Author Of 2 Presentations
Protons and Carbon Ions
Abstract
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 >5·108 12C-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.ULTRA-HIGH DOSE RATE (FLASH) CARBON ION IRRADIATION: FIRST IN VITRO AND IN VIVO RESULTS
Abstract
Background and Aims
In this work, we present the results of first in vitro and in vivo studies for carbon ion beams irradiation that aim to investigate the biological effects delivered at ultra-high dose rate (FLASH).
Methods
The Heidelberg Ion-Beam Therapy Center (HIT) synchrotron, after technical adaptions, can reliably extract 5×108 12C ions within approximately 150 ms. This yields a dose of 7.5 Gy (homogeneity of ±5%) in a volume of at least 8 mm in diameter and a corresponding dose rate of 40-70 Gy s-1. Additionally, similar beam application but at 8 times higher beam intensity could be recently performed at GSI for carbon FLASH irradiations in mice models (Dose: 12-18 Gy, Dose-rate 60-100 Gy s-1).
Results
For the in vitro experiments a clonogenic survival assay and residual γH2AX foci analysis have been performed. The results of the survival assay demonstrate a significant FLASH sparing effect which is strongly oxygenation-dependent and is mostly pronounced at the concentration of 0.5% O2 but absent at 0% and 21% O2 (fig 1). The γH2AX results shows reduction in the residual foci signal at 1% O2.
The GSI in vivo irradiations of mice models could be successfully performed in the plateau and in the SOBP region (fig 2). The SIS18 synchrotron enables treatment of target volumes of typically 20 cm3 with 15 Gy in 150 ms. Larger volumes seem to be possible.
Conclusions
The in vitro experiments confirm FLASH sparing effect at low oxygen concentrations. The pre-clinical results from the very recent mice model experiments are currently under evaluation.