Treatment
Patients treated with nivolumab received intravenous infusions at a dose
of 3 mg/kg once every two weeks. A cycle of therapy was operationally
defined as 28 days, during which nivolumab was administered on day 1 and
day 14. Patients treated with pembrolizumab received intravenous
infusions at a dose of 2 mg/kg once every three weeks. A cycle of
therapy was operationally defined as 21 days, during which pembrolizumab
was administered on day 1 and day 21. Treatment was repeated every 14
days for nivolumab, and every 21 days for pembrolizumab, provided all
hematologic toxicity from the previous cycle had resolved to grade 2 or
less, and all non-hematologic toxicities recovered to either grade 1 or
less. When indicated, the subsequent ICI cycle was delayed until these
criteria were met.
Radiotherapy planning volumes were contoured by a radiation oncologist
and a neurosurgeon. Dose and fractionation were determined on the basis
of lesion size, prior radiotherapy, and meeting dose constraints for
adjacent organs at risk. For treatment planning, high-resolution
thin-slice magnetic resonance T1 sequences with contrast were rigidly
fused to CT simulation scans. All patients were treated using
non-coplanar volumetric modulated arc therapy (VMAT) using 3-4 arcs and
either 6X or 10X flattening filter-free beams that maintained a minimum
coverage of 95% of the planning target volume receiving 100% of the
prescription dose. The treatment plans were generated using Eclipse
v15.6 (Varian Medical Systems, Palo Alto, CA) with either AAA or
AcurosXB calculation algorithms. All dose constraints for SBRT plans
were evaluated using TG101 guidelines. Patients were treated on a
Novalis (BrainLab, Munich, Germany) Truebeam STX linac (Varian Medical
Systems, Palo Alto, CA), with multileaf collimator leaf width of 2.5 mm.