Early effects of PRS-irradiation for 9L gliosarcoma: Characterization of interphase cell death

We characterized the interphase cell death of 9L gliosarcoma after high-dos e-rate, low-energy photon irradiation using the Photon Radiosurgery System (PRS), a novel device for interstitial radiotherapy. Within 24 hours after irradiation with a dose of 18 Gray, 22.0% of cells underwent metabolic cell death, whereas dead cells in controls stayed less than 5.0% (p < 0.005). I n the majority of sensitive cells, loss of membrane integrity preceded the lethal morphological changes. The response was dose-dependent over the rang e of 9-18 Gray, but saturation was obtained over 18 Gray. On the other hand , a significant (p < 0.01) increase in the number of TUNEL-positive cells w ith apoptotic morphology was detected 6-24 hours after irradiation, but the fraction remained 1.9-2.1% of the population and was independent of the do ses between 9 and 25 Gray. Apoptotic cells were rarely observed in the cont rol cells (0.3-0.6%). Our data indicate that single high-dose irradiation i nduces both necrotic and apoptotic interphase cell death in 9L gliosarcoma, but rapid cell death mostly occurs through the non-apoptotic pathway.