Combining proton FLASH and spatially fractionated radiotherapy: experimental and simulation-based dosimetric...

Area of Science:

• Radiation Oncology
• Medical Physics
• Biomedical Engineering

Background:

• Ultra-high dose rate (UHDR) proton therapy and spatially fractionated radiotherapy (SFRT) are advanced techniques for improved tumor control and normal tissue sparing.
• Integrating UHDR proton therapy with SFRT may offer synergistic benefits, but practical implementation requires further research.

Purpose of the Study:

• To develop and validate a Monte Carlo (MC) simulation framework for designing multi-slot collimators to generate planar minibeams (PMBs) under UHDR conditions.
• To explore the integration of UHDR proton therapy with SFRT for enhanced tumor control and minimized normal tissue damage.

Main Methods:

• A tungsten alloy multi-slit collimator was designed to produce PMBs (508-micron width, 1524-micron center-to-center spacing).
• Dosimetric characterization was performed using a 250 MeV UHDR-capable proton beam, measuring dose distributions in solid water phantoms.
• TOPAS MC toolkit was used to model collimator configurations, validating measurements and evaluating designs for preclinical UHDR-SFRT studies.

Main Results:

• The prototype collimator successfully generated PMBs at 250 MeV with UHDR dose rates (peak 179.3 Gy/s, valley 82 Gy/s).
• Measured depth of convergence was 80 mm with a peak-to-valley dose ratio (PVDR) of 1.8.
• MC simulations closely matched experimental data (RMSPE < 4.50%), and alternative designs showed reduced PVDR with closer spacing.

Conclusions:

• The study confirms the feasibility of combining UHDR proton therapy and SFRT using a 250 MeV proton beam.
• The validated MC simulation framework provides a powerful tool for designing and optimizing collimators for UHDR-SFRT applications.