General overview on charged particle therapy: current status and future challenges

Abstract

Ion beam radiotherapy is rapidly growing worldwide: 15 centers are currently operative in Europe (3 for carbon ions also), while other 15 are under construction or in planning stage. The main advantage of charged particles over photons is represented by significantly lower energy deposition in the patient (i.e. similar clinical target coverage combined to reduced dose to the normal tissues). Cyclotrons and synchrotrons are mostly used to accelerate ion beams, while pencil beam scanning modality is replacing passive scattering. Fully rotating isocentric and fixed beam lines can be nowadays be considered as a standard choice for protons and carbon ions, respectively, only two existing facilities (HIT and NIRS) being equipped with a very heavy gantry for carbon ions. Dedicated devices and phantoms for accurate dosimetry, commissioning and fast QA in particle therapy are available, including 2-D scintillators, Bragg Peak and multi-layer ion chambers. In-patient ion range and RBE determination represent the two main specific sources of uncertainty, while organ motion management is still highly challenging. The main research activities include microdosimetry, by means of mini-TEPCs, ultra-thin silicon detectors or synthetic microdiamonds, adaptive radiotherapy using in-room volumetric imaging devices, robust optimization, in vivo range verification (PET, prompt gamma and secondaries, proton radiography). Besides protons and carbon ions, the interest is increasing for fast helium ions, expected as beneficial for paediatric patients, for example, thanks to lower fragmentation tail and RBE than carbon ions, while less lateral beam scattering compared to protons.