  Carbon ion radiotherapy is known as a less invasive cancer treatment. The
radiation quality is an important parameter to evaluate the biological effect
and the clinical dose from the measured physical dose. The performance of
SOPHIAS detector, which is the SOI image sensor having a wide dynamic range and
large active area, was tested by using therapeutic carbon ion beam at Gunma
University Heavy Ion Medical Center (GHMC). It was shown that the primary
carbon and secondary particles can be distinguishable by SOPHIAS detector. On
the other hand, a LET dependence was observed especially at the high LET
region. This phenomenon will be studied by using the device simulator together
with Monte Carlo simulation.
