## 4 Beam Transport and Delivery Considerations  
Laser production of laser beams has yet to reach the energies and the many other qualities needed for deep seated tumor treatment. Nonetheless proton and carbon ion delivery systems have been considered for laser-driven ion beam radiotherapy (see 1998 work entitled \"Prospect for Compact Medical Laser Accelerators\" [67]). For example, Figure 14 illustrates a comparison between a conventional and optical gantry concept that has been suggested for the laser-driven case [68, 69]. One of the most influential teams involved in developing laser-driven ion beam radiotherapy [70] is in the Radiation Oncology Department at the Fox Chase Cancer Center, in Philadelphia. In a seminal paper in 2003 and updated in 2005 [71, 72] they presented calculations for the design of a spectrometer that allows for adjustable proton energy. A mid-plane aperture could be positioned transversely to \"tune\" proton energy to a desired therapeutic energy window (see Figure 15). The design accommodates the typical broad spectrum and large angular divergence of laser-accelerated protons. Furthermore, suitable upstream collection and collimation optics can improve the overall performance. Figure 13: **(a)** Is conventional TNSA using a bulged target irradiated by a laser. Protons are grey balls and the electrons are the yellow cloud; **(b)** indicates a focused proton beam. Reproduced from [64]. Copyright 2010, AIP Publishing LLC. In a conventional accelerator driven hadron therapy unit the costs involved are so high that to make costs economical a number of different treatment rooms are included as shown in a Section 9 figure. Extensive radiation shielding is required to encapsulate the accelerator, the beam transfer section, the gantry systems and the multiple treatment rooms. The optical gantry concept (Figure 14) suggests that the source (just the laser target in this case), the smaller, lighter gantry system and the patient  
Figure 14: **(a)** Conventional gantry system to direct the ion beam to the patient. This can normally be about 100 tons in weight and very expensive; **(b)** The design of an optical (laser) gantry system which uses mirrors to convey the beam closer to the patient. Reproduced from [68]. Copyright 2002, MAIK “Nauka/Interperiodica”. Figure 15: A particle selector system originally designed by [PERSON] _et al._[70]. This particular diagram of similar design is presented by kind permission of [PERSON] _et al._[25]. In other variants of this system further focusing quadrupoles can be placed at the output [73]. Reproduced from [25]. Copyright 2011, AIP Publishing LLC. could possibly be located in closer proximity. This can potentially reduce radiation shielding requirements and indeed the laser acceleration section requires relatively little. The shielding design for a laser-accelerated proton therapy system has been assessed by [PERSON] _et al._[74]. Monte Carlo simulations determined the shielding necessary for 300 MeV protons and 270 MeV electrons at a laser intensity of 2 \(\times\) 10\({}^{21}\) W\(\cdot\)cm\({}^{-2}\). Neutron production is a key problem and a layer of polyethylene enclosing the whole particle selection and collimation device was used to shield the neutrons. Encapsulating everything a layer of lead was used to reduce the photon dose from neutron capture and electron bremsstrahlung. Simulations showed that a two-layer shielding design with 10-12 cm thick polyethylene and 4 cm thick lead can effectively absorb the unwanted particles to meet the necessary shielding requirements for clinical applications. A report describing all the elements for the development of a laser driven proton accelerator for cancer therapy was published in 2006 [75]. This paper discussed the treatment head of the therapy system, the specifications of the laser system, the particle selection and beam collimation system and an aperture based treatment optimization for laser proton therapy.