Reactor-based boron neutron capture therapy for 44 cases of recurrent and refractory high-grade meningiomas with long-term follow-up

Background. High-grade meningioma (HGM) is difficult to treat, and recurrent HGM after radiotherapy has an especially poor prognosis. We retrospectively analyzed the cases of 44 consecutive patients with recurrent and refractory HGM who were treated by reactor-based boron neutron capture therapy (BNCT). Methods. In 2005-2019, we treated 44 recurrent and refractory HGMs by reactor-based BNCT. We analyzed the patients' tumor shrinkage, overall survival (OS) after initial diagnosis, OS after BNCT, progression-free survival (PFS) post-BNCT, and treatment failure patterns. Results. The median OS (mOS) after BNCT and mOS after initial diagnosis were 29.6 (95% CI: 16.1-40.4) and 98.4 (95% CI: 68.7-169.4) months, respectively. The median follow-up after BNCT was 26 (6.4-103) months. The grade 2 (20 cases) and 3 (24 cases) post-BNCT mOS values were 44.4 (95% CI: 27.4-not determined) and 21.55 (10.6-30.6) months, respectively (P = .0009). Follow-up images were obtained from 36 cases at >3 months post-BNCT; 35 showed tumor shrinkage during the observation period. The post-BNCT median PFS (mPFS) of 36 cases was 13.7 (95% CI: 8.3-28.6) months. The post-BNCT mPFS values in patients with grade 2 and 3 disease were 24.3 (95% CI: 9.8-not determined) and 9.4 (6.3-14.4) months, respectively (P = .0024). Local recurrence was observed in only 22.2% of cases. These results showed good local tumor control and prolonged survival for recurrent HGM cases. Conclusions. Most of these cases had relatively large tumor volumes. The proportion of grade 3 patients was extremely high. Our patients thus seemed to have poor prognoses. Nevertheless, reactor-based BNCT exerted relatively good local control and favorable survival for recurrent and refractory HGMs.