ABSTRACT
Hadron therapy, often referred to as ‘particle therapy’, includes the use of protons, carbon ions as well as other less common hadrons such as pions, neutrons, helium, lithium, oxygen and silicon ions to treat tumours. In this chapter, we only describe the use of protons and carbon ions, for which the largest clinical experience, although still modest, has been accumulated. Robert Wilson is considered ‘the father’ of hadron therapy from his seminal description in 1946 that the depth-dose profile of protons in matter had significant increase at the end of their path, the ‘Bragg peak’, and that this might be used to treat deeply located tumours more accurately than with X-rays. The differentiating factor between hadron therapy and electron therapy is this favourable depth-dose distribution which results from the fact that hadrons are much more massive than electrons. While all charged particles have a significant increase in energy deposition per unit distance near the end of their path, electrons are so light that they scatter through tortuous paths and stop at various depths in the patient. Conversely, the more massive hadrons are more difficult to scatter, meaning that they all come to rest together at approximately the same depth, a phenomenon which we observe as the familiar Bragg peak. The technical challenge is therefore to be able to accelerate these hadrons to the very high energies required to reach the necessary depth in human patients.
