Laser Generated Proton Beams for Hadron TherapyChristopher Hughes1, Oliver Ettlinger1, Jonathan Bryanti1, Saleh Alatabi1

1Imperial College London, Blackett Lab, Prince Consort Road, London, United Kingdom

Ion Acceleration via Hole-boring

References

Ion Beam Delivery to Patient

At high intensities, the laser radiation pressure (RP) can be greater than the thermal pressure of a plasma. the critical density surface is driven spatially into the plasma at a velocity known as the Hole-Boring (HB) velocity, vHB.

The ions ‘bounce’ off this front and are accelerated – favourable energy scaling.

The Current State of Hadron TherapyHadron therapy uses charged particles to treat deep-seated tumours while delivering lower radiation dose to neighbouring tissue due to its Bragg peak characteristic.

Hadron therapy facilities use RF accelerators which are large and expensive.

[4] http://ccpforge.cse.rl.ac.uk/gf/project/epoch/[5] D. Gabor, Nature 159, (1947)[6] J. Pozimski and M. Aslaninejad, Laser and Particle Beams, 31, (2013) [7] Yogo, A. et al. Appl. Phys. Lett. 98, 053701 (2011)

Two-dimensional particle-in-cell simulations were conducted using EPOCH [4].Using: pre-ionised target, circularly polarised gaussian pulse I = 4x1022 Wcm-2, spatial resolution 9 x 15 nm.

Laser produced ion beams are multi-energetic and divergent – energy selection and delivery is required a Gabor Lens is proposed.

A Gabor lens is a space-charge lens that is able to focus ion beams, first proposed in 1947 [5].

Previous work to focus low energy laser-produced ion beams have used quadrupoles or solenoids. The higher energy ions and higher fluxes would require prohibitively high field strengths, as shown in table 1.

1. The divergent ion beam is partially collimated and then focused. 2. The beam passes through an iris, positioned to allow energy selection.3. The beam is collimated by the third lens ready for delivery to the patient. 

[1] Epstein, K. BMJ (2012); 344: e2488[2] http://www.quantumdiaries.org/[3] Murakami M et al. AIP Conf. Proc. 1024, (2008)

Table 2: Parameters of the lens system requirements for proton energies from 70-250MeV, i.e. typical therapy energies [6].

Laser RequirementsELI (Extreme Light Infrastructure) Beamlines Facility in Prague to start experiments in 2015 at intensities ~1023 Wcm-2.Repetition rates of 10Hz or more predicted.

Assuming 109 protons per pulse currents of ~nA can be achieved at 10Hz

Activation and DosimetryActivation of components of the beam delivery system e.g. the irisExisting solutions to the problem from conventional accelerators could be adapted.

Biological effectsThe effects of protons from RF sources are understood - human treatment is established. The effects of high fluxes (full 80Gy dose in a single shot) not understood.

• The effect of high fluxes at low energy (~5MeV) are being investigated

• the effects of high fluxes at 250MeV not yet known.

High fluxes may allow issues with cell repair and the relatively long treatment time to be overcome.

Delivery of total dose with enough precision – patient movement during shot could lead to the wrong part of the patient being irradiated.

• Reduce cost and size: produce high energy ion beams over small distance

• Smaller size means whole system can be mounted in the gantry

• traditional sources cost of the order $100m [1], while laser based solutions are around $10m.

• Versatility - each laser shot can be adjusted to suit the patient

Next generation systems should give the laser parameters required to produce ion beams of a suitable energy, 250 MeV for protons or for 440 MeV/u carbon

Vulcan 10PW should also allow intensities approaching 1023 Wcm-2.

Figure 6: ΔE/E for the Gabor lens at different proton energies [6].

Figure 1: Protons and ions have a beneficial dose deposition profile to tradition radiation sources such as electrons and photons [2].

Using Laser-plasma ions sources

Table 1: Expected field strengths in tesla for a solenoid, quadrupole and Gabor lens for focussing various ion species and energies [6].

Equation 2: The magnetic field required for focussing ions using a Gabor lens or solenoid.

The Gabor lens system for collimation and enegry selectivity

High repetition laser

Target area

Gabor lens 1 Gabor lens 2 Gabor lens 3Iris Beam bend

Cell irradiation area

Ion beam

Figure 5: Schematic of the Gabor lens collimation and energy selection system.

1 2 3Figure 2: Artistic impression of a laser based ion beam treatment system [3].

Equation 1: The Hole-boring velocity – scaling as I/ne.

Figure 4: (a) The HB front at 70.8ωL-1 and (b) proton

energy spectrum from HB acceleration via a 4x1022 Wcm-2 laser pulse.

Hole-Boring Simulations

Figure 3: 3D representation of a laser pulse hole boring into a target.

Figure 7: The rate of cell survival vs. dosedelivered for protons and x-rays. [7].