PULSE SIGNAL SCATTERING FROM PERFECTLY CONDUCTING COMPLEX OBJECT LOCATED NEAR UNIFORM HALF-SPACE

Abstract-The approximative calculation technique of the pulse signal backscattering for the perfectly conducting electrically large object (with small curvatures) located near the boundary of the uniform half-space (perhaps, with the complex parameters) is proposed. The calculation results of electromagnetic fields scattered from perfectly conducting sphere and complex shape objects located near the ground surface are demonstrated and discussed

STEREOTACTIC RADIOTHERAPY AND RADIOSURGERY IN THE TREATMENT OF PATIENTS WITH BRAIN PILOID ASTROCYTOMAS OF DEEP LOCATION

Piloid astrocytoma (PA) is a low-grade (WHO grade I) glial tumor that is more common in pediatric patients. According to the data of many authors, stereotactic radiosurgery (SRS) and stereotactic radiotherapy (SRT) promote long-term remission or delayed tumor progression in patients with inoperable tumors after incomplete removal of a tumor and with its recurrence. So it is urgent to determine the place and role of SRS and SRT in the combination treatment of patients with deeply located PA.Subjects and methods. In the period April 2005 to May 2010, the Department of Radiology and Radiosurgery, Neurosurgery Research Institute, Russian Academy of Medical Sciences, treated 101 patients diagnosed as having intracranial PA. Of them there were 70 children (aged 17 years inclusive) and 31 adults; 51 men and 50 women. The median age was 15.1 years (9.8 years for children and 28.7 years for adults). Tumor was histologically pre-verified in 90 (89.2 %) patients (tumor ablation in 83 cases and biopsy in 7). The diagnosis of PA was made on the basis of clinical and X-ray data in 11 (10.8 %) patients. ART was used in most cases (n = 66 (66.3 %)). SRS was performed in 35 (34.7 %) patients.Results. The median follow-up of the patients from the onset of disease was 52 months (range 2–228 months). Eighty-eight (87 %) patients could be followed up. On completion of the follow-up (December 2010), 87 (98.8%) of the 88 patients receiving SRT and SRS were alive. The median follow-up from the initiation of radiotherapy was 22.7 months (range 6–60 months). Tumors were enlarged in 20 (22.7 %) patients; those were due to cysts in 18. Eighteen patients were reoperated on. Histological specimens were examined and comparatively analyzed in 12 operated patients. The tumor changes accompanied by a reduction of the solid component and an increase of the cystic component were found to be a manifestation of tumor reactive-degenerative alterations as a consequence of radiation pathomorphi sm.Conclusion. SRT and SRS are effective treatments in patients with primary or recurrent PA irrespective of the tumor site and must be performed early after non-radical tumor removal. At present (median follow-up 22.7 months), tumor growth is controlled in 98 % of th