What factors do you use to determine whether an enlarging lesion after SRS is radionecrosis versus progression?

This is a challenging issue, especially in a community setting where patients had not been treated with SRS before, and radiologists are now confronted with post SRS scans.

The two major things that clinicians can look at are:

1) T2 - T1 mismatch - if there is a correspondence between the contrast-enhancing volume on T1 and a low signal-defined lesion margin in the corresponding T2 images, then it is likely progression. If there is no clear and defined lesion margin on the T2 images, it is much m...