Abstract Body

Charged particles are to achieve the high dose-rates needed in FLASH radiotherapy, because the photon yield from bremsstrahlung has low efficacy. First results were indeed obtained with electrons, but soon it was shown that cyclotrons used in proton therapy could reach intensities high enough to allow treatments in FLASH regime, at least in 2D. A conformal 3D-FLASH treatment can be performed using 3D-printed range modulators. For heavier ions, synchrotrons are used to accelerate the nuclei to the high energies needed for therapy, and here FLASH dose rate conditions are more difficult to reach than for cyclotrons. We have recently shown that with proper beam adjustment it is possible to get >5·10^{8 12}C-ions in pulses <200 ms, thus enabling FLASH treatments with carbon ions. The use of carbon or heavier ions is interesting for two reasons. First, whether the FLASH sparing effect in normal tissue is also observed at high-LET is very important to understand the physico-chemical mechanisms of the FLASH effect. Second, heavy ion therapy is limited by toxicity in the entrance channel, which may be reduced at ultra-high dose rates. Here we will present the most recent in vitro and in vivo experiments performed at HIT and GSI synchrotrons with ultra-high intensities of ¹²C-ions.