Imaging for radiosurgery treatment

Imaging for target localization and alignment is an important component of modern radiation oncology. Nowhere is this more critical than in stereotactic radiosurgery, for which the CyberKnife system is employed for central nervous system applications at our institution. The CyberKnife system's accuracy allows for treatment of the target without additional added margin for positioning variability. This confidence allows the clinician to deliver very high doses to the region of interest, while maximally sparing normal tissues from unnecessary and potentially damaging radiation dosage, allowing for potentially less toxic and more effective than its predecessors. In order to deliver stereotactic treatment, imaging for target localization and distinguishing the target of interest from surrounding normal tissue is of utmost importance. Plans for CyberKnife treatment are determined based on a fusion of magnetic resonance imaging (MRI) and planning computed tomography (CT) images. MRI series are registered and fused to CT images, and verification that the patient's rigid boney anatomy aligns with the planning CT image is achieved via kV imaging and compensation for small movements with the machine's robotic arm. In this chapter, the authors describe these imaging modalities in greater detail, focusing primarily on MRI techniques in CyberKnife treatment planning and the clinical contexts in which they are employed.