibited symptomatic orbital involvement, with imaging revealing a hypervascular retrobulbar mass and an incidental right adrenal lesion, indicative of an oligometastatic state. Owing to the patient's refusal of surgical resection, stereotactic ablative radiotherapy (SABR) was delivered to the retrobulbar lesion at a total dose of 40 Gy in five fractions, concurrently with immune checkpoint inhibitor therapy. Treatment planning prioritized sparing adjacent critical structures, including the optic chiasm and brainstem. Follow-up over 4 years demonstrated sustained radiologic stability and volume reduction in both metastatic lesions without evidence of progression. This case underscores the potential efficacy of SABR in achieving durable local control of RCC metastases, particularly in anatomically constrained regions where surgery is unfeasible. Moreover, it highlights the value of a multidisciplinary, multimodal treatment approach incorporating advanced radiotherapy techniques and systemic immunotherapy. Lastly, it reinforces the importance of prolonged surveillance in RCC survivors due to the potential for late metastatic recurrence at uncommon sites.