166 unifying physics of accelerators, lasers and plasma
plasma acceleration. The state of this rapidly developing area
makes it hardly suitable for textbooks just yet. We will therefore grant only a cursory look at an overview of the presently
identified mechanisms and their scaling rules. We will conclude this chapter with a glimpse into the future.
9.1 Bragg peak
The treatment of tumors with the help of X-rays or proton/ion beams is based on the delivery of energy to malignant
cells of the target volume, intended to prevent and eradicate
the growth of these unwanted cells. We will review the biological effects of radiation in the next section, and will now
compare the effects of the photons with the effects of charged
particles.
FIGURE 9.1
Photon matter interaction, qualitatively.
Photons penetrating through a medium will lose their energy due to several factors. An incident photon can interact
with an atom and get absorbed, causing a photoelectron to be
ejected from the atom. The effect is dominant at lower energies (see Fig. 9.1). An incident photon can also lose part of
its energy via the Compton effect — the inelastic collision of
photons with the electrons of the atoms. Finally, if the energy
of the photon is sufficient, it can create an e + e − pair. This effect has a threshold character and manifests itself for photons
with energies greater than about an MeV.
plasma acceleration. The state of this rapidly developing area
makes it hardly suitable for textbooks just yet. We will therefore grant only a cursory look at an overview of the presently
identified mechanisms and their scaling rules. We will conclude this chapter with a glimpse into the future.
9.1 Bragg peak
The treatment of tumors with the help of X-rays or proton/ion beams is based on the delivery of energy to malignant
cells of the target volume, intended to prevent and eradicate
the growth of these unwanted cells. We will review the biological effects of radiation in the next section, and will now
compare the effects of the photons with the effects of charged
particles.
FIGURE 9.1
Photon matter interaction, qualitatively.
Photons penetrating through a medium will lose their energy due to several factors. An incident photon can interact
with an atom and get absorbed, causing a photoelectron to be
ejected from the atom. The effect is dominant at lower energies (see Fig. 9.1). An incident photon can also lose part of
its energy via the Compton effect — the inelastic collision of
photons with the electrons of the atoms. Finally, if the energy
of the photon is sufficient, it can create an e + e − pair. This effect has a threshold character and manifests itself for photons
with energies greater than about an MeV.