Radiotherapy-induced brain injury: a role for PET and SPECT imaging?

Irradiation of brain tumors not only kill tumor cells, but can also induce damage to normal cells, which can eventually lead to detrimental effects. The neuroimaging techniques PET and SPECT could be applied to investigate radiotherapy-induced brain-injury in a longitudinal manner. These techniques might be able to detect molecular and functional changes before symptoms or anatomical abnormalities present themselves.

We aimed in this study of Andrea Parente to obtain more insight in the status of the normal brain after radiotherapy using PET and SPECT with various tracers. For this purpose, we irradiated the whole brain of healthy rats and monitored the animals for up to 90 days using behavioral tests and neuroimaging. In particular, we studied the radiation-induced effects on neuroinflammation, myeline-density, brain metabolism and cerebral blood flow, using PET and SPECT.

The studies showed that whole brain-irradiation led to an increase in brain metabolism, cerebral blood flow, and microglia activation in the acute phase after irradiation (day 3-12), indicating an acute inflammatory response was induced. In the early-delayed phase (month 1-2), some neuroinflammation was still present and a trend towards a decrease in myelin density was observed, which recovered in the late-delayed phase. At the start of late-delayed phases (month 2-3), a reduction in brain metabolism appeared, which could indicate late degeneration was occurring. At this stage, outcome measures of memory tests correlated with myelin-density in the irradiated group. Thus, we showed that PET and SPECT are useful techniques for in-vivo monitoring of the sequential effects of radiotherapy on non-tumorigenic brain tissue.