Predicting response to radiotherapy of intracranial metastases with hyperpolarized $^{13}$C MRI

Background: Stereotactic radiosurgery (SRS) is used to manage intracranial metastases in a significant fraction of patients. Local progression after SRS can often only be detected with increased volume of enhancement on serial MRI scans which may lag true progression by weeks or months. Methods: Patients with intracranial metastases (N = 11) were scanned using hyperpolarized $$^{13}$$13 C MRI prior to treatment with stereotactic radiosurgery (SRS). The status of each lesion was then recorded at six months post-treatment follow-up (or at the time of death). Results: The positive predictive value of $$^{13}$$13 C-lactate signal, measured pre-treatment, for prediction of progression of intracranial metastases at six months post-treatment with SRS was 0.8 $$p < 0.05$$p < 0.05 , and the AUC from an ROC analysis was 0.77 $$p < 0.05$$p < 0.05 . The distribution of $$^{13}$$13 C-lactate z-scores was different for intracranial metastases from different primary cancer types (F = 2.46, $$p = 0.1$$p = 0.1 ). Conclusions: Hyperpolarized $$^{13}$$13 C imaging has potential as a method for improving outcomes for patients with intracranial metastases, by identifying patients at high risk of treatment failure with SRS and considering other therapeutic options such as surgery.