Radiation Dosimeter Using an Extrinsic Fiber Optic Sensor

A novel extrinsic optical fiber X-ray dosimeter for biomedical applications is presented in this paper. The primary focus of the sensor is to measure low doses of ionizing X-ray radiation. The material in the sensor tip scintillates upon exposure to radiation and the resultant low level scintillating light is coupled to a polymethylmethacrylate plastic optical fiber, which guides it toward a distant fluorescent optical spectrometer. The optical spectrometer measures the low level scintillating light from the sensor and converts the ionizing radiation energy to measurable arbitrary optical intensity units. Initial testing showed the scintillating optical fiber X-ray dosimeter exhibits an acceptable sensitivity upon excitation from a calibrated X-ray source. Further examinations of the sensor revealed good response and repeatability of measurement for various levels of low energy ionizing X-ray energy. The sensor was found to exhibit a maximum of 3.23% variance from the average value over ten repetitions. The sensor is sensitive from 50 kVp X-ray energy which continued exponentially up to 140 kVp where the response began to taper off. The sensor demonstrated excellent spectral response upon exposure to 6 MV and 15 MV ionizing X-ray radiation energy from a Siemens Avant Garde linear accelerator. It showed excellent repeatability of measurement upon repeated actuation of the radiation over short bursts of time. The sensor demonstrates very good stability of response during on radiation periods, showing a maximum of 2% variation of the full scale value in each case. This type of optical fiber X-ray dosimeter was tested in the University of Limerick (Ireland), the National Institute for Lasers, Plasma and Radiation Physics (Romania), and the Galway Clinic in Ireland. Further investigations were performed by all three facilities to better characterize additional features of the sensor for different X-ray radiation energies.