Microdosimetry for hadron therapy: towards optimised beam quality characterisation
Creators: name: Parisi, Gabriele
Publisher: name: University of Surrey
Year: 2024
Subjects: Microdosimetry
Hadron therapy
Protons
Carbon ions
Secondary fragments

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