Single vs Multi-fraction SRS Patients on Immunotherapy

Inclusion Criteria:

i. Adult patients (≥ 18 years old) with an ECOG Performance Status 0-2 and a life expectancy of 3 months or more.

ii. Histologically confirmed systemic malignancy with gadolinium contrast-enhanced MRI scan demonstrating 1-10 newly diagnosed intraparenchymal brain metastases.

iii. Well-circumscribed, measureable intraparenchymal brain metastasis(s) with maximum tumor diameter ≤3.0 cm. If multiple metastases are present, the other(s) must not exceed 3.0 cm in maximum diameter. At least one metastasis must be ≥ 0.5 cm in maximum diameter to be considered measurable disease.

iv. Negative urine or serum pregnancy test done ≤ 21 days prior to CT simulation, for women of child bearing potential only.

v. Ability to understand and willingness to sign a written informed consent document.

vi. Must have received immunotherapy (PD-1/PD-L1 and/or CTLA-4 inhibitor(s)) within the past 6 months or plan on receiving immunotherapy within the next 1 month.

vii. Must have a Gustave Roussy Immune Score (GRIm-Score) of 0 or 1 (neutrophil-to-lymphocyte ratio \> 6 = 1 point, LDH \> Upper Limit of Normal = 1 point, and Albumin \< 3.5 g/dL = 1 point).

Exclusion Criteria:

i. Diagnosis of germ cell tumor or hematologic malignancy. ii. Metastases in the brain stem, midbrain, pons, medulla, or within 7 mm of the optic apparatus (optic nerves, chiasm and optic tracts).

iii. Diagnosis of leptomeningeal disease. iv. Prior SRS to an immediately adjacent lesion(s) of interest or to the current lesion(s) of interest.

v. Prior history of pseudoprogression or radionecrosis from cranial radiotherapy.

vi. A neurosurgical resection cavity deemed too large by the radiation oncologist to be treated with a single fraction of stereotactic radiosurgery.

vii. Contraindications to gadolinium contrast-enhanced MRI (eg, non-compatible pacemaker, eGFR \<30, gadolinium allergy).

viii. A Gustave Roussy Immune Score (GRIm-Score) \> 1 (neutrophil-to-lymphocyte ratio \> 6 = 1 point, LDH \> Upper Limit of Normal = 1 point, and Albumin \< 3.5 g/dL = 1 point).