Radiological Parameters for Gamma Knife Radiosurgery.

Accurate lesion targeting is the essence of stereotactic radiosurgery. With the currently available imaging modalities, scanning has become quick and robust providing a high degree of spatial resolution resulting in optimal contrast between normal and abnormal tissues. Magnetic resonance imaging (MRI) forms the backbone of Leksell radiosurgery. It produces images with excellent soft tissue details highlighting the target and surrounding "at-risk" structures conspicuously. However, one must be aware of the MRI distortions that may arise during treatment. Computed tomography (CT) has quick acquisition times giving excellent bony information but inferior soft tissue details. To avail benefits of both these modalities and overcome their individual fallacies and shortcomings, they are often co-registered/fused for stereotactic guidance. Vascular lesions like an arteriovenous malformation (AVM) are best planned with cerebral digital subtraction angiography (DSA) in conjunction with MRI. In specific cases, specialized imaging methods like magnetic resonance (MR) spectroscopy, positron emission tomography (PET), magneto-encephalography (MEG), etc., may be added to the treatment planning for stereotactic radiosurgery (SRS).