1. Laser-generated proton beams could provide an alternative approach for hadron therapy by using the hole-boring mechanism to accelerate ions from a laser-produced plasma. 2. A Gabor lens system is proposed to collimate, energy select, and focus the divergent multi-energetic ion beam for delivery to patients. 3. Key challenges include understanding biological effects of high ion fluxes, ensuring precise beam targeting with patient movement, and developing high repetition rate lasers capable of producing clinically relevant ion beam energies.

1. Laser Generated Proton
Beams for Hadron
TherapyChristopher Hughes1, Oliver Ettlinger1, Jonathan Bryanti1, Saleh Alatabi1
1
Imperial 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 Therapy
Hadron 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 Requirements
ELI (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 Dosimetry
Activation of components of the beam delivery system e.g. the iris
Existing solutions to the problem from conventional accelerators could be adapted.
Biological effects
The 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 3
Figure 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. dose
delivered for protons and x-rays. [7].