Novalis Shaped Beam Surgery surpasses the older Gamma Knife for stereotactic radiosurgery by every relevant measure. Gamma Knife can deliver stereotactic radiosurgery to small spherical lesions with millimeter accuracy, but the dose gradient is not as sharp as with Novalis, necessitating irradiation of a larger volume of tissue surrounding the target volume.
For larger, irregularly shaped target volumes, the Gamma Knife treatment produces significant hot and cold spots withint the target volume as a result of multiple overlapping spherical dose volumes. With Novalis, a large intracranial target volume with an irregular shape can be treated very efficiently using dynamic arcs.
With a dynamic arc treatment, the shape of the beam changes continuously to conform to the shape of the target volume. As a result of these differences, the minimum dose to a target volume with Novalis is typically 80-90 percent of the maximum dose, compared to 50 percent for Gamma Knife.
| |
Novalis Shaped
Beam Surgery |
Cyber
Knife |
| Image-guided positioning using stereo x-ray images |
Yes |
Yes |
| Image-guided stereotactic IMRT |
Yes |
Yes |
Uniform dose to irregularly shaped volumes
* Irregular volumes can be treated with shaped beam dynamic arcs or IMRT
** Treatment requires multiple overlapping circular beams |
Yes* |
No** |
| No invasive implantation of fiducial markers for spine treatment |
Yes |
No |
Dynamic handling of respiratory motion for treatment of lung and liver
*Novalis: Respiratory gating of radiation beam
**CyberKnife: Dynamic image-guided repositioning during treatment |
Yes* |
Yes** |
The advantages of Novalis Shaped Beam Surgery over CyberKnife are mainly due to the unique micro-multileaf collimator (mMLC) that is used to dynamically shape the Novalis beam or to modulate the intensity of the beams for IMRT. With CyberKnife, the beam is defined with a fixed circular collimator rather than a multileaf collimator. This results is two significant limitations as compared with Novalis Shaped Beam Surgery.
1. An irregular volume must be treated with multiple overlapping circular beams, resulting in hot and cold spots in treatment volume.
2. CyberKnife has a limited ability to spare sensitive normal tissues as compared with IMRT.
With Novalis, a target volume with an irregular shape can be treated very efficiently using dynamic arcs, for which the shape of the beam dynamically changes to conform to the shape of the target volume as the machine rotates around a single isocenter within the target volume. If sensitive normal structures are in close proximity to the target volume, IMRT can be used to deliver a therapeutic dose to the target volume while sparing the proximate sensitive structures.
|
