Radionecrosis and cellular changes in small volume stereotactic brain radiosurgery in a porcine model

Stereotactic radiosurgery (SRS) has proven an effective tool for the treatment of brain tumors, arteriovenous malformation, and functional conditions. However, radiation-induced therapeutic effect in viable cells in functional SRS is also suggested. Evaluation of the proposed modulatory effect of irradiation on neuronal activity without causing cellular death requires the knowledge of radiation dose tolerance at very small tissue volume. Therefore, we aimed to establish a porcine model to study the effects of ultra-high radiosurgical doses in small volumes of the brain. Five minipigs received focal stereotactic radiosurgery with single large doses of 40–100 Gy to 5–7.5 mm fields in the left primary motor cortex and the right subcortical white matter, and one animal remained as unirradiated control. The animals were followed-up with serial MRI, PET scans, and histology 6 months post-radiation. We observed a dose-dependent relation of the histological and MRI changes at 6 months post-radiation. The necrotic lesions were seen in the grey matter at 100 Gy and in white matter at 60 Gy. Furthermore, small volume radiosurgery at different dose levels induced vascular, as well as neuronal cell changes and glial cell remodeling.

Radiation damage in soft X-ray microscopy of live mammalian cells

When specimens are observed by soft X-ray microscopy, they always absorb many photons, causing radiation damage at the imaged site. The problems of radiation damage were studied in view of the principle of image formation; absorption contrast, scattering (holography), or phase contrast. In all cases, photons with a wavelength of 1-10 nm interact with the specimen mainly through the photoelectric effect followed by the transfer of energy to the imaging site either directly (absorption imaging) or indirectly (holography or phase contrast). This absorbed energy will cause structural changes to the imaging site. From a review of the literature the absorbed dose is estimated to be as high as 10(7) Gy when the expected resolution of the specimen (1-10 microns thick) is 10 nm. This dose is far in excess of the amount required for cells to be able to survive when live mammalian cells are exposed. The levels of radiation effects were extrapolated to the estimated absorbed dose from the reported values for cell survival, chromosome aberrations, and DNA strand breaks with respect to observations on mammalian chromosomes. The extrapolated results show that some damage will occur in every 10 x 10-nm (expected resolution) size unit. Although these studies focused only on the effects on mammalian chromosomes, the present results are more or less common phenomena in the observation of biological specimens. Hence, the results suggest that dynamic observations will be difficult. On the other hand, a time-scale study of the effects of radiation on structural integrity suggests that single-shot imaging with short-pulsed (probably shorter than a few milliseconds) X-rays may be appropriate for the observation of intact live biological specimens in the hydrated condition, before they have deteriorated.

X-ray-induced chromosome damage in live mammalian cells, and improved measurements of its effects on their colony-forming ability

We have improved the precision of the technique described by Grote et al. (1981 a,b) for the observation of the radiation responses of live cultured mammalian cells with an incubated phase-contrast microscope: the colony-forming abilities of single cells obtained by selective detachment of mitoses (instead of cell pairs as previously) may now be followed individually and may be directly compared with chromosome damage detected after post-radiation mitosis (M1). An X-ray dose of 1.4 Gy to diploid Syrian hamster cells (BHK 21 C13) in G1 had no effect on cell ability to reach M1. If chromosome fragment loss was then detected (as micronuclei) in the daughter-cell pair then colony-forming ability nearly always deteriorated, and either a stop-growth (79 per cent) or a slow-growth (21 per cent) colony resulted; but chromosomal bridges which persisted beyond M1 broke during interphase 1 and themselves caused no detectable cell damage additional to that attributable to the micronuclei which accompanied them.

The human acoustic neurinoma in organ culture. II. Tissue changes after gamma irradiation

Acoustic neurinoma tissue in organ culture was exposed to gamma irradiation (60CO) 30-150 Gy single dose. Schwann cell degeneration occurred from the first week onward in vitro following irradiation. After 3 weeks only a limited number of surviving cells were observed in the specimens, as compared with controls. The in vitro changes in tissue morphology indicate an irreversible course even after irradiation with the lowest dose, 30 Gy single dose. As a comparison with the in vitro experimental material it has also been possible to analyse the light and electron microscopic morphology of a tumour from a patient previously treated with stereotactic radiosurgery. An similar substantial Schwann cell loss was found in the centre of the tumour treated with stereotactic irradiation prior to surgery, as compared with the in vitro material.