Dosimetric Quantification of a Commercial Dual-Tube Kv System for Preclinical Flash Research
Abstract
Purpose
Ultra-high-dose-rate (≥40 Gy/s, UHDR) FLASH radiotherapy (RT) has shown encouraging preclinical normal tissue sparing, with equal tumor control as conventional RT. A kV dual-tube system in parallel-opposed geometry has been proposed as a small-animal FLASH research platform. We improve the dosimetric commissioning of the dual-tube system by addressing the pronounced asymmetry in depth-dose distributions between the tubes, which lead to non-uniform dose delivery along the beam axis. We characterize the time-resolved synchronization of the dual-tubes, critical for quantifying effective dose-rate (DR).
Methods
The dual-tube system is CIX-FLASH (XStrahl), up to nominal 150kVp. The dose-per-pulse is defined as the combined single-pulse output from the two tubes, and DR as dose-per-pulse divided by the pulse length. We used film to measure the output, depth dose, and profile at 5mm increments in solid water and reconstructed full 3D dose distributions. We characterized the pulse synchronization between tubes using a scintillator-based detector with 1-ms resolution.
Results
We showed >20% tube output discrepancies at nominally equal mA/ms settings. We analyzed an in-vivo lung case where naïve dosimetry would result in 20% of the organ receiving >105% of prescribed dose. We devised two corrective strategies – tube output compensation and isocenter shifting – based on dosimetric characterization of each tube. Additionally, we identified 10±7 ms synchronization jitter between pulses from the two tubes. Jitter disproportionately impacts the DR at low dose-per-pulse settings (>15% DR uncertainty at nominal DR ≥ 80 Gy/s for 3–5 Gy per-pulse), while the effect is less pronounced (<5%) at 15 Gy per-pulse. Corresponding QA was designed to monitor tube synchronization over time.
Conclusion
We quantified the impact of asymmetric tube output and tube synchronization on dosimetry and their implications for preclinical studies, such as fractionated studies. The proposed methodology and QA would mitigate or monitor of these effects, ensuring study reproducibility.