Carbon Nanotube and Carbon Fibre Based Radiation Dosimetry

Abstract

The principle of radiobiology and, hence, clinical outcomes in radiotherapy are inherently dependent on accurate radiation dosimetry. Over the last few decades, ionization chambers, thermoluminescence dosimeters (TLDs), film dosimeters, and semiconducting dosimeters have been commonly used in radiotherapy. However, the shortcomings of each type of dosimeter limit their applications for in vivo radiation measurements for provision of accurate and precise dosimetric information in real-time. The objective of this thesis is to explore a new generation of radiation dosimeters by using state-of-the-art nanomaterials and technologies to realize real-time monitoring of dose delivery in radiotherapy. This thesis investigates the use of carbon nanotubes (CNTs) and carbon fibres as sensing materials for dosimetric measurements. First, a parallel plate ionization chamber with CNT electrodes was designed to study the ionization collection efficiency of the CNTs. The prototype chamber had two stainless steel electrodes, which were customized to accommodate the CNT samples. Experiments, such as saturation characteristics, linearity, and electrode separation, were performed to characterize the prototype chamber. Secondly, dosimeters based on the resistance change of CNTs and carbon fibres were studied. The proposed dosimeters, based on carbon fibre sheets and CNT films, were designed and fabricated. Dose rate, dose, and field size measurements were carried out to evaluate these novel dosimeters that were able to provide dose rate and dose information at the same time. Thirdly, a transparent and flexible CNT-based film dosimeter was investigated. The flexible dosimeter can perform dosimetric measurements when it was bent to fit the curvature of the measured surface. Finally, a dosimeter array system, consisting of a CNT-based film dosimeter array, a readout circuit, and user interface software, was designed and implemented. The array with the parallel electrode structure and a 3 × 3 mm^2 sensing area for each pixel provided good signal responses. The array system displayed excellent repeatability in the measurements.