Room: Exhibit Hall | Forum 7
Purpose: To investigate the use of a single quadrupole Halbach cylinders to produce planar proton minibeams suitable for use in proton minibeam radiation therapy (pMBRT)
Methods: Monte Carlo simulations of 118 MeV (9.8 cm range in water) unmodulated proton pencil beams were focused by a single magnet of lengths 68 to 100 mm cm with field gradients of 200 to 250 T/m. Five parallel beams with initial beams diameters ranging from 10 to 15 mm and separated by 4.5 to 6 mm (center to center) were used to create combined dose distributions at Bragg depth. Dose was scored in a voxelized water phantom with voxel size 1.0 mm in beam direction and 0.5 mm x 0.5 mm transversely. Depth dose profiles (DDP) were determined along the axis of the central beam (ie, peak DDP) as well as the parallel axis between the central and an adjacent beam (ie, valley DDP). Transverse profiles were also obtained across the combined distribution from the phantom entrance to Bragg depth.
Results: The combined dose distributions from the five beamlets were highly spatially fractionated in entrance and proximal regions but blended into a homogeneous dose at the target. The peak-to-valley dose ratios were as high as ~27, peak-to-entrance dose ratios of peak DDPs up to ~19, and FWHM of central beamlets at 10 mm WED were as low as ~1.2 mm.
Conclusion: This preliminary data suggests that magnetic focusing in pMBRT can deliver dose distributions that are comparable and potentially superior to those generated using collimators or MLCâ€™s. In addition, the use of collimators can negatively impact dose rate and lead to the production of extraneous secondary particles. Magnetic focusing technology for pMBRT could be applied both in passive and active proton delivery and is the subject of ongoing research.
Funding Support, Disclosures, and Conflict of Interest: This project was supported by funding from the Del Webb Foundation and the Department of Defense (DOD W81XWH-BAA-10-1). There are no conflict of interests to disclose.