Abstract
tract
The PhD dissertation contributes to study and to advance the application of microdosimetry to
hadron therapy. Hadron therapy could benefit from microdosimetry in different ways. The
treatment plan could be optimised considering microdosimetric quantities, which are more intimately
and directly related to biological effects than the absorbed dose. This also makes microdosimetry
ideal to study and develop dedicated radiobiological models which would provide a more accurate
prediction of biological effects, thus improving treatment efficacy. Further, microdosimetry could
provide a reliable measurement of the radiation quality for quality assurance thanks to its high
sensitivity to radiation quality changes. However, an accredited methodology, standard protocols and
codes of practice are still missing. This work investigated the optimisation of the radiation quality
characterisation of a typical hadron therapy beam. A novel diamond ∆E - E telescope detector was
fully characterised by means of IBIC (Ion Beam Induced Charge) analysis at the Ruder Boskovic
Institute (RBI) in Zagreb (Croatia). The device proved its capability to simultaneously carry out
microdosimetry and particle discrimination, hence its potentiality for the study of secondary
fragments. Further, a number of experimental campaigns were carried out under clinical irradiation
conditions at different facilities, specifically at MedAustron (Austria) employing carbon ions, and at
PARTREC (Netherlands) employing protons. The experiments allowed to study an experimental
methodology to accurately carry out microdosimetry-radiobiology combined measurements, and
to study the optimisation of the radiation quality characterisation employing microdosimeters of
different thickness. The results brought to the conceptualisation and realisation of a novel diamond
microdosimeter: the multi-thickness microdosimeter. Finally, to contribute to the establishment
of a microdosimetric uncertainty budget, a systematic analysis of the contribution of the counting
statistics to the microdosimetric uncertainties was carried out. The study found that rare events
related to nuclear interactions massively degrade microdosimetric uncertainties unless very high
statistics are collected. Guidelines on the statistics required to obtain acceptable uncertainties
were provided. The work motivated the study of the effects of nuclear fragments in microdosimetry.
This was done combining experiments carried out at Trento proton therapy centre (Italy),
and Monte Carlo simulations. A Geant4-based code was developed for the purpose. The work
found a huge impact of secondary fragments on microdosimetric quantities, whose contribution
to the value of ¯yD was higher than 50% in the entrance region of a proton beam. This suggests
nuclear fragments could play an important role in the radiobiological effects as well, hence fosters
an interest in their microdosimetric characterisation and in studying their impact in radiobiology.
In conclusion, the results achieved by this PhD made a step forward in two fundamental directions:
the development and improvement of current detection technology for microdosimetry, and the
establishment of a meticulous experimental method supported by a strong uncertainty analysis.
This work also gave evidence for the importance of studying and taking into account the effects
of nuclear fragments, and proved the suitability of using microdosimetry to address the problem.