Can a second course of SRS be used to treat a brain met that initially responded to SRS and then progressed?

One should use caution in interpreting imaging as a definitive sign of progression, as sometimes radiation necrosis can mimic those findings. if asymptomatic, the patient can be considered for close observation with imaging and if symptomatic, one should consider a surgical option also.

If there is compelling evidence for recurrence, there are a few small case series that demonstrate feasibility of repeat SRS. We recently presented our own series at ASTRO (http://www.redjournal.org/article/S0360-3016(14)01740-4/fulltext) demonstrating a 1y LRFS of 62.4% with 17% risk (4 pts) of grade 3 CNS toxicity after 2 courses of single fraction SRS to the same lesion. In many of the patients, the same dose was used the 2nd time. So, while it is feasible and may represent the best alternative if surgery (or other local control options such as AutoLITT) is not an option, at least in our cohort there is some reasonable risk of toxicity and local control that leaves something to be desired. As such, we are exploring the use of fractionate...

I agree with caution in interpreting the results of PET and MRI spectroscopy. The specificity of PET, MRI, and MR spectroscopy vary from 50-80%. We have had a number of cases in which PET and MR spec were consistent with progressive disease and surgical pathology on the whole lesion showed radionecrosis without any tumor. It can be extremely difficult to distinguish between disease progression and radionecrosis on imaging, and the worst thing to do would be to give a second course of SRS to an area of radionecrosis (we’ve seen this from outside hospitals, with devastating results). The standard at our center is to refer patients to neurosurgery for a biopsy to confirm progressive disease before offering repeat-SRS. When an MRI report calls ...