A novel dosimetry system for three-dimensional dose distribution characterization of proton pencil beams

Efficient and accurate measurement methods to acquire three-dimensional (3D) dose distributions of proton pencil beams are currently lacking. Conventional dosimetric techniques demonstrate limitations in achieving spatially complete and metrologically precise rapid 3D dose measurements, which reduces the accuracy of beam modeling in treatment planning system (TPS) and the efficiency of routine quality assurance (QA) practices.

To develop an efficient and accurate dosimetry system for 3D dose distribution characterization of proton pencil beams.

We developed a newly designed 3D dosimetry system (PBDOSEmini), which integrates two multi-strip ionization chambers (MSICs), a servo motor system, and a sealed water tank. To achieve rapid and precise measurement of 3D dose distributions, this system employs continuous dynamic scanning combined with dual-detector synchronized measurement technology. In a clinical proton beamline, the spatial and dosimetric performances of the PBDOSEmini were characterized and compared with Monte Carlo simulation results, as well as measurements using Gafchromic films (EBT3) and a commercial water phantom system (IBA Blue Phantom²).

The PBDOSEmini demonstrated a linearity of R² > 0.999 for both dose and dose rate within the clinical range. The 2D dose comparison to the film measurement resulted in a position deviation less than 0.5 mm and a size deviation of beam spot less than 3%. A 3D dose distribution measured within 30 seconds was compared to simulation results and showed an average gamma passing rate of 96.13% (2 mm/2%). Comparative analysis indicates acceptable agreement between the measured depth-dose distributions from PBDOSEmini and Blue Phantom². Repeatability verification showed that the median relative standard deviation (RSD) of all data points was 0.17% (IQR = 0.04%).

The newly designed PBDOSEmini demonstrates excellent spatial and dosimetric performance, making it highly suitable for providing fundamental data for TPS, routine QA practices, and other clinical applications in proton therapy.