Role of Neuroimaging in Brain Radiosurgery

Radiosurgery is a therapeutic technique to deliver high dose radiation to the target. It induces radiobiological responses of lesions while minimizing radiation effect to the surrounding area. Gamma knife is one of the representative devices for stereotactic radiosurgery, which is exclusively designed for treatment of cerebral disorders. Gamma knife was developed as the first radiosurgical device in 1967. Professor Lars Leksell at the Karolinska Institute in Sweden developed a stereotactic frame for functional neurosurgery in early 1950s and combined the technique of frame fixation with focused irradiation. The primary role of gamma knife radiosurgery is to control small well-demarcated lesions such as metastatic brain tumors, meningiomas, schwannomas, and pituitary adenomas while preserving function of surrounding brain tissue. It has been used as a primary treatment or in combination with surgery, and some applications have been accepted as standard treatment. Treatment of cerebral arteriovenous malformations has also been drastically changed after emergence of this technology. Arteriovenous malformation in deep locations such as the basal ganglia, thalamus and the brainstem came to be safely treated by radiosurgery. Stereotactic radiosurgery is also employed in the control of functional disorders such as mesial temporal epilepsy and trigeminal neuralgia. As such, gamma knife has been widely accepted in clinical practice in the field of neurosurgery (Koga et al., 2010). On the other hand, the risk of radiation-induced adverse events is not negligible and puts limitations to this technology. Accurate target definition is one of the most important factors to reduce complications because it can reduce unwanted radiation to surrounding normal tissue. The target of radiosurgery is primarily visualized by radiological studies such as angiography, computed tomography and magnetic resonance imaging. Owing to this, the accuracy of treatment largely depends on neuroimaging technology. After introduction of gamma knife, technology of neuroimaging has also been drastically changed as an example of magnetic resonance imaging. Not only neuroimaging itself, but also software to utilize different kinds of imaging modalities for treatment planning of radiosurgery has been developed in the past decades. During almost a half century since treatment of gamma knife radiosurgery was applied for the first patient, technology of radiosurgery has progressed in line with the advances in neuroimaging technology. In this chapter, we discuss technological advances in neuroimaging and consider i) how these have driven more sophisticated radiosurgical treatments and ii) the impact on post radiosurgical outcomes.