Staged Stereotactic Radiosurgery as a Novel Adaptive Approach to Salvage Previously Irradiated Brain Metastases

PURPOSE/OBJECTIVE(S)

We report outcomes specific to a novel 3 fraction (frx) staged stereotactic radiosurgery (St-SRS) regimen designed to salvage metastases previously irradiated and considered to be at high risk of radiation necrosis (RN).

MATERIALS/METHODS

A total of 24 patients with 55 metastases treated with our 3 frx St-SRS approach were reviewed. Prior to each frx, patients were re-simulated and planned with a new MRI to allow for treatment adaption. The primary endpoint was the cumulative incidence of local failure (LF) and secondary endpoints included tumor dynamics and RN rates.

RESULTS

The median follow up was 9.0 months (range: 2.7-40.1 months) and median age was 59-years (range: 32-84). Primary cancers were of breast (44%), lung (33%), melanoma (22%), and gastro-intestinal (1%) origin. Individual metastases treated with St-SRS had initially failed surgery and post-op cavity hypofractionated SRS (HSRS) for 2/55 (4%), SRS alone for 19/55 (34%), whole brain radiation (WBRT) alone for 6/55 (11%), HSRS for 2/55 (4%), and prior SRS and WBRT exposure for 28/55 (51%). 46/55 (84%) were prescribed 8 Gy, 8 Gy, 4 Gy; 8/55 (14%) had 6 Gy, 6 Gy, 4 Gy and 1/55 (2%) had 8 Gy, 8 Gy, 6 Gy. The median number of weeks between frx was 2.6 (range: 1.0-6.8). The median of the mean and maximum target doses were 9.7 Gy (range: 5.4-11.7 Gy) and 12.4 Gy (range, 7.5-16.0 Gy) respectively. The median prescription isodose line was 62% (range: 50-85%). The mean lesion volume and diameter was 3.8cc (range: 0.05-24.8cc) and 1.6cm (range: 0.2-4.4cm), respectively. The mean percent target volume coverage, Paddick Conformality Index and Gradient Index were 100% (range: 97-100%), 0.7 (range: 0.1-0.9), and 3.2 (range: 2.5-6.7), respectively. The mean volume change between staged frxs was -4.2% (range: -69.3 to +63.1%), and based on the first and last St-SRS MRI was -10.8% (range: -86.6% to +68.7%). The crude LF rate was 27%. The median time to LF was 3.4 months (range: 1.2-7.4 months). Amongst those with a LF, 7/15 (46%) were melanoma, 6/15 (40%) HER2 positive breast cancer, 1/15 (7%) gastrointestinal and 1/15 (7%) non-small cell lung carcinoma. 8/15 (53%) had prior WBRT and SRS exposure, 1/16 (7%) surgery and cavity HSRS, 5/15 (33%) SRS alone and 1/15 (7%) WBRT alone. Only asymptomatic RN events were observed in 4/55 (7%).

CONCLUSION

St-SRS is a promising approach to salvage previously irradiated brain metastases, including prior SRS, with a favorable rate of RN. Tumor volume dynamics between stages can be significant warranting adaptive replanning.

Molecular Status Predicts for Local Control in Patients with Non-Small Cell Lung Cancer Spinal Metastases Following Spine Stereotactic Body Radiotherapy

PURPOSE/OBJECTIVE(S)

We report outcomes after spine stereotactic body radiotherapy (SBRT) in patients with metastatic non-small cell lung cancer (NSCLC), to determine the significance of programmed death-ligand 1 (PD-L1) status and epidermal growth factor (EGFR) mutation on local failure (LF) rate.

MATERIALS/METHODS

A total of 165 patients and 389 spinal segments were retrospectively reviewed from 2009 to 2021. Baseline patient characteristics, treatment and outcomes were abstracted. Primary endpoint was LF and secondary outcomes included overall survival (OS) and vertebral compression fracture (VCF) rates. OS was estimated using the Kaplan-Meier method. Cumulative LF and VCF rates were calculated using competing risk analysis method. Multivariable analysis (MVA) evaluated factors predictive of LF and VCF.

RESULTS

Median follow-up was 13 months (range, 0.5-95 months). Median OS was 18.4 months (95% CI 11.4-24.6). Median age was 67 years (range, 28.2-89.9). 52% were female, 76% had an adenocarcinoma histology and 61% had a smoking history. 49/165 (29%) had an EGFR mutation. PD-L1 status was analyzed in 109/165 (66%) patients with 16% PD-L1 ≥ 50%, 20% PD-L1 1-49% and 35% PD-L1 <1%. Of 389 segments, 79% were de novo and 21% were previously radiated. At baseline, 35% had a VCF, 27% had epidural disease, 27% had paraspinal extension, and 49% were Spinal Instability in Neoplasia Score (SINS) stable. 239/389 (61%) were treated with either 24 or 28 Gy in 2 SBRT fractions. Within 1 month of SBRT, 39/165 (24%) had a tyrosine kinase inhibitor, 27/165 (16%) immunotherapy (IO) with or without chemotherapy, and 31/165 (19%) chemotherapy alone. LF cumulative incidence at 1- and 2-years was 16.3% (95% CI 12.8-20.3%) and 25.4% (95% CI 20.9%-30%), respectively. EGFR positivity (p<0.0001), PD-L1≥50% (p = 0.013) and treatment with IO within 1 month of SBRT (p = 0.004) predicted for improved local control on MVA. The 1- and 2-year LF rate in EGFR-positive vs. negative patients were 12.9% vs. 16.6% and 17.7% vs. 28.8%, respectively, and in those PD-L1 ≥50% vs PD-L1<50% were 7.8% vs. 19.6% and 7.8% vs. 38.1% respectively. Cumulative incidence of VCF at 1- and 2-years were 6.6% (95% CI 4.4-9.4%) and 8.8% (95% CI 6.1-12.0%). MVA identified prior SBRT to the same treated segment (P<0.0001) and a baseline VCF (p<0.0001) as significant predictors. 18/389 (4.6%) had radiation-induced radiculopathy and no radiation myelopathy events detected.

CONCLUSION

We identify the predictive utility of EGFR mutation and PD-L1 ≥50% status on local control in NSCLC patients with spinal metastases treated with spine SBRT, and a therapeutic benefit with peri-SBRT IO.