Distributed polymer optical fibre sensors for advancing radiotherapy

This thesis presents the use of polymer optical fibre for enhancing the measurement of radiation dose in radiotherapy. The methods of sensing with this fibre depend on the direct alteration of the inherent characteristics of the fibre. The alterations used are radiation-induced attenuation (RIA) and radiation-induced refractive index change (RIRIC). This thesis aims to investigate how polymer optical fibre (POF) reacts to low doses of radiation from X-ray and proton, and how this can be utilized to measure the dose in real-time during radiotherapy. The response to neutrons was also investigated as they are contaminants that exist at high energy radiation. The fibre was evaluated with various radiation sources at different facilities, including TRIUMF in Vancouver, Canada, Hospital Universitario Central de Asturias (HUCA) in Spain and Galway Clinic in Galway, Ireland. The results revealed that perfluorinated polymer optical fibre was a suitable material for developing a system that can measure the dose at a specific point on a fibre, as it had high sensitivity and repeatability over a wide range of wavelengths. It is more sensitive than undoped polymethyl-methacrylate (PMMA) fibre. The sensitivity of PMMA fibre was enhanced by adding Trans-4-Stilbene Methanol (TS) as a dopant. Fibre Bragg gratings (FBGs) were embedded in different types of polymer fibre, such as benzyl-dimethylketal (BDK) doped PMMA, diphenyl disulfide (DPDS) doped PMMA and cyclic transparent amorphous fluoropolymer (CYTOP® ) and tested with X-ray and proton. They showed a Bragg wavelength shift (BWS) that was proportional to the dose received. The FBGs in BDK doped PMMA show a better consistency in their BWS as compared to other POFs. The FBGs demonstrated a good potential for measuring the dose at discrete points along the fibre and are therefore applicable for quasi-distributed dosimetry application. This study contributes to the advancement of photonics in the development of optical dosimeters in radiotherapy.