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Top Line: Do immune checkpoint inhibitors (ICI) increase the risk of toxicity with stereotactic radiosurgery (SRS)?
The Study: This is a never-ending question, and many of us are left not knowing exactly what to ask for when it comes to peri-SRS ICI administration. Here’s a large single-institution review from Wake Forest of SRS with or without ICI onboard. They considered ICI exposure in two ways: any exposure at all and “concurrent” exposure +/-30 days of SRS. Over 2000 metastases in nearly 300 patients were analyzed. Among those, 56% were ever exposed to ICI with roughly half of those having received ICI concurrent with SRS. All patients were treated with GammaKnife and received a median 20 Gy in 1 fraction prescribed to the 50-60% isodose line of the GTV with no PTV margin. Recorded adverse radiation effects (ARE) ranged from sub-acute symptomatic edema to pseudoprogression to necrosis. Overall, 2.6% of treated lesions developed some ARE at a median of 6 months. However, the rate of ARE was higher (3.4% versus 1.6%) and median time to ARE was shorter (6 versus 9 months) with ICI exposure. Among these ICI recipients, though, treatment within 30 days of SRS did not increase the risk of ARE. And it's not like you can really control the fact that a patient has received ICI. Finally, the biggest modifiable risk factor of ARE among ICI recipients was brain V12 in a continuous fashion, although it’s not clear from this study if fractionated SRS would lower that risk.
TBL: While this study confirms a potential increased risk with SRS in the setting of any ICI exposure, the timing of ICI didn’t seem to matter. | Helis, Int J Radiat Oncol Biol Phys 2020