Region-Aware Boundary-Weighted Dice Does Not Resolve the Core–Enhancing Trade-off in Brain Tumor Segmentation: A Controlled Negative Result on BraTS 2020

S.U. Ravi Kumar Chavali; V. Kumar P.

doi:10.62127/aijmr.2026.v04i04.1463

Region-Aware Boundary-Weighted Dice Does Not Resolve the Core–Enhancing Trade-off in Brain Tumor Segmentation: A Controlled Negative Result on BraTS 2020

Author(s)	Mr. S.U. Ravi Kumar Chavali, Dr. V. Kumar P.
Country	India
Abstract	A companion matched-condition study found that a boundary-weighted Dice loss (BW-Dice) improves tumor-core (TC) segmentation but degrades enhancing-tumor (ET) segmentation — a trade-off with no net gain — and hypothesized a scale-mismatch mechanism in which the boundary-emphasis kernel is wider than the small ET region. We test the natural prediction of that hypothesis: shielding ET from the boundary emphasis should preserve the TC gain while removing the ET loss. Under matched conditions on BraTS 2020, we train a region-aware BW-Dice variant that applies boundary weighting to the necrotic-core and edema channels but trains ET with standard Dice, evaluated across three random seeds, a kernel-width sweep, and two additional decoders. Region-aware weighting does not improve on BW-Dice: in numerically stable settings it is equal to or worse than BW-Dice on both TC and ET, and a single-seed apparent gain proves non-reproducible. The core–enhancing trade-off is therefore not a fixable artifact of kernel scale. We also document seed- and architecture-dependent mixed-precision instability of weighted-Dice losses. Reporting this negative result narrows the space of promising loss-design interventions.
Keywords	Brain tumor segmentation; BraTS 2020; boundary-weighted loss; negative result; reproducibility
Discipline	Computer > AI / ML
Published In	Volume 4, Issue 4, July-August 2026
Published On	2026-08-15
DOI	https://doi.org/10.62127/aijmr.2026.v04i04.1463

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Region-Aware Boundary-Weighted Dice Does Not Resolve the Core–Enhancing Trade-off in Brain Tumor Segmentation: A Controlled Negative Result on BraTS 2020

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