F. Ehret, G. Lee, K. S. Oh, M. R. Bussiere, and H. A. Shih; Department of Radiation Oncology, Massachusetts General Hospital and Harvard Medical School, Boston, MA
Purpose/Objective(s): Grade 2 meningiomas often recur after surgery and radiotherapy. Refinement of local treatment options requires an understanding of their limitations. Herein, we report the results of a pattern-of-failure analysis of patients with grade 2 meningiomas treated at a large tertiary center with proton or photon-based fractionated radiotherapy.Materials/
Methods: Patients with progressive or recurrent grade 2 meningioma by the WHO 2021 tumor classification who underwent initial radiotherapy between 2000 and 2023 were analyzed. Adjuvant (received radiotherapy after surgery) and salvage treatments with proton or photon-based fractionated radiotherapy were assessed. All cases had a confirmed tumor progression during the available follow-up. Imaging data demonstrating recurrence was overlaid with the initial treatment plan for pattern-of-failure analysis. Results: One hundred forty-two patients with a grade 2 meningioma underwent fractionated radiotherapy during this period. There were 36 confirmed tumor progressions or recurrences with available imaging and treatment plans. The median radiographic and clinical follow-up periods for these patients were 81.0 and 83.3 months, respectively. Most tumors were located along the convexity (n = 18, 50.0%) and near the skull base (n = 10, 27.8%) at initial resection. Among these cases, 22 (61.1%) patients had an initial subtotal resection (STR), while the remaining 14 (38.9%) had a gross total resection (GTR). Thirteen patients (36.1%) had received adjuvant radiotherapy, and 23 patients (63.9%) had received salvage radiotherapy. The median prescription dose for the entire cohort was 59.4 Gy (range 37.5 – 63 Gy), with 21 patients (58.3%) receiving proton radiotherapy. The median time to progression was 48.8 months, and patients who received salvage vs. adjuvant radiotherapy had shorter median times to progression (39.8 vs. 76.9 months). The median times to progression or recurrence following GTR and STR did not differ (45.0 vs. 48.8 months). There were no differences in the time to failure between patients receiving = 59.4 Gy (n = 25, 69.4%) or < 59.4 Gy (n = 11, 30.6%). The median recurrence volume was 1.79 cc. Locations of tumor progression were as follows: 7 (19.4%) exclusively occurring in the targeted volumes and 7 (19.4%) exclusively outside the targeted volume. Most recurrences and progressions (n = 20, 55.6%) involved all target volumes and had at least some tumor growth beyond the targeted volume. Conclusion: In this cohort, tumor progressions and recurrences of grade 2 meningiomas after adjuvant or salvage radiotherapy primarily occurred in close spatial relation to the irradiated volume, with only a minor proportion of distant failures, underlining the need for further treatment refinements to prevent local failure. Further in-depth analyses on the spatial dose distribution, target delineation, and tumor recurrence are pending.
