Abstract
BackgroundLaser acceleration of protons and heavy ions may in the future be used in radiation therapy. Laser-driven particle beams are pulsed and ultra high dose rates of >109 Gy s-1may be achieved. Here we compare the radiobiological effects of pulsed and continuous proton beams.MethodsThe ion microbeam SNAKE at the Munich tandem accelerator was used to directly compare a pulsed and a continuous 20 MeV proton beam, which delivered a dose of 3 Gy to a HeLa cell monolayer within < 1 ns or 100 ms, respectively. Investigated endpoints were G2 phase cell cycle arrest, apoptosis, and colony formation.ResultsAt 10 h after pulsed irradiation, the fraction of G2 cells was significantly lower than after irradiation with the continuous beam, while all other endpoints including colony formation were not significantly different. We determined the relative biological effectiveness (RBE) for pulsed and continuous proton beams relative to x-irradiation as 0.91 ± 0.26 and 0.86 ± 0.33 (mean and SD), respectively.ConclusionsAt the dose rates investigated here, which are expected to correspond to those in radiation therapy using laser-driven particles, the RBE of the pulsed and the (conventional) continuous irradiation mode do not differ significantly.
Highlights
Laser acceleration of protons and heavy ions may in the future be used in radiation therapy
With respect to potential differences in the radiobiological effects of laser-accelerated particles and those accelerated conventionally by cyclotrons or synchrotrons, the main difference is that particle beams delivered from laser acceleration will be pulsed
While the laser pulses required for the acceleration of high energy particles are in the range of femtoseconds, the particle pulse created will spread in time during beam transport
Summary
Laser acceleration of protons and heavy ions may in the future be used in radiation therapy. Laserdriven particle beams are pulsed and ultra high dose rates of >109 Gy s-1may be achieved. While the laser pulses required for the acceleration of high energy particles are in the range of femtoseconds, the particle pulse created will spread in time during beam transport. Assuming protons with a mean energy of 100 MeV and an energy spread of 1% which are transported over a 20 m distance, the expected duration of the pulse at the target will be about 1 ns [11]. Since the repetition rates of laser accelerators are expected to be rather moderate, one can envision that during one session each voxel of the PTV (planning treatment volume) can be targeted at most a few times if the treatment duration is to be kept reasonably short. Assuming a deposition of >1 Gy in 1 ns, this translates to an ultra high dose rate of >109 Gy s-1
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