SU-GG-T-75: Phantom Studies of Difficulties with Seed Detection Software Following I-125 Prostate Implants
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Purpose: In our experience, both recent versions (7.1 and 8.0) of the Variseed software have shown variability in seed detection capabilities—wrong identification, missing seeds. A phantom study was begun to improve our understanding of the effectiveness of seed identification in CT scans of patients following prostate implantation. Materials and Methods: A simple planar phantom was constructed for investigation of the effects of seed spacing, orientation, and CT slice thickness on the ability of commercial software to detect the positions and numbers of seeds accurately. Single seed spacings were varied from 4 mm to 11 mm in the longitudinal direction and from 1.9 to 8 mm in the axial plane; stranded seeds (10 mm spacing) were used to test the effect of plane orientations of 90, 75, and 60 deg (relative to the axial CT plane); CT slice thicknesses were varied from 1 to 5 mm; two versions of Varian's seed finder software (7.1 and 8.0) were compared for loose seed detection. V8.0 was used for the angular/slice thickness study. Non-radioactive STM 1251 seeds were supplied by Bard Brachytherapy, Inc. Results: V 7.1 was slightly superior to V8.0 for loose seed identification in the longitudinal (100% vs 93%), but inferior (13% vs 98%) in the cross direction. No effect of slice thickness was observed. Increasing the angle between the seed plane and CT cross plane tended to increase both mean and maximum errors in seed spacing (up to 5 mm). Slice thicknesses of 2 or 3 mm seemed optimal. Conclusions: The seed phantom revealed differences between the two versions of the Variseed software for seed detection, a dependence on seed plane angle and confirmed the recommended CT slice thickness of 2–3 mm (TG137).Carbon-beam therapy has been successfully carried out at HIMAC, Japan. This treatment offers two advantages over conventional radiation therapy: better dose concentration due to the Bragg peak and higher RBE. In treatment planning at HIMAC, the dose distribution is calculated based on dose measurements in water. We previously made three types of phantoms by using CT images: a liver-cancer phantom and two lung-cancer phantoms (one with bone and one without it). This study evaluates carbon-beam attenuation in inhomogeneous layered phantoms and compares their results with beam attenuation in a water phantom. The phantoms consist of plates of tissue-equivalent materials for the x-rays; these plates are stacked along the beam direction. The beam attenuation in the lung-cancer phantom (with bone) is about 23%, similar to the result in the water phantom, attenuation in the lung-cancer phantom (without bone) is about 25%, which is higher than the result in the water phantom by 2%. Finally, the beam attenuation in the liver-cancer phantom is about 33%, which is lower than the result in the water phantom by 3%. Our evaluation of the carbon-beam attenuation using inhomogeneous layered phantoms is successful and comparison with the results in a water phantom is possible.
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Porous SiC Ceramics with Multiple Pore Structure Fabricated via Gelcasting and Solid State Sintering
Porous SiC ceramics with multiple pore structures were fabricated via gelcasting and solid state sintering.A novel gelling agent of Isobam was applied and PMMA was used as both foam stabilizer and pore forming agent.The mechanical properties of porous SiC ceramics were investigated as functions of PMMA content, rotating speed of ball mill, and sintering temperature.With PMMA content increasing from 5wt% to 20wt%, the foaming effect was inhibited while the stability of bubbles increased.When the rotating speed was 220 r/min, the open porosities of the as-prepared SiC ceramics sintered at 2100 varied ℃ from 51.5% to 72.8%, and compressive strength varied from 7.9 to 48.2 MPa.With the rotating speed increasing from 220 to 280 r/min, the foaming effect was aggravated and the porosities of SiC ceramics sintered at 2100 increased.℃ While the sintering temperature increasing from 2050 to 2150 , ℃ the SiC ceramics prepared with PMMA content of 20wt% at rotating speed of 220 r/min decreased in the open porosities while increased in compressive strength.
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ZrB2 based composites containing 10 vol.-% carbon nanotubes (CNTs) are synthesised by spark plasma sintering at temperatures ranging from 1600 to 18008C and at an applied pressure of 25 MPa. The effects of sintering temperature on densification behaviour, microstructural evolutions and mechanical properties are presented. Results indicate that ZrB2-CNT composites fabricated at 16508C have the optimal combination of dense microstructure and properties. The fracture toughness is sensitive to the temperature change and reaches 7.2 MPa m1/2 for the CNT toughened ZrB2 ceramics, which is higher than the measured result for monolithic ZrB2 (3.3 MPa m1/2). The crack deflection and CNT pullout are the dominant toughening mechanisms.
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