  With the continued evolution of modern radiation therapy towards high
precision delivery of high therapeutic doses to the tumour while optimally
sparing surrounding healthy tissue, imaging becomes a crucial component to
identify the intended target, properly position it at the treatment site and,
in more advanced research applications, visualize the treatment delivery. This
contribution reviews the main role of imaging in modern external beam radiation
therapy, with special emphasis on emerging ion beam therapy techniques, which
aim at exploiting the favourable properties of ion interaction in matter for
unprecedented ballistic accuracy in dose delivery
