  Charged particle therapy (CPT) is an advanced modality of radiation therapy
which has grown rapidly worldwide, driven by recent developments in technology
and methods of delivery. To ensure safe and high quality treatments, various
instruments are used for a range of different measurements such as for quality
assurance, monitoring and dosimetry purposes. With the emergence of new and
enhanced delivery techniques, systems with improved capabilities are needed to
exceed existing performance limitations of conventional tools. The Medipix3 is
a hybrid pixel detector able to count individual protons with millisecond time
resolution at clinical flux with near instant readout and count rate linearity.
The system has previously demonstrated use in medical and other applications,
showing wide versatility and potential for particle therapy. In this work we
present measurements of the Medipix3 detector in the 60 MeV ocular proton
therapy beamline at the Clatterbridge Cancer Centre, UK. The beam current and
lateral beam profiles were evaluated at multiple positions in the treatment
line and compared with EBT3 Gafchromic film. The recorded count rate linearity
and temporal analysis of the beam structure was measured with Medipix3 across
the full range of available beam intensities, up to $3.12 \times 10^{10}$
protons/s. We explore the capacity of Medipix3 to provide non-reference
measurements and its applicability as a tool for dosimetry and beam monitoring
for CPT. This is the first known time the performance of the Medipix3 detector
technology has been tested within a clinical, high proton flux environment.
