Basic Principles

• The first step in a planning radiosurgical procedure is to obtain adequate high quality stereotactic images.
  
• The fiducial box is placed on the base ring of the stereotactic frame, then the head is secured in a special holder for the time of imaging.
  
• Focus images on the region of interest (no need to image the whole head, except for brain metastases).
  
  
  
  • Some technologies require whole imaging to calculate beam attenuation.
  
  
• Verify that fiducials are adequately seen in each image series (required to later define stereotactic space in the planning computer).

Magnetic Resonance Imaging

• Imaging modality of choice for most cases because of optimal contrast definition between normal and abnormal tissues, and high spatial resolution
  
• May be subject to artifact causing distortion of stereotactic coordinates, therefore the fiducials must be measured and compared between each side to ensure image accuracy
  
• Volumetric acquisition of images is optimal (do not skip any image signal between slices)
  
• Suggested imaging sequences
  
  
  
  • Acoustic neuromas
    
    
    
    • One- to 1.5-mm thick contrast-enhanced spoiled-gradient recalled acquisition in steady state (SPGR) images
      
    • One-millimeter thick T2-weighted imaging (to help define the intracanalicular portion and inner ear anatomy)
    
    
  • Meningiomas
    
    
    
    • One- to 1.5-mm thick contrast-enhanced SPGR images
    
    
  • Pituitary adenomas
    
    
    
    • One- to 1.5-mm thick contrast-enhanced SPGR images (with or without fat suppression)
    
    
  • Arteriovenous malformations
    
    
    
    • One- to 2-mm thick contrast-enhanced SPGR images
    
    
  • Brain metastases
    
    
    
    • Two-millimeter thick SPGR sequence with double-dose contrast covering the whole head
    
    
  • Trigeminal neuralgia
    
    
    
    • One-millimeter thick contrast-enhanced SPGR sequence
      
    • T2-weighted images may assist nerve definition (especially in cases of previous surgical management)

• Generally used only if there is a contraindication to magnetic resonance imaging (MRI)
  
• May be helpful to better define bony lesions
  
• Artifacts from pins may obscure target lesion

Digital Subtraction Angiography

• Used in conjunction with MRI or computed tomography for arteriovenous malformations (AVM) radiosurgery
  
• The AVM and regional arteries and veins need to be imaged.
  
• Must verify that images include all nine fiducial markers

Patient File Creation

• Enter patient demographic and clinical information.
  
• The skull and frame measurements are entered and checked for accuracy.

Setting Up Images in Planning Computer

• The stereotactic images are imported via Ethernet or scanned into the planning computer.
  
• Confirm images are from the right patient.
  
• The stereotactic space is defined for each set of images.
  
• The quality of images is rechecked (fiducials) because of possible distortion during image transfer.

Target Outlining

• Useful when the target volume is not clearly identified
  
• Helpful to assess conformality of the radiosurgery volume

Dose Planning

Radiation Delivery

• Valid radiosurgery protocol is printed and exported to delivery computer.
  
• The patient is secured in the radiosurgical device and every isocentric position is checked before radiosurgery can proceed.