Patient-Specific Segmentation-Based Treatment Planning vs NovoTAL for Tumor Treating Fields Therapy in Glioblastoma

Summary: Purpose: Patients treated with Tumor Treating Fields (TTFields) therapy for glioblastoma (GBM) have array layouts planned by NovoTAL. NovoTAL requires morphometric inputs and maximizes field intensity at the tumor. Patient-specific segmentation-based treatment planning (SBTP) software maximizes local minimum power density (LMiPD; mW/cm3) at a defined primary region of interest (ROI). This retrospective simulated testing compared calculated LMiPD and local minimum field intensity (LMiFI; V/cm) to ROIs with SBTP vs NovoTAL layouts. Methodology: 37 patients from 5 sites who received TTFields therapy for GBM using NovoTAL were included. Treatment plans using prescribed/treated NovoTAL layouts and de novo SBTP layouts optimized to CTV were created with SBTP. Three ROIs representing the original treated GBM (CTV), high risk margin around the GBM (CTV-2), and recurrent GBM (CTV-R) were created. Layout rankings based on LMiPD, average LMiPD and LMiFI, D95, D5, DVHs, and voxel-by-voxel percentages based on LMiPD were compared between SBTP vs NovoTAL layouts (paired t-tests). Results: Average LMiPD (1.551 vs 1.194) and LMiFI (1.115 vs 0.978) to CTV were significantly higher with SBTP vs NovoTAL (P<0.0001 for each). Average LMiPD (1.445 vs 1.164) and LMiFI (1.197 vs 1.077) to CTV-2 were also higher (P<0.0001 for each). There was a positive trend to higher average LMiPD (1.203 vs 1.157; P=0.212) and LMiFI (1.103 vs 1.090; P=0.311) to CTV-R. Top ranked overall layouts by LMiPD to CTV were SBTP layouts (97%; 36/37). Percent ratio ([SBTP-NovoTAL]/NovoTAL*100) D95 for LMiPD was 49% (to CTV), 29% (to CTV-2), and 12% (to CTV-R) and for LMiFI was 20%, 13%, and 5%, respectively. Percent ratio D5 for LMiPD was 32%, 26%, and 7% and for LMiFI was 14%, 10%, and 1%, respectively. For a given percent CTV volume, minimum LMiPD and LMiFI were higher with SBTP (95%, 35/37; DVH curves shifted to right). SBTP yielded higher LMiPD to the majority of voxels within the CTV (95%, 35/37). With SBTP, LMiPD to CTV was significantly higher than to CTV-R (P<0.001). Conclusions: These retrospective simulated data suggest that layouts generated by both SBTP and NovoTAL meet or exceed the established treatment threshold for TTFields therapy (1). SBTP yielded higher calculated LMiPD and LMiFI, D95, D5, and percent voxel LMiPD to defined ROIs. Higher LMiPD to CTV vs CTV-R with SBTP suggests a potential benefit to re-planning if GBM recurs. Given previous reports showing that higher LMiPD and LMiFI are positively correlated with improved overall and progression free survival (2), patient-specific SBTP may potentially lead to improved clinical outcomes for patients with GBM.