Electron spatially fractionated radiation therapy using a clinically biocompatible 3D-printed tungsten-filament GRID
Melody Liu1, Zhengzheng Xu1, Hualin Zhang1
1Department of Radiation Oncology, Norris Comprehensive Cancer Center, University of Southern California Keck School of Medicine, Los Angeles, California, USA.
Background:
Spatially fractionated radiation therapy (SFRT) can enhance tumor control by delivering high-dose subvolumes while sparing normal tissue and stimulating antitumor immunity. However, its application to superficial disease through electron beam radiation therapy remains limited. Electron SFRT (eSFRT) could serve as a strategy for initial tumor downsizing of ulcerated cutaneous and subcutaneous tumors by delivering a superficial, spatially heterogeneous dose, enabling subsequent conventional electron therapy to enhance local control.
Purpose:
To evaluate the dosimetric feasibility of eSFRT using a novel 3D-printed tungsten-filament GRID (TS) and compare it to lead sheet (LS) references.
Methods:
The TS GRID collimators were 3D-printed from a tungsten alloy filament (91%-93% tungsten by weight, PLA-based), with a hexagonal array of 27 apertures (1.5 cm diameter, 2.0 cm spacing, 1 mm thickness) in a 10 × 10 cm2 sheet. LS GRIDs (1.5 and 3.0 mm thick) were used as reference. GRIDs were placed directly on water and anthropomorphic phantoms. Dosimetric measurements for GRID field properties, including percent depth dose (PDD) and crossbeam plane dose profiles at various depths, were performed in a water tank phantom for 6, 9, and 12 MeV electron beams. Key parameters, such as depths of maximum dose (dmax) and doses at 90% (d90) and 50% (d50), were determined. Peak-to-valley dose ratios (PVDRs) were also evaluated and compared with data from an anthropomorphic phantom.
Results:
The TS GRID collimator produced highly heterogeneous superficial dose distributions with PVDR > 2.0 at depths > 10 mm for 6-9 MeV, supporting spatially fractionated dose delivery. PVDR reductions on curved phantom surfaces were minimal (<3%). TS demonstrated reproducible geometry, mechanical stability, and biocompatibility, enabling direct placement on superficial tumors. Compared to previously reported tungsten-based composite GRID collimators, including tungsten functional paper (TFP) and tungsten-containing rubber (TCR), TS achieved higher PVDR at clinically relevant depths. LS GRID collimators achieved slightly higher PVDR but are not suitable for clinical use directly on skin.
Conclusions:
This study demonstrates the feasibility of eSFRT using a 3D-printed TS GRID collimator to deliver superficial, spatially heterogeneous doses. TS provides reproducible geometry, mechanical stability, and biocompatibility, making it a clinically translatable alternative to lead, TFP, and TCR GRID collimators warranting further preclinical and clinical investigation.
