On the Role of Single Particle Irradiation and Fast Timing for Efficient Online-Control in Particle Therapy

Within the frame of the CLaRyS collaboration, we discuss the assets of using a reduced-intensity in 19 vivo treatment control phase during one or a few beam spots at the beginning of a particle therapy 20 session. By doing so we can improve considerably the conditions for secondary radiation detection 21 and particle radiography. This also makes Time-of-Flight (ToF) resolutions of 100 ps rms feasible for 22 both the transmitted particles and secondary radiations, by means of a single-projectile counting 23 mode using a beam-tagging monitor with time and position registration. This opens up new 24 perspectives for prompt-gamma timing and Compton imaging for range verification. ToF-based 25 proton computed tomography (CT) and ToF-assisted secondary proton vertex imaging in carbon 26 therapy are also discussed, although for the latter, no evidence of any benefit at small observation 27 angles is anticipated. The reduction of the beam intensity during one or a few spots on the various 28 accelerators for particle therapy should not significantly reduce the patient workflow