Author: Gulakhshan M Hamad, Sina Mossahebi, Yannick P. Poirier, Amit Sawant 👨🔬
Affiliation: University of Maryland School of Medicine, Maryland University Baltimore 🌍
Purpose:
The combination of ultra-high dose rate (UHDR) proton therapy, known for normal tissue sparing, with spatially-fractionated radiotherapy (SFRT), promising enhanced tumor control and tissue sparing, offers a compelling therapeutic approach. UHDR minibeams, created by multi-slit collimators, can deliver targeted treatment while preserving healthy tissues. This study validates Monte Carlo (MC) simulations for dosimetric characterization of a collimator generating planar proton minibeams (PMBs) and informs optimized collimator designs for preclinical studies.
Methods:
A 4 cm-thick tungsten alloy multi-slit collimator was designed to generate PMBs with a 508-micron width and 1524-micron center-to-center spacing. Dosimetric characterization was performed using 250MeV on a Varian ProBeam system, the highest energy suitable for producing UHDR minibeams. Planar and depth dose distributions were measured using Gafchromic EBT-XD film in solid water phantoms. Key Dosimetric measures, including depth of convergence and peak-to-valley dose ratio (PVDR), were quantified. The beam characteristics of were specified using the TOPAS MC toolkit. Simulations were performed to validate experimental data and then used to optimize collimator design for preclinical tumor study.
Results:
The collimator successfully produced planar PMBs. Experimental measurements and simulations demonstrated excellent agreement, confirming the feasibility of generating UHDR minibeams with the designed collimator. At 250 MeV, dose rates suitable for UHDR irradiations were achieved, with a dose rate of 30 Gy/s. The depth of convergence was at 80 mm, and a PVDR of 1.8 was characterized, providing insight into the collimator’s performance and its optimization for preclinical studies.
Conclusion:
This study demonstrates the technical feasibility of combining UHDR and SFRT at 250MeV proton beam, highlighting its potential for clinical translation. Our MC simulation framework enables us and others to design and optimize collimators (beyond current scope) for a variety of preclinical applications.