A Comprehensive Comparative Study of Proton Flash Techniques for Conformal Pencil Beam Scanning Radiotherapy: Pristine Bragg Peak Vs. Spread-out Bragg Peak
Abstract
Purpose
The spread-out Bragg peak (SOBP) technique uses ridge filters to broaden the depth-dose profile, producing a dose distribution similar to a single-field-uniform(SFU) approach. In contrast, the single-energy pristine Bragg peak(SEPBP) approach relies on range compensation and multi-field-optimization (MFO) to enable distal tracking, yielding an IMPT-like dose. Although both techniques have been widely studied across multiple anatomical sites, head-to-head evaluations of their dose and dose-rate remain limited and have not been systematically reported.
Methods
Both FLASH-technique-SEBP using range shifter and range compensators, and SOBP using mini-ridge filters were implemented an in-house planning sytem. A fast monte carlo dose MC2 calculation engine was used for high accuracy dose calculation for the submillimeter pin-shaped mini-ridge filter. To examine physical attributes, a C-shaped target was planned using these strategies maintaining similar minimum-monitor-units and beam configurations. The dosimetric properties compared included 3D dose distribution, uniformity, conformity index(CI), DVHs, and coverage at ultra-high dose rates.
Results
Both the SOBP and SEPBP techniques met all clinical standards, with SEPBP showing a slightly lower maximum dose of 17.15Gy(114.0%) versus 17.27Gy(115%) for SOBP, though not clinically significant. Each plan achieved adequate coverage with ≥95% of the target receiving at least 99% of the prescription. The CI was similar between SOBP(0.99) and SEPBP(1.20), with no clinically significant difference. While DVHs were comparable, SEPBP had greater heterogeneity and dose spillage, affecting a larger volume with lower dose. With 400MMU, the SEPBP method was able to achieve FLASH ratios whereas the SOBP method was unable to. SEPBP showed a more heterogeneous dose rate distribution, particularly at very high dose rates compared to SOBP.
Conclusion
Both methods yield comparable, clinically acceptable dosimetric profiles. However, the SEPBP approach produces higher dose-rate distributions under the same beam parameters due to intrinsic characteristics of the pristine Bragg peak, potentially enabling treatment of larger field sizes.