Pediatric CNS relapse of neuroblastoma treated with upright proton craniospinal irradiation.

Craniospinal irradiation (CSI) is a technically demanding treatment in pediatric oncology, especially for young children, who often require daily anesthesia. Although proton therapy offers dosimetric advantages over photons by eliminating exit dose and reducing exposure to healthy tissues, its global availability is limited due to the cost and complexity of gantry-based systems. Recently, gantry-less proton therapy with upright positioning has recently emerged as a compact, cost-efficient alternative, integrating robotic positioning and vertical CT-based image guidance. This study reports the first pediatric case of upright proton CSI delivered under intravenous monitored anesthesia care (MAC) using such a system. A four-year-old male patient with relapsed neuroblastoma in the central nervous system received CSI at a dose of 18.0 Gy(RBE) in 12 fractions, along with a simultaneous integrated boost (SIB) of 21.6 Gy(RBE) to the resection cavity. This was followed by a sequential boost to the resection cavity in five fractions, for a total dose of 30.6 Gy(RBE). The treatment was performed in the seated position with customized immobilization, upright volumetric CT verification, and reproducible daily setup. MAC achieved without intubation, allowing continuous airway access. The patient completed the treatment regimen without interruption, did not experience any grade 2 or higher acute toxicities, and demonstrated adequate tolerance of daily anesthesia. This case demonstrates the clinical feasibility of upright proton CSI under MAC and provides proof of concept for the broader adoption of gantry-less proton therapy in complicated cases.