KEY POINTS
- This narrative review examines modern internal radiotherapy for glioblastoma, focusing on its biological rationale, available delivery platforms, radionuclide selection, and the absence of standardized dosimetric frameworks.
- More than 80% of glioblastoma recurrences in several clinical series arise at or near the resection cavity. Brachytherapy is therefore proposed as a complement to external-beam radiotherapy that can deliver immediate dose intensification to the region with the highest residual tumour-cell density.
- Clinically developed intracavitary systems include GliaSite, which used liquid iodine-125 within an inflatable balloon, and GammaTile, which incorporates cesium-131 seeds into a bioresorbable collagen matrix placed along the resection cavity during surgery. Emerging injectable approaches include radionuclide-loaded hydrogels such as holmium-166 chitosan.
- Radionuclide range must be matched to the intended biological target. Alpha particles travel approximately 40–100 μm, Auger electrons less than 100 nm, while beta particles provide millimetre-to-centimetre penetration that may better cover infiltrative disease beyond the immediate cavity wall.
- Device geometry can be as important as radionuclide selection. Liquid balloon sources generate comparatively spherical dose distributions, whereas discrete seed matrices produce heterogeneous gradients around individual sources; hydrogel systems may conform more closely to irregular three-dimensional cavities.
- The authors identify dosimetry as the central translational barrier. Conventional TG-43 calculations assume homogeneous water-equivalent tissue, whereas model-based approaches and Monte Carlo simulations can account for cavity geometry, tissue composition, implant materials, radioactive decay, and evolving postoperative anatomy.
- Current evidence does not establish brachytherapy as a replacement for standard external-beam radiotherapy and temozolomide. Comparative efficacy, neurotoxicity, radionuclide-specific biological effects, patient selection, procedural standardization, and health-system implementation all remain insufficiently defined.
CLINICAL TAKEAWAY
Intracavitary brachytherapy directly addresses the dominant pericavitary failure pattern of glioblastoma and may shorten the untreated interval after surgery. Its broader role remains investigational, and progress depends on standardized dosimetry and prospective comparisons rather than further device innovation alone.