Dosimetric Comparison of Contemporary Stereotactic Radiotherapy Platforms for Brain Metastases: Towards Personalized...

Stereotactic radiosurgery and radiotherapy (SRS/SRT) for brain metastases is a rapidly evolving field, driven by continuous refinement of dosimetric strategies and technological advances in treatment platforms. This narrative review synthesizes current evidence on the dosimetric characteristics of major SRS/SRT platforms-Gamma Knife, CyberKnife, ZAP-X, linear accelerators, helical tomotherapy, and proton therapy-and evaluates their comparative strengths, limitations, and optimal clinical applications. We identify distinct dosimetric trade-offs among platforms with respect to dose conformity, gradient fall-off, normal tissue sparing, and treatment efficiency. Gamma Knife remains a dosimetric benchmark for dose gradient steepness, particularly for small targets (e.g., <1 cm in diameter). CyberKnife offers high conformity and may benefit lesions adjacent to critical organs, although treatment efficiency diminishes with increasing numbers of metastases. The novel, self-shielded ZAP-X system delivers a dose gradient comparable to that of Gamma Knife and achieves favorable sparing of normal brain tissue at intermediate-to-high dose levels. Linear accelerator-based techniques-especially single-isocenter non-coplanar volumetric modulated arc therapy and dynamic conformal arc therapy-are widely adopted for multiple brain metastases owing to their high delivery efficiency and continually improving plan quality. Helical tomotherapy provides reliable plan deliverability, whereas proton therapy offers a theoretical advantage in reducing low-dose exposure to the whole brain and sparing adjacent organs at risk, owing to the Bragg peak. The available evidence indicates that no single platform is universally optimal, and dosimetric differences should be interpreted with caution given the absence of prospective comparative clinical outcome data. Treatment platform selection should therefore be individualized, integrating disease characteristics (e.g., number, volume, location, and geometry of targets), institutional resources, and established clinical priorities. Future integration of advanced technologies-including FLASH radiotherapy and artificial intelligence-may further personalize the management of brain metastases.