Analysis of patterns of failure and appraisal of postoperative radiation field for grade II–III meningioma

Purpose: To analyze patterns of failure according to treatment modalities and evaluate the adequacy of an institution’s current volume of postoperative radiotherapy (PORT) for World Health Organization (WHO) grade II or III meningiomas. Patients and methods: Data of 98 patients treated by either surgery and PORT (PORT group, n = 53) or surgery alone (surgery group, n = 45) between March 2000 and December 2013 were reviewed. Clinical target volume of PORT was delineated as a 1.5–2-cm expansion from the tumor bed. Local failure (LF) was defined as recurrence within a 2-cm margin from the tumor bed. Failures other than LF were defined as out-field failure (OFF). Median total dose of PORT was 59.4 (range 45.0–69.0) Gy. Results: The PORT group had larger proportions of grade III meningiomas (18/53, 34.0%) than the surgery group (8/46, 15.6%) (p = 0.037). After a median 73.4-month follow-up, 29 patients experienced LF and 5 developed OFF. The actuarial 5-year local control (LC) rates were 86.7% and 59.3% in the PORT and surgery groups, respectively (p = 0.002). PORT was a significant factor of LC in the univariate (p = 0.003, hazard ratio [HR] 3.449, 95% confidence interval [CI] 1.516–7.846) and multivariate analyses (p < 0.001, HR 5.486, 95% CI 2.178–13.820). Conclusions: Despite the larger proportion of grade III meningiomas in the PORT group, PORT reduced LF in patients with WHO grade II or III meningiomas compared with the surgery group. The current PORT field seems reasonable because LF was the dominant pattern of failure in patients treated by surgery alone.