Cs-131 Intracavitary Brachytherapy as an Adjunct to Maximal Safe Resection for Locally Recurrent High-Grade Glioma

Brachytherapy as a component of therapy for high-grade glioma (HGG) has generated renewed interest with recent development of a novel Cs-131 seed-based delivery system. We report on the safety and feasibility of maximum safe re-resection (MSR) and intracavitary installation Cs-131 seeds in recurrent glioblastoma. Between January 2019 and December 2019, 10 patients ranging in age from 36-73 (median 57 years) with the diagnosis of recurrent HGG were treated with a combination of MSR followed by the permanent installation of brachytherapy sources. The Cs-131 sources were embedded in an absorbable collagen tile with each tile containing 4 seeds. All had previously received standard surgery and chemoradiation. Nine of the 10 had received at least one additional prior salvage treatment. Gross total re-resection as judged by the neurosurgeon was accomplished in 8 of the 10. A median of 24 seeds (range 6 to 44) were implanted along the cavity wall resulting in a dose of 60 Gy to 5 mm depth. An HRCTV was defined as the cavity wall plus residual enhancement presumed to represent residual tumor. The 30-day operative mortality was 10%. Thirty percent of patients requiring prolonged steroid therapy (> 14 days) after implantation and only 10% of patients requiring prolonged antiepileptic pharmacotherapy (>5 days). One patient died owing to operative hemorrhage resultant from a pre-existing coagulopathy. One patient developed intractable seizures for days. Six patients (60%) had preservation of functional status as defined by less than a 20-point decrease in KPS at 2 months. Local control was challenging to prove, as pseudoprogression was suspected in 2 of the 10 patients (neither of which were MGMT methylated). The median progression free survival was 2.7 months (range: 0.9 to 5.9 months) as defined by the initiation of the next line of therapy. There was no symptomatic radionecrosis noted within our cohort. At time of reporting, 6 of the 10 patients have experienced treatment failure, 1 patient with an in-field failure (defined as within the 90% isodose volume, 1 patient with a distant failure to the radiation volume (defined as beyond the 10% isodose volume), 3 patients with marginal failures (defined between the 90% and 10% isodose lines), and 1 patient with a synchronous marginal and distant failure. High quality implantation was achieved with 7 of 10 patients undergoing brachytherapy implantation in which the HRCTV D90 > 90% (54Gy). The remainder did not meet this quality metric due to anatomic challenges of resectability. Cs-131 seed implantation using a bioabsorbable collagen matrix delivery device is a feasible method of achieving dose-escalated re-irradiation starting at time of implantation.