**3. Complications of SRS**

Adverse radiation effects due to SRS include focal edema and radionecrosis. These effects correspondingly intensify with the tumor volume and radiation dose and found more frequently in patients who received boost SRS concurrently with RT. Frequency of adverse radiation effects range between 0 to 40% in different series, albeit it's uncommonly more than 5%. These effects are usually completely reversible with anti-edema medications and rarely results in permanent neurological complications. Previous irradiation history should

Finally, the best candidates for SRS treatment are the pilocytic astrocytomas if previously resected, well circumscribed, and located in critical or deep areas or re-resection is not

While ependymomas are classified as grade II in WHO grading system, the anaplastic ependymomas are grade III tumors. However the local tumor control has a great importance for ependymoma management, high propensity of seeding through ventricular system and central canal serves as a problem. The most prominent poor diagnostic factor is the spinal metastasis for ependymomas. Current treatment modality includes surgical resection followed by RT. Chemotherapy is also indicated for anaplastic ependymomas. Better local tumor control for ependymomas with SRS has been reported in limited number of preliminary studies. Results with boost SRS + RT are better than SRS for late recurrences conversely to other gliomas. There is a proportion between time to recurrence and success rate for adjuvant SRS. 100% TCR was found at a mean 21 months follow up in a series of 22 anaplastic ependymoma patients following adjuvant SRS (Jawahar et al., 1999). But 44% patients recurred at a distant site of the CNS in further follow ups. Definite predictors of

better prognosis for SRS treatment for ependymomas are; (Kano et al., 2009d, 2010)

Homogeneous contrast enhancement on MRI for low grade ependymomas

Interestingly, no significant relation was found between the grade of the tumor and PFS. SRS seems a valuable treatment option for local control of recurrent or residual ependymomas. On the other hand, the distant seeding and recurrences of the tumor is a

Only seldom studies are available regarding to the effectiveness of SRS for oligodendroglioma and oligoastrocytoma in current literature. A study on SRS for oligodendroglioma reported 5 and 10 year overall survival rates of 90.9% and 68.2% for grade II, and 52.1% and 26.1% for grade III oligodendroglioma, respectively (Kano et al., 2009c). Tumor volume less than 15 cc and patients with 1p19q gene deletion are related with better outcome. Another study on SRS including oligodendroglioma and oligoastrocytoma patients suggested that the younger age is also associated with better outcome (Sarkar et al.,

Adverse radiation effects due to SRS include focal edema and radionecrosis. These effects correspondingly intensify with the tumor volume and radiation dose and found more frequently in patients who received boost SRS concurrently with RT. Frequency of adverse radiation effects range between 0 to 40% in different series, albeit it's uncommonly more than 5%. These effects are usually completely reversible with anti-edema medications and rarely results in permanent neurological complications. Previous irradiation history should

2002). Further studies are needed to assess the effectiveness of SRS for these entities.

Time interval between RT and recurrence > 18 months

**2.4 Oligodendroglioma and mixed oligoastrocytoma** 

pain in the neck (Krieger & McComb, 2009; Lo et al., 2006a, 2006b).

feasible, or if there is an early recurrence.

 Absence of spinal metastasis Lower tumor volume

**3. Complications of SRS** 

**2.3 Ependymoma** 

be considered particularly for lesions located in eloquent areas and dose should be reduced. Aggressive irradiation might result in excessive edema and radionecrosis requiring additional procedures such as emergent decompression or shunting (Smith et al., 2008). Radiation induced tumors is another potential complication of SRS. Several sporadic reports of GBM formation in long term following high dose SRS are already present. However long term follow up is needed to assess this potential, incidence seems less than 1:100.000 for now (Berman et al., 2007; Salvati et al., 2003).
