Purpose: The current beam configuration use the transition mode of proton Flash beam to irradiate treatment targets. This practice is dictated by the limited capability to the current proton therapy systems to deliver Flash dose-rate over clinically sufficient beam range span. In this study, we investigate the dependency of achievable dose-rate to the main beam parameters for the cyclotron based proton therapy systems.
Methods: The achievable dose-rate versus the beam energy, the beamline transmission efficiency and the cyclotron’s beam current were computed. The beam energy is varied between 70 MeV to 250 MeV (1 MeV step-size), the beamline efficiency is varied from one-tenth to ten folds of the typical beamline transmission at any given proton beam energy. The calculations are repeated for a set of cyclotron beam currents ranging from 100 nA to 1000 nA (100 nA step-size). The maximum achievable dose-rate by the various designs of the commonly used clinical proton therapy systems is indicated thereafter.
Results: Based on our simulation, the maximum achievable dose-rate is 1080 Gy/sec at the beam of 250 MeV where the machine’s beamline transmission efficiency is about 100% and with cyclotron current of 1 µA. For other beam energies, the dose-rate value strongly depends on the beamline transmission efficiency, which varies in average between 10% (high energy) to 0.05% (low energy). In this case, the maximum achievable integral dose-rate is about 110 Gy/sec for 249 MeV and the lowest achievable Flash dose-rate (40 Gy/sec) occurs at the beam energies between 102 MeV and 226 MeV depending on every machine specific beamline transmission efficiency.
Conclusion: We developed an open source calculator for achievable proton Flash dose-rate with input parameters that can be made specific to any cyclotron based proton therapy facility.