INNV-26. FEASIBILITY EVALUATION OF TUMOR TREATING FIELDS (TTFIELDS) THERAPY FOR BRAINSTEM GLIOMAS

Abstract BACKGROUND Tumor Treating Fields (TTFields) therapy is a novel anti-mitotic therapy that is FDA-approved for use in patients with newly diagnosed and recurrent glioblastoma (GBM). However, TTFields therapy is currently only approved for supratentorial GBM, and the feasibility of TTFields therapy for treating infratentorial GBM remains unknown. TTFields values of average local minimum power density (LMiPD) >1.15 mW/cm3 and local minimum field intensity (LMiFI) >1.06 V/cm, were associated with improved OS and PFS based on a posthoc analysis of the EF-14 study. This is a dosimetric planning evaluation of the feasibility of TTFields therapy for brainstem gliomas. METHODS MRIs of patients with brainstem gliomas were used for this dosimetric evaluation, with planning conducted using MAXPOINT (Novocure, Switzerland). Gross tumor volume (GTV) for TTFields planning was defined as enhancing tumor on T1 post contrast MRI. Clinical target volume (CTV) was defined as GTV expanded by a 3 mm margin around sum total of resection cavity, necrotic core, and enhancing tumor. LMiPD and LMiFI to the GTV and CTV were evaluated. RESULTS A total of 5 patients with brainstem gliomas were included in this study. The median GTV volume was 8.2 cc (range: 3.8 – 13.5 cc), and median CTV volume was 18.6 cc (range: 9.1 – 23.4 cc). The median LMiPD for GTV and CTV were 1.9 (range: 1.1 – 2) and 1.9 (range: 1-2.1) mW/cm3, respectively. The median LMiFI for GTV and CTV were 1.3 (range: 1.1-1.6) and 1.2 (range: 1.1-1.6) V/cm, respectively. CONCLUSION LMiPD and LMiFI values for brainstem gliomas achieved levels that are consistent with those associated with improved OS and PFS in posthoc analyses in supratentorial GBM. This dosimetric planning study suggests feasibility and theoretical benefit of TTFields for brainstem gliomas. Further clinical evaluation is warranted to validate its efficacy.