Radiosurgery Pathological Fundamentals

Because of the huge clinical experience that has been accumulated in radiosurgery, it seems timely to explore systematically the pathological fundamental effects of focused irradiation. A better understanding of radiobiology will enhance the outcomes of radiosurgical therapeutic procedures. The goal of this radiopathological study was to explore both short- and long-term tissue reactions evoked by single high-dose irradiation in different human brain tumors and experimental animals following Gamma Knife stereotactic radiosurgery (GK SRS). Histopathological investigations demonstrated that GK SRS generates degenerative and proliferative tissue reactions in the parenchyma, stroma, and vessels of the irradiated target volumes. Three predominant histological types of gamma radiolesions were identified: acute, subacute, and chronic variations of tissue reactions were recognized in different neoplasms irrespective of their ontogenetic nature. There was no significant relation between morphological characteristics of the evoked histological reaction and the time interval elapsed after GK SRS. This relative time and environment autonomy of the developed pathological lesions with a similar histological picture in different neoplasms suggests either a vascular mechanism or unique changes induced by the ionizing energy of high-dose photon irradiation in individual tumors.