Long-Term Analysis of NRG Oncology RTOG 0539: A Phase II Trial of Observation for Low-Risk Meningioma and Radiotherapy for Intermediate- and High-Risk Meningioma

NRG Oncology RTOG 0539 was a prospective phase II trial of risk-adapted radiotherapy for patients with WHO grade 1-3 meningioma. Low-risk (group 1, n = 60) was defined as a grade 1 tumor after gross total resection or subtotal resection (GTR/STR) and prospectively monitored. Intermediate-risk (group 2, n = 52) was defined as recurrent grade 1 or newly diagnosed grade 2 tumor after GTR and treated with radiotherapy (54 Gy). High-risk (group 3, n = 53) included a newly diagnosed grade 2 tumor after STR, newly diagnosed grade 3 tumor, or recurrent grade 2 or 3 tumor and treated with radiotherapy (60 Gy). Progression-free survival (PFS) and overall survival (OS) were estimated using the Kaplan-Meier method. The median follow-up times for the low-, intermediate-, and high-risk cohorts were 12.1, 12.0, and 11.1 years, respectively. The 10-year PFS and OS rates for the low-, intermediate-, and high-risk cohorts were 85.2% and 94.1%, 72.2% and 84.7%, and 42.5% and 51.1%, respectively. Five patients (9.6%) and eight patients (15.1%) had a grade 3+ toxicity attributed to radiotherapy in the intermediate- and high-risk cohorts, respectively. The long-term outcomes using this risk-adapted approach support observation for low-risk patients, inform radiotherapy patient selection and practice standards for intermediate- and high-risk patients, and provide comparative benchmarks for future trials.