No abstract

Recent developments of new therapy techniques using small photon beams, such as stereotactic radiotherapy, require new detectors to precisely determine the delivered dose. The dosimeter has to be as close as possible to tissue equivalence and exhibit a small detection volume compared to the size of the irradiation field, because of the lack of lateral electronic equilibrium in small beam. Characteristics of single crystaldiamond (tissue equivalent material Z = 6, high density) make it an ideal candidate to fulfill most of small beam dosimetry requirements. A commercially Element Six electronic grade synthetic diamond was selected to develop a single crystal diamond dosimeter (SCDDo) with a small detection volume (0.4 mm3). The Monte-Carlo code PENELOPE (parallelized version) was used to optimize both geometry and packaging materials of the diamond detector in order to respect the tissue-equivalent requirement. SCDDo dose profile and output factor (OF) measurements, were performed for small photon beams with a micro multileaf collimator m3 (BrainLab) attached to a Varian Clinac 2100 C linear accelerator. These measurements were compared to different detectors, both active and passive: silicon diode (PTW 60017), EBT2 radiochromic films, PinPoint ionization chamber (PTW 31014). SCDDo presents an excellent spatial resolution for dose profile measurements, due its small detection volume. OFs obtained with SCDDo are very satisfactory from 0.6 × 0.6 cm2 to 10 × 10 cm2 field sizes, compared to PinPoint ionization chamber which underestimates OF values in small beam.

We propose a method for multiresolution image reconstruction in X-ray micro computed tomography (microCT). It can have a variety of applications, from material characterization to small animal imaging studies. The main idea is to recover an overall image of the sample with a coarse resolution, and with a fine resolution for a region-of-interest (ROI). In a zoomin CT type setup, two sets of data are used, taken at different magnifications ratios. They are combined with the help of an analytical relation and the reconstruction is an extension of the filtered back-projection (FBP) algorithm. We present results with simulated data, some performance aspects and a simple noise analysis.

We propose a multiresolution X-ray imaging method designed for non-destructive testing/evaluation (NDT/NDE) applications which can also be used for small animal imaging studies. Two sets of projections taken at different magnifications are combined and a multiresolution image is reconstructed. A geometrical relation is introduced in order to combine properly the two sets of data and the processing using wavelet transforms is described. The accuracy of the reconstruction procedure is verified through a comparison to the standard filtered backprojection (FBP) algorithm on simulated data.