In the real-time tumor-tracking radiotherapy (RTRT) system, the fiducial markers are inserted in or near the
target tumor in order monitor the respiratory-induced motion of tumors. During radiation treatment, the markers
are detected by continuous fluoroscopy operated at 30 frames/sec. The marker position is determined by means
of a template pattern matching technique which is based on the normalized cross correlation. With high tube
voltage, large current and long exposure, the fiducial marker will be recognized accurately, however, the radiation
dose due to X-ray fluoroscopy increases. On the other hand, by decreasing the fluoroscopy parameter settings,
the fiducial marker could be lost because the effect of statistical noise is increased. In the respiratory-gated
radiotherapy, the error of the image guidance will induce the reduction of the irradiation efficiency and accuracy.
In order to track the marker stably and accurately in low dose fluoroscopy, we propose the application of a
recursive filter. The effectiveness of the image processing is investigated by tracking the static marker and the
dynamic marker. The results suggest that the stability and the accuracy of the marker tracking can be improved
by applying the recursive image filter in low dose imaging.
We propose the application of nitroanisole as a two-dimensional detector for infrared (IR) phase-shifting interferometry. The nitroanisole that is utilized in our experiment is liquid at room temperature and it has significant thermal lens effect, i.e. the refractive index for visible light is dependent on temperature. In addition, we verified by infrared absorption spectroscopy that the nitroanisole has an absorption band around 10.6μm in the IR region. Therefore, the interference fringe pattern that is generated on the nitroanisole by the IR beams may be treated as a phase grating for visible light. A Fresnel diffraction pattern made by visible laser light that is transmitted through the phase grating, i.e. the nitroanisole, can be observed as a superposition of the intensities corresponding to the profile of the phase grating and its harmonic components. Additionally, in response to a shift of the interference fringe on the nitroanisole, the Fresnel diffraction pattern on the observation plane also shifts by an equal amount. Utilizing this characteristic of nitroanisole, we attempted to estimate the IR phase map by applying the phase-shifting method to the diffraction patterns. We conducted an experiment aimed to measure the angle of a wedge of ZnSe, which is an IR transmitting material, and we confirmed the feasibility of obtaining phase measurements in the IR region by this procedure.