Analysis of the proliferative potential of tumor cells after stereotactic radiosurgery for recurrent astrocytic tumors

We analyzed the effectiveness of stereotactic radiosurgery (SRS) for recurr ent astrocytic tumors histologically. Five patients were followed by pathol ogical examination after radiosurgical treatment of recurrent astrocytic tu mors. Histological diagnoses at the time of the last operation before SRS w ere Daumas-Duport grade II in two patients and grade IV (glioblastoma) in t hree patients. No histological diagnoses at the time of SRS were identified in any patients. Contrast enhanced lesions enlarged gradually on magnetic resonance (MR) images after SRS, and local control by SRS was judged as pro gressive disease radiologically in all patients. Four of five patients rece ived re-operation after SRS, and the other patient died without re-operatio n and underwent post-mortem examination. After SRS, Ki-67 labeling indices (Lls) of recurrent astrocytomas initially diagnosed as grade II were 2.6% a nd 1.1%. These Lls were relatively lower than those of the control group of patients with recurrent grade II astrocytomas that were not treated by SRS . Ki-67 Lls of three glioblastomas after SRS were 23.5%, 18.6%, and 17.8%. These Lls were significantly lower than those before SRS (2.3%, 4.5%, and 0 .9%). In the autopsy case, there was a significant difference between the L I of tumor cells in the radiosurgically treated region (0.9%) and that in t he untreated region (29.2%). These results suggest that the proliferative p otential of malignant astrocytic tumors in the radiosurgically treated area is reduced after SRS, and that radiological enlargement of enhanced lesion s on MR images is due to propagation of the residual tumor cells that were not covered by radiosurgical target volume or to radiation necrosis. SRS ma y be a useful therapeutic tool in multidisciplinary treatment of malignant gliomas.