Authors:	Schmitz, Tobias
Title:	ESR-dosimetry in thermal and epithermal neutron fields for application in Boron Neutron Capture Therapy
Online publication date:	29-Mar-2016
Year of first publication:	2016
Language:	english
Abstract:	Dosimetry is essential for every form of radiotherapy. In Boron Neutron Capture Therapy (BNCT) mixed neutron and gamma fields have to be considered. Dose is deposited in different neutron interactions with elements in the penetrated tissue and by gamma particles, which are always part of a neutron field. The therapeutic dose in BNCT is deposited by densely ionising particles, originating from the fragmentation of the isotope boron-10 after capture of a thermal neutron. Despite being investigated for decades, dosimetry in neutron beams or fields for BNCT remains complex, due to the variety in type and energy of the secondary particles. Today usually ionisation chambers combined with metal foils are used. The applied techniques require extensive effort and are time consuming, while the resulting uncertainties remain high. Consequently, the investigation of more effective techniques or alternative dosimeters is an important field of research. In this work the possibilities of ESR-dosimeters in those fields have been investigated. Certain materials, such as alanine, generate stable radicals upon irradiation. Using Electron Spin Resonance (ESR) spectrometry the amount of radicals, which is proportional to absorbed dose, can be quantified. Different ESR detector materials have been irradiated in the thermal neutron field of the research reactor TRIGA research reactor in Mainz, Germany, with five setups, generating different secondary particle spectra. Further irradiations have been conducted in two epithermal neutron beams. The detector response, however, strongly depends on the dose depositing particle type and energy. It is hence necessary to accompany measurements by computational modelling and simulation. In this work the Monte Carlo code FLUKA was used to calculate absorbed doses and dose components. The relative effectiveness (RE), linking absorbed dose and detector response, has been calculated using amorphous track models. For the simulation, detailed models of the irradiation facilities are mandatory. Therefore, also the validation of an enhanced model of the TRIGA Mainz is presented in this work. For all experiments carried out, the measured dose response of the detectors has been evaluated and compared to model predictions. Five materials (alanine, ammonium, calcium, lithium formate, and calcium carbonate) were found suitable for a dosimeter set for the characterisation of thermal and epithermal BNCT neutron fields. Each of these detectors reveals a different behaviour and dose composition. RE-factors have been calculated for each dose component, accounting for its dependence on particle type and energy. Agreement within 5% between model and measurement has been achieved for most irradiated detectors. The irradiation of the ESR detectors can, hence, be a helpful tool in field characterisation and model validation. It could be shown that in some areas ESR detectors are superior to the currently predominant ionisation chambers. How far both types of detectors can be complementary or even synergistic will have to be part of future research.
DDC:	540 Chemie 540 Chemistry and allied sciences
Institution:	Johannes Gutenberg-Universität Mainz
Department:	FB 09 Chemie, Pharmazie u. Geowissensch.
Place:	Mainz
ROR:	https://ror.org/023b0x485
DOI:	http://doi.org/10.25358/openscience-4547
URN:	urn:nbn:de:hebis:77-diss-1000003632
Version:	Original work
Publication type:	Dissertation
License:	In Copyright
Information on rights of use:	https://rightsstatements.org/vocab/InC/1.0/
Extent:	227 S.
Appears in collections:	JGU-Publikationen