1. Context

1.1 The role of radiotherapy in cancer treatment

Radiotherapy is a technique used on 60% of patients with cancer at diagnosis or during the course of the disease. Its aim is to deliver the "right dose in the right place", i.e. to combine local control with minimization of the risk of toxicity to healthy tissues adjacent to the target volume(s).

To achieve this, at least three conditions must be met:

• correct identification of the tumour;

• high-precision radiotherapy planning and treatment (RT-3D, IMRT, etc.);

• and precise treatment.

The corollary of geometric precision (as illustrated by the proton Bragg peak) is...