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).
In our report we present the case of a 74-year-old man in whom Pseudomonas aeruginosa was identified unexpectedly in intra-operative samples taken during a one-stage revision total hip arthroplasty (THA). The patient was treated with a post-operative, eight-week antibiotic course and, subsequently, was free of infectious symptoms. However, 6 years later an infection of his THA was detected and Pseudomonas aeruginosa was again isolated. In accordance with traditional thinking this should be classified as a new infection, but some recent findings on the relationship between the host and infecting bacteria allow us to interpret this case as a recurrent infection of THA. It is speculated whether at all, or for how long, it is possible for bacteria to survive on the prosthetic surfaces without either eliciting the host's immune response or severely damaging the surrounding tissues. If it is so, prosthetic joint infection can be understood as a disturbed equilibrium between bacteria colonising the implant and the host's immune mechanisms, and thus this concept could lead to the development of new methods for prevention of this feared THA complication.
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