Table 1.

Imaging changes after radiation therapy.

Parameter	Pseudoprogression	Treatment effect after radiosurgery	Radionecrosis	Tumor progression
Time to onset	2–6 months after RT	3–12 months after RT	6–12 months after RT (but can be decades)	Any
Characteristic imaging appearance	Contrast enhancement with FLAIR hyperintensity	Contrast enhancement with FLAIR hyperintensity	Contrast enhancement with FLAIR hyperintensity; ‘soap bubble’ or ‘Swiss cheese’ sign	Contrast enhancement with FLAIR hyperintensity
Treatment	Observation with close follow-up	Observation with close follow-up	Steroids, bevacizumab, surgical resection	Tumor-directed therapy
Usually symptomatic?	No	No	Yes	Yes
MRI spectroscopy	Not clearly radionecrosis or tumor progression	Not clearly radionecrosis or tumor progression	Relatively less choline	Relatively less NAA and creatine; more choline and lactate
Diffusion weighted imaging	Not clearly radionecrosis or tumor progression	Not clearly radionecrosis or tumor progression	Less restricted diffusion (lower signal)	More restricted diffusion (higher signal)
Dynamic contrast imaging	Relatively low mean cerebral blood volume compared with true tumor progression	Relatively low mean cerebral blood volume compared with true tumor progression	Relatively low mean cerebral blood volume compared with true tumor progression	Relatively high mean cerebral blood volume

FLAIR: Fluid attenuated inversion recovery; RT: Radiation therapy.