Influence of Ionization Quenching in Plastic Scintillator Particle Dosimetry
Abstract
Radiotherapy has been used for more than a century to treat cancer and an important part of the treatment with radiation is to direct a sufficiently high dose to the tumour without damaging the neighbouring tissue. The recently commissioned Danish Centre for Particle Therapy (DCPT) features a scanning proton beam that enables the delivery of a more conformal dose to the tumour than what can be achieved with conventional radiotherapy. The present work investigates the use of plastic scintillation detectors (PSDs) coupled to optical fibres as a radiation detector in ion beams. PSDs are attractive for particle dosimetry and particularly in vivo measurements due to a prompt response, small size, and near water-equivalence. It is demonstrated how a single PSD can detect the spots in a scanning beam and measure the scattering of the spots. The conversion from the PSD luminescence response into an energy deposition is, however, challenging. The PSDs exhibit a non-linear response—termed ionization quenching—to charged particles. A theoretical formalism is developed in order to predict and correct the quenched luminescence of PSDs irradiated with ions at clinically relevant energies. The algorithm is based on fundamental scintillator properties and track structure theory and validated relative to a gas-filled detector and Monte Carlo simulations. The combination of a theoretical quenching model, experiments, and Monte Carlo calculations provides a new insight into the quenching of plastic scintillators. Finally, a graphite calorimeter was constructed and subsequently tested in the proton beam at DCPT. The portable calorimeter showed an excellent stability and reproducibility and enables the measurement of more accurate quenching corrections for PSDs.
Info
Thesis PhD, 2019
UN SDG Classification
DK Main Research Area
Science/Technology
