Hyperpolarized 13C lactate-to-bicarbonate signal ratio predicts brain metastases response to stereotactic radiosurgery

Background Brain metastases (BM) are increasingly treated with stereotactic radiosurgery (SRS); however, up to 30% of BM recur locally. This work investigated whether hyperpolarized (HP) [1-13C]-pyruvate MRI can be used to predict SRS treatment response in patients with BM. Methods Eighteen patients with 44 BM were imaged with HP [1-13C]-pyruvate MRI prior to SRS. Treatment response was determined using the Response Assessment in Neuro-Oncology BM (RANO-BM) working group guidelines at 6-month follow-up. Fourteen parameters, including lesion [1-13C]-lactate to [13C]-bicarbonate, [1-13C]-lactate to [1-13C]-pyruvate and [13C]-bicarbonate to [1-13C]-pyruvate signal ratios, in addition to prognostic and dosimetric parameters, were analyzed using univariable and multivariable analysis. Results Univariable analysis identified lesion [1-13C]-lactate to [13C]-bicarbonate ratio (P = .0003), lesion [13C]-bicarbonate to [1-13C]-pyruvate ratio (P = .0118), lesion volume (P = .0264), and the number of involved organs with metastases including the brain (P = .0448) as significant predictors of treatment response. The lesion [1-13C]-lactate to [13C]-bicarbonate ratio was predictive of response with the best overall performance, achieving an AUCROC = 0.88, AUCPRC = 0.83, sensitivity = 67% (CI: 40%–87%), specificity = 97% (CI: 90%–100%), and positive predictive value (PPV) = 91% (CI: 73%–100%). Conclusions HP lesion [1-13C]-lactate to [13C]-bicarbonate ratio can predict SRS response with a high PPV.