  Laser-driven ion beams have gained considerable attention for their potential
use in multidisciplinary research and technology. Pre-clinical studies into
their radiobiological effectiveness have established the prospect of using
laser-driven ion beams for radiotherapy. In particular, research into the
beneficial effects of ultra-high instantaneous dose rates is enabled by the
high ion bunch charge and uniquely short bunch lengths present for laser-driven
ion beams. Such studies require reliable, online dosimetry methods to monitor
the bunch charge for every laser shot to ensure that the prescribed dose is
accurately applied to the biological sample. In this paper we present the first
successful use of an Integrating Current Transformer (ICT) for laser-driven ion
accelerators. This is a non-invasive diagnostic to measure the charge of the
accelerated ion bunch. It enables online dose measurements in radiobiological
experiments and facilitates ion beam tuning, in particular, optimization of the
laser ion source and alignment of the proton transport beamline. We present the
ICT implementation and the correlation with other diagnostics such as
radiochromic films, a Thomson parabola spectrometer and a scintillator.
