The kinematics of boron compounds in vivo is crucial to fully and safely utilize boron neutron capture therapy. In this paper, we proposed a prompt gamma-ray Compton scatter camera (PG-CSC), which can evaluate the 3-D kinematics of boron compounds without invasion. This PG-CSC combines a Compton camera with prompt gamma-ray analysis. The results of its design optimization and tests using simulations showed that one-hour-measurement was sufficient to evaluate a 3-D boron concentration distribution in a rat's brain with the resolution of 1mm in FWHM.

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We present a preliminary study on the design of a high sensitivity small animal DOI-PET scanner: jPET-RD (for Rodents with DOI detectors), which will contribute to molecular imaging. The 4-layer DOI block detector for the jPET-RD that consists of scintillation crystals (1.4mm x 1.4mm X 4.5mm) and a flat panel position-sensitive photomultiplier tube (52mm X 52mm) was previously proposed. In this paper, we investigate imaging performance of the jPET-RD through numerical simulations. The scanner has a hexagonal geometry with a small diameter and a large axial aperture. Therefore DOI information is expected to improve resolution uniformity in the whole field of view (FOV). We simulate the scanner for various parameters of the number of DOI channels and the crystal length. Simulated data are reconstructed using the maximum likelihood expectation maximization with accurate system modeling. The trade-off results between background noise and spatial resolution show that only shortening the length of crystal does not improve the trade-off at all, and that 4-layer DOI information improves uniformity of spatial resolution in the whole FOV. Excellent performance of the jPET-RD can be expected based on the numerical simulation results.

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A radiophotoluminescent (RPL) glass rod dosimeter (GRD) and a small active volume p-type silicon diode detector are used for the measurement of the helmet output factors from five Gamma-Knife units, which include four Model B units and a Model C unit. The output factors for the five units measured with the GRD from 14,8and 4 mm helmets relative to the 18 mm helmet are 0.984 ± 0.003,0.951 ± 0.003 and 0.884 ± 0.006, respectively. Similarly, the corresponding output factors measured with the p-type silicon diode detector are 0.983 ± 0.002,0.952 ± 0.003 and 0.867 ± 0.015, respectively. The output factors are corrected with the end effect for each helmet of the five units. The end effect time for the four Model B units ranges from 4 sec for the 18 mm helmet to 2 sec for the 4 mm helmet. The results for the Model C unit are within 1 sec for all the helmets. The output factors for the five units obtained from both detectors are in good agreement with the values in a recent publication and the values recommended by Elekta, the device manufacturer, except for that of the 4 mm helmet measured with the GRD. The average GRD output factor for the 4 mm helmet is 1.6% higher than Elekta's value,0.870, but is in good agreement with the published value which was measured using small active volume detectors. The helmet output factors for the five Gamma-Knife units measured with the GRD agree within measurement deviation.

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Plane-parallel ionization chambers that exhibit polar effects with low energy electron beams are recommended for therapeutic electron dosimetry. In this study, the polarity effects of a C-134A ionization chamber, a major commercially available planeparallel ionization chamber in Japan, were characterized as a function of mean energy at various depths. Polarity effects were measured at representative depths along depth dose curves of nominal 4,6,9,12, and 15 MeV electron beams, and were compared with previously reported results. Polarity errors for the ionization chamber studied were shown to monotonically increase with decreasing mean energy at a given depth and were maximal at about 1-2 MeV. It was also shown that polarity errors depended on the energy of the incident electron beam. The polarity error of the C-134A ionization chamber was larger than that of other previously investigated plane-parallel ionization chambers. Because the magnitude of polarity effects should be determined throughout the depth dose curve in therapeutic electron dosimetry, it is always necessary to measure ionizing readings taken at both polarities.

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Vol. 24 (2004) No. 4 p. 131-141

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Vol. 24 (2004) No. 4 p. 154-161

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