KEY POINTS
- The study retrospectively analyzed 18 resected brain metastasis cavities treated with GammaTile brachytherapy. Each implant used 10–32 Cs-131 sources, with a median of 20, embedded at fixed spacing within collagen tiles placed along the surgical bed.
- Investigators evaluated a 5-mm expansion around the resection cavity using standard SFRT metrics. For the at-risk tissue outside the cavity itself, mean doses were D90 56.1 Gy, D50 86.7 Gy, D10 148.8 Gy and D5 175.8 Gy, demonstrating substantial intentional dose heterogeneity.
- Peak-to-valley surrogates were relatively consistent between patients. Mean D10/D90 was 2.7 and D5/D95 was 3.5 in the 5-mm evaluation volume, values broadly overlapping those reported for linac-based lattice RT.
- GammaTile also produced a fixed spatial pattern of high-dose regions. Because every 2 × 2 cm tile contains four equally spaced sources, the high-dose core density remained 1 high-dose core per cm² regardless of implant size.
- The conventional GammaTile prescription of 60 Gy at 5 mm depth closely approximated the observed valley dose: mean D90 was 61.1 Gy when the resection cavity was included and 56.1 Gy when only surrounding at-risk tissue was analyzed.
- Dose heterogeneity remained relatively reproducible despite differences in cavity size, anatomy and number of implanted sources. For the evaluation target, D10/D90 ranged from 2.0 to 3.3 and D5/D95 from 2.3 to 4.6.
- This was a dosimetry study only. It did not evaluate local control, radiation necrosis or normal-brain dose outside the 5-mm target, and similarity to GRID or lattice dosimetry does not establish equivalent biological effects.
CLINICAL TAKEAWAY
GammaTile creates a highly heterogeneous postoperative dose distribution with regularly spaced high-dose peaks and lower-dose valleys, making it dosimetrically similar to established forms of SFRT. Whether this spatial pattern contributes to the clinical outcomes reported with GammaTile remains a biological hypothesis rather than a demonstrated mechanism.