Clinical commissioning of a commercial brass GRID collimator for spatially fractionated radiotherapy.

Spatially Fractionated Radiation Therapy (SFRT) delivers high-dose radiation in a GRID pattern to treat large tumors. This can be achieved using either a physical GRID block or virtual MLC-based patterns. This report presents our experience commissioning a commercial brass GRID collimator for SFRT. Commissioning was performed using a brass GRID collimator with 6 MV and 10 MV photon beams under both flattening filter (FF) and flattening filter-free (FFF) configurations. Dosimetric measurements were collected in a water phantom and compared with treatment planning system calculations. SFRT test plans were created and validated using a commercial detector array. Valley-to-peak dose ratio (VPDR) ranged from 0.20 to 0.30 (6-MV) and 0.30 to 0.37 (10-MV). The Percent depth doses were lower than those for open fields at all beam energies. Measured vs. calculated profiles agreed within ±5% in dose and 1 mm in distance for all beam energies. TPS-generated plans showed strong agreement with measured distributions, with an average gamma passing rate of 96.5% (3%/3 mm criteria). We successfully commissioned and validated a commercial GRID collimator for SFRT using 6-MV and 10-MV photon beams in both FF and FFF modes. Despite its substantial weight and limited maximum field size of 25 × 25 cm², GRID-based SFRT offers straightforward treatment planning, efficient dose delivery, and the potential to enhance tumor control through its characteristic peak-to-valley dose distribution.