Long term outcomes of fractionated Stereotactic Radiosurgery (fSRS) for benign meningiomas

Summary: Radiation is commonly used to treat intracranial meningiomas. Various radiation dosing regimens exist due to tumor size, location, and patient preference. Meningiomas are slow growing, necessitating long follow-up periods to gather pertinent clinical data. This study evaluated the long-term outcomes of patients with benign meningiomas treated with fSRS at our institution. This is a retrospective review of all patients diagnosed with meningioma at our institution who received fSRS (5 fractions). Clinical data, including tumor location, size, prior treatments, demographics, radiation dosimetric information, tumor response, and survival were collected. Kaplan-Meier curves were used to assess local control. Acute and late toxicities were evaluated. Patients were included for analysis if they had at least one post-treatment MRI following therapy. 88 patients with low-grade meningiomas treated between 2013 and 2022 were identified with 72 included for analysis (n=16 excluded due to lack of follow-up). The median age was 66 years (range 21-89), with 80.5% identifying as White, 12.5% as Black, 1% as Asian, 1% as Hispanic, and 1% as Native American. The median Karnofsky Performance Status (KPS) before treatment was 90 (range 50-100). Half of the patients (n=35) had prior surgical resection, with 40% (n=14) achieving gross total resection (GTR). About 10% (n=7) had received prior radiation for the treated meningioma. Tumor locations included the cerebellopontine area (9.7%), prepontine and cerebellar areas (8.3%), parasagittal or parafalcine regions (11.1%), cavernous sinus (12.5%), olfactory groove (2.7%), sphenoid area (11.1%), and various other intracranial sites (44.4%). 16 (22.2%) patients were treated with gamma knife (GK), while the remainder received treatment via TrueBeam Linac. The median tumor volume was 7 cc (range 0.4-94.2), and the median planning target volume (PTV) was 11.3 cc (0.4-116.4 cc). The median of the mean PTV dose is 27.82 Gy and minimum and maximum doses of 22.41 Gy and 29.89 Gy, respectively. With median follow-up of 38.0 m, the 1-year, 3-year, and 5-year local control rates were 98.6%, 93.15%, and 87.51% respectively. 42 (58.3%) patients had partial improvement or resolution of presenting symptoms after completing radiation. When conducting a subgroup analysis excluding patients previously treated with radiation, local control improved to 95.64%, 94.07%, and 90.15% at 1, 3, and 5y respectively. 13 patients (18%) had G1 or G2 toxicities with 5 of them experiencing G2 radionecrosis. When tumors were categorized by size as small (10cc), Chi-squared analysis showed no difference in the rate of failure (chi-square=0.85, p=0.65). The SRT regimen of 25 Gy in 5 fractions effectively achieves local control and safety in low-grade meningiomas. Many patients had prior radiation or surgery, with some revealing high-grade disease. These findings highlight the need for further clinical studies to better understand grade 1 meningiomas. Shray Jain (he/him/his), BS, MS (Presenting Author) - Drexel University College of Medicine; Nilanjan Haldar (he/him/his), MD (Co-Author) - Thomas Jefferson University Hospital Department of Radiation Oncology; Lauren Holt, BA (Co-Author) - Drexel University College of Medicine; Sophia Shah (she/her/hers), BS (Co-Author) - Sidney Kimmel Medical College; Hamail Iqbal (he/him/his), BA (Co-Author) - Cooper Medical School of Rowan University; Debanjan Haldar (he/him/his), MD (Co-Author) - Thomas Jefferson University; Gregory Alexander, MD (Co-Author) - Thomas Jefferson University Hospital Department of Radiation Oncology; Wenyin Shi (he/him/his), MD, PhD (Co-Author) - Thomas Jefferson University Hospital Department of Radiation Oncology