Factors associated with radiation necrosis and intracranial control in patients treated with immune checkpoint inhibitors and stereotactic radiotherapy

Background and purpose: Emerging data suggest immune checkpoint inhibitors (ICI) and stereotactic radiosurgery (SRS) or radiotherapy (SRT) may work synergistically, potentially increasing both efficacy and toxicity. This manuscript characterizes factors associated with intracranial control and radiation necrosis in this group.

Materials and methods: All patients had non-small cell lung cancer, renal cell carcinoma, or melanoma and were treated from 2013 to 2021 at two institutions with ICI and SRS/SRT. Univariate and multivariate analysis were used to analyze factors associated with local failure (LF) and grade 2+ (G2 + ) radiation necrosis.

Results: There were 179 patients with 549 metastases. The median follow up from SRS/SRT was 14.7 months and the median tumor size was 7 mm (46 tumors ≥ 20 mm). Rates of LF and G2 + radiation necrosis per metastasis were 5.8% (32/549) and 6.9% (38/549), respectively. LF rates for ICI +/- 1 month from time of radiation versus not were 3% (8/264) and 8% (24/285) (p = 0.01), respectively. G2 + radiation necrosis rates for PD-L1 ≥ 50% versus < 50% were 17% (11/65) and 3% (5/203) (p=<0.001), respectively. PD-L1 ≥ 50% remained significantly associated with G2 + radiation necrosis on multivariate analysis (p = 0.03). Rates of intracranial failure were 54% (80/147) and 17% (4/23) (p = 0.001) for those without and with G2 + radiation necrosis, respectively.

Conclusions: PD-L1 expression (≥50%) may be associated with higher rates of G2 + radiation necrosis, and there may be improved intracranial control following the development of radiation necrosis. Administration of ICIs with SRS/SRT is overall safe, and there may be some local control benefit to delivering these concurrently.