Presenter(s)
B. Pawalowski1, M. Kruszyna- Mochalska1,2, M. Wosicki1, T. G. Piotrowski1,2, and J. Malicki2,3; 1Department of Medical Physics, Greater Poland Cancer Centre, Poznan, Poland, 2Department of Electroradiology, Poznan University of Medical Sciences, Poznan, Poland, 3Greater Poland Cancer Centre, Poznan, Poland
Purpose/Objective(s):
Delivering FLASH treatments within <200 ms is widely considered a critical requirement to preserve the intended ultra-high dose-rate exposure conditions associated with the FLASH effect. We assessed whether a novel UHDR electron accelerator can deliver a clinically relevant dose accurately and reproducibly across a broad range of pulse-structure settings (different pulse widths and pulse repetition frequencies) while maintaining FLASH-relevant short delivery times.
Materials/Methods:
Electron beams at 6 and 9 MeV were delivered with switchable pulse-time structure: using pulse widths: 1.5 - 4.4 µs and pulse repetition frequencies (PRF): 50–300 Hz. Firstly, the dose per pulse for each pulse width setting was measured using an active diamond detector in a fixed geometry. Afterwards, number of pulses from 2 to 15 was pre-set to obtain total dose of 5 Gy. The delivered dose was then measured and compared with the pre-set dose.
Results:
Dose per pulse depended on pulse-time structure but was reproducible within each setting (6 MeV: 0.342–2.056 Gy/pulse; 9 MeV: 0.501–2.890 Gy/pulse). Across all tested configurations, agreement between pre-set and measured dose was within ±1.78% (6 MeV) and ±1.38% (9 MeV), demonstrating consistent dose delivery despite large changes in pulse-time structure. For pulse-time structures with very high doses per pulse, obtaining exactly 5 Gy was not always possible because the dose could only be adjusted in discrete one-pulse steps therefore, the closest attainable dose was pre-set. For example, at 6 MeV with t=4.4 µs, the nearest dose to 5 Gy was 4.112 Gy (N=2). At fixed pulse width and pulse count, while changing PRF from 50 to 300 Hz it resulted with the least dose variation for 6 MeV (~0.5%) and small variation for 9 MeV (~1.5%), showing near-independence of the delivered dose over the tested range. Time of delivery 5 Gy were completed within 10–200 ms for PRF =100 Hz; at 300 Hz, same deliveries required 6.7–26.7 ms.
Conclusion:
The novel UHDR platform enables highly reproducible dose delivery across a wide range of pulse-width and PRF configurations up to 300 Hz, verified with a diamond detector, while maintaining FLASH-critical treatment times <200 ms. Importantly, higher dose per pulse (fewer pulses) complicated precise dose targeting, in contrast, lower dose per pulse combined with higher PRF provided finer dose resolution, improved dose controllability, and still enabled pre-set dose delivery below 200 ms.
