Introduction: For large brain metastasis (≥2cm), staged stereotactic radiosurgery (SSRS) is used to improve control rates over single fraction SRS alone. However, perfusion MRI metrics measured throughout treatments and their association with local failure (LF) and radiation necrosis (RN) risk have yet to be evaluated.
Methods: Patients treated with SSRS (15Gy per session) with perfusion imaging from 2017-2023 were included. Primary endpoints were disease control (DC, stable disease, partial and complete response) and development of RN, recorded on a per-lesion basis. Tumor volume (TV) (cc) and mean relative-cerebral-blood-volume (rCBVmean) were extracted from MRI scans (baseline (before 1st SSRS), interim (before 2nd SSRS), post-treatment (8 weeks after 2nd SSRS)). Comparisons were made between DC vs. LF and RN vs. RN-free cohorts using Kruskal-Wallis, statistical significance at p<0.05.
Results: 30 patients (39 lesions) met inclusion criteria. Median TV: 5.6cc.(range: 1.2-27.8cc.) with primary histology of lung (47.5%) and breast (20.0%) cancer. 5.2% had LF, while 20.5% developed RN, with median times to LF and RN of 6.5 (R: 2-11) and 8.5 (R:4–54) months, respectively. For DC vs. LF, median interim change in TV (ΔTV) was -53.2% [-61.4% to -31.6%] vs.+14.17% [-71.8% to 100.2%] p=0.70 and post-treatment ΔTV was -43.7% [-64.8% to -24.9%] vs. -42.2% [-47.39% to -37.1%], p =0.95. Similarly, for RN vs. RN-free cohorts, interim ΔTV was -27.6% [-53.0% to -15.7%] vs.-56.0% [-67.0% to -37.0%] p=0.05 and post-treatment ΔTV was -25.1% [-44.0% to -0.3%] vs.-47.4% [-65.5% to -30.5%], p=0.06. Median-rCBVmean for DC vs. LF: Baseline:2.47 [1.8 to 4.17] vs. 2.62 [2.47 to 2.77], p=0.82; Interim:1.77 [1.24 to 2.36] vs.1.49 [1.15 to 1.82], p=0.59; Post-treatment:1.41[1.08 to 2.16] vs.0.71[0.68 to 0.73], p=0.06. For RN vs. RN-free lesions, median-rCBVmean: Baseline: RN:2.34 [1.89 to 2.73] vs. RN-free:2.54 [1.91 to 4.58], p=0.31; Interim: RN:1.82 [1.44 to 2.06] vs RN-free:1.74[1.20 to 2.46], p=0.93; Post-treatment: RN:1.26[0.93 to 1.57] vs. RN-free:1.41[1.07 to 2.20], p=0.50.
Conclusions: Lesions that developed RN exhibited less TV reduction on the interim MRI scan. Although rCBVmean decreased with treatment in most lesions, no clear correlation with clinical outcomes was observed. Larger studies incorporating refined perfusion analysis and advanced imaging techniques, such as novel PET tracers, are necessary to further clarify the prognostic value of these metrics.
