*Overview of Radiosurgery for Intracranial Meningiomas DOI: http://dx.doi.org/10.5772/intechopen.100006*

surrounding. Mechanism of radiation related tumoricidal activity include DNA injury together with induction of apoptosis and vascular endothelial damage [10]. The advantages compared to other radiotherapy modalities include maximal conformity, rapid dose fall-off at radiation beam edges and minimal spatial inaccuracies in patient set-up, with generally very low radiation related toxicity (**Figure 2**) [11].

In current radiosurgery principle, the generally applied prescription dose is 12–16 Gy to the tumor margin at 50% isodense line [12]. Treatment dose need to be balanced with the radiation tolerance thresholds to those Organ-at-risk (OAR). A guideline with UK Consensus on normal tissue dose constraints for stereotactic radiotherapy was published as reference (**Table 4**) [19].

### **6. Radiosurgery techniques and current devices**

Dose selection is the basic but upmost significant step in planning of radiosurgery treatment. It is always a balance between the expected level of treatment success and complications risks at various doses so as to select the most optimal dose for the individual patient. The paired sigmoid dose–response curves illustrate the balance between increasing the desired response and increasing complications with higher radiation treatment doses, with the so-called therapeutic window is the area between the two curves (**Figure 3**). Another essential principles in radiosurgery planning are conformity and selectivity. Traditionally, stereotactic radiosurgery (SRS) refers to stereotactically guided delivery of focused radiation to a defined target volume in a single session. Most of the procedures are performed in stereotactic frame-based manner. Modern development of radiosurgery technique allows the fixation of patient's head on couch without the stereotactic frame i.e. frameless. Thus the concept of fractionated stereotactic radiosurgery (FSRS) evolved, or in better terminology, stereotactic radiotherapy (SRT).

Current choice of radiosurgery devices can be divided depends on the application of clinical beams. LINAC Radiosurgery makes use of either linear acceleratorsbased system or robot-assisted e.g. CyberKnife, while Gamma Knife Radiosurgery employs Cobalt (Co)-60 as the source (**Figure 4**). Both treatment of choices are effectively in treatment of intracranial meningiomas.

**Figure 3.** *Paired sigmoid dose–response curves for both desired response and complications.*

*Overview of Radiosurgery for Intracranial Meningiomas DOI: http://dx.doi.org/10.5772/intechopen.100006*

#### **Figure 4.**

*Models of radiosurgery system in Hong Kong (a) LINAC in our centre (b) CyberKnife in private hospital (c) Gamma Knife Icon in private hospital.*
