RevModPhys.85.751

Al 2006 particle energy selection and beam collimation

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Unformatted text preview: ead ÁE =E ’ 10À2 is required for optimal dose delivery over the tumor region, many have also modeled approaches in which the native broad spectrum of laser-accelerated ions is used to directly obtain the spread out Bragg peak distributions which are normally used to cover the tumor region (Fourkal et al., 2007; Luo et al., 2008) and more in general advanced methods exploiting the properties of laser-accelerated beams (Schell and Wilkens, 2010). An important step in view of their future medical use is to assess the biological effect of laser-driven ions and highlight any peculiarity associated with their pulsed, ultrashort temporal profile. Yogo et al. (2009) first demonstrated the feasibility of cell irradiation studies using laser-driven protons, employing a suitable beam transport setup and then applied a refined technique to infer, via a clonogenic assay, the relative biological effectiveness (RBE) of $2 MeV laser-accelerated protons, as compared to irradiation with a standard x-ray source (Yogo et al., 2011), in human cancer cells. The RBE observed (1:2 Æ 0:1) is comparable with literature results employing rf-accelerated protons of comparable linear energy transfer (LET) (Folkard, 1996). The dose required to 785 cause significant cell damage (typically 1 to several gray) was obtained in several irradiations taking place at 1 Hz repetition rate. Kraft et al. (2010) also carried out proton irradiations of cells, highlighting dose-dependent incidence of a doublestrand DNA break in the cells (see Fig. 36). The peculiar characteristics of laser-driven protons have required the development of innovative dosimetric approaches, as described, for example, by Fiorini et al. (2011) and Richter et al. (2011). In all these experiments, the dose [1–10 grays (Gy)] is delivered to the cells in short bursts of $ns duration. In experiments by Kraft et al. (2010) and Yogo et al. (2011) the dose is fractionated and the average dose rate is comparable to the one used in irradiations with conventional accelerator sources ( $ 0:1 GysÀ1 ). In a recent experiment (Fiorini et al., 2011; Doria et al., 2012) employing a high-energy ps laser system, it was possible to reach up to 5 Gy in a single exposure, reaching dose rates as high as 109 GysÀ1 . This allows access to a virtually unexplored regime of radiobiology, where, in principle, nonlinear collective effects (Fourkal et al., 2011) on the cell due to the high proton density in the bunch may become relevant. Besides cancer therapy, application of laser-driven ion beams in medical diagnosis has also been proposed. MultiMeV proton beams can induce nuclear reactions in low-Z materials (see Sec. V.E) in order to produce neutrons of possible interest for boron neutron capture therapy for cancer, or short-lived positron emitting isotopes which may be employed in positron emission tomography (PET). PET has proven to be extremely useful in medical imaging of blood flow and amino acid transport and in the detecti...
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