ESTRO 2024 - Abstract Book

S3366

Physics - Detectors, dose measurement and phantoms

ESTRO 2024

minibeam RT (pMBRT) is a synergy of proton and minibeam. While the single-gantry proton facility has become increasingly popular due to its affordability and compact design, it generally has limited beam time for research. On the other hand, given the current requirement of pMBRT on specific minibeam hardware collimators, a reproducible and fast setup is also desirable to minimize pMBRT treatment time and the switching time between pMBRT and conventional treatment, to clinically translate pMBRT. The contribution of this work is the development and commissioning of the first pMBRT system for single-gantry proton facility, which allows for efficient and reproducible plug-and-play setup within minutes.

Material/Methods:

The single room pMBRT system is constructed based on IBA Proteus®ONE proton machine. The end of nozzle is attached with beam modifying accessories though an accessory drawer. A snout is attached to the accessory drawer and used to hold apertures and range shifters. The snout can be moved in and out of the beam line direction, and the aperture air gap to the phantom is adjusted via snout position adjustment. Since clinical single-room unit does not have a dedicated beam line for research, the ideal pMBRT collimator design should facilitate efficient, reproducible setup, as well as accommodating flexible minibeam patterns. The minibeam aperture uses the aperture slot of the small snout. We split the design into two components, a fitting ring, and an aperture body. The separation of the adapter ring and the aperture body serves two purposes. First, the aperture body now can accommodate various minibeam design and thickness. It reduces the complexity of machining because the creation of the minibeam pattern can be done on simple geometry. Second, the placement of aperture body allows additional freedom to fine tune the leveling of the aperture with respect to the proton beam axis. The central aperture body is 11.5 x 11.5 cm 2 square, and has a thickness of 6 cm.

Results:

The system is validated by film Measurement benchmarked with Monte Carlo (MC) simulation. EBT4-XD film was placed at the phantom surface to be irradiated with a uniform 5cm x 1.5cm field with 150 MeV mono-energy protons. The slit cutting has some intrinsic error tolerance (10% tolerance specified to the vendor) and the lower peak dose on the right side most lateral slit (Slit 5) was 16% lower than the rest of the peaks, likely due to the machining defect. The rest of the peaks had the maximum difference of 4% (Slit 1, 18.1 Gy for simulation, and 17.3 for measurement), and lowest of 2% (Slit 3, 18.7 Gy for simulation, and 18.5 for measurement). The valley dose had the maximum difference of 11% (2.7 Gy for simulation, and 3.2 for measurement). The average dose over the middle three peak-alley region as indicated by the arrow area (Figure 4D), was 7.1 Gy for measurement, and 6.9 Gy for MC, making it to be 3% difference in average dose.