Dosimetry of the I-Plant Model 3500 iodine-125 brachytherapy source

125I brachytherapy sources have been widely used for interstitial implants for a number of years in several tumor sites, especially the prostate. The design of the new I-Plant Model 3500 iodine source is novel, yet its characteristics are similar to those of two existing designs, Model 6711 and the Symmetra. Dosimetry parameters (including dose rate constant, radial dose function, and anisotropy function, as defined by AAPM Task Group 43) were measured with LiF thermoluminescent dosimeters in water-equivalent plastic phantoms. The dose rate constant was found by direct comparison of calibrated I-Plant Model 3500 and Model 6711 seeds in a solid water phantom, to be 1.01 (cGy/h)/U. The radial dose function and anisotropy function are similar to those of the Model 6711 and Symmetra seeds.     

Fate of genetically modified maize DNA in the oral cavity and rumen of sheep

The polymerase chain reaction (PCR) technique was used to investigate the fate of a transgene in the rumen of sheep fed silage and maize grains from an insect-resistant maize line. A 1914-bp DNA fragment containing the entire coding region of the synthetic cryIA(b) gene was still amplifiable from rumen fluid sampled 5 h after feeding maize grains. The same target sequence, however, could not be amplified from rumen fluid sampled from sheep fed silage prepared from the genetically modified maize line. PCR amplification of a shorter (211-bp), yet still highly specific, target sequence was possible with rumen fluid sampled up to 3 and 24 h after feeding silage and maize grains, respectively. These findings indicate that intact transgenes from silage are unlikely to survive significantly in the rumen since a DNA sequence 211-bp long is very unlikely to transmit genetic information. By contrast, DNA in maize grains persists for a significant time and may, therefore, provide a source of transforming DNA in the rumen. In addition, we have examined the biological activity of plasmid DNA that had previously been exposed to the ovine oral cavity. Plasmid extracted from saliva sampled after incubation for 8 min was still capable of transforming competent Escherichia coli to kanamycin resistance, implying that DNA released from the diet within the mouth may retain sufficient biological activity for the transformation of competent oral bacteria.     

Benefits of treating hypertension in the elderly: should age affect treatment decisions?

Do the benefits of treating hypertension extend equally to all age groups, particularly the very elderly? Several large controlled trials have been published in recent years that confirm the benefits of the treatment of hypertension in terms of morbidity and mortality. However, these trials included only relatively small numbers of patients aged > or = 80 years. Data regarding such patients have been extracted and subjected to meta-analysis, but with inconclusive results. Further difficulties arise as a result of the range of therapeutic agents employed. Therefore, uncertainty still surrounds the value of treating very elderly patients with hypertension. The J-curve hypothesis, i.e. that a blood pressure threshold exists below which there is an increase in the rate of cardiac events, has been a concern in treating elderly patients. Upon close examination, this appears to be spurious. The Hypertension in the Very Elderly Trial study sets out to provide conclusive evidence for the benefits or otherwise of treating hypertension in the very elderly and has just commenced. The results of this trial will not be available for some time. In the meantime, should physicians initiate or continue treatment for very elderly individuals with hypertension? If so, what regimens should be employed and should target blood pressure levels be set? At the present time, it would appear sensible to provide treatment for very elderly patients with hypertension, particularly those with evidence of complications or target organ damage. In relatively healthy individuals with mild-to-moderate hypertension, the guiding principle should be 'the lower the blood pressure the better'. Regarding the choice of therapeutic agent, a low-dose diuretic remains the first choice therapy.     

Group B streptococcal prosthetic joint infections

We report 6 cases of group B streptococcal prosthetic joint infections seen in our institution and review 8 previously reported cases. These 14 patients (6 men and 8 women) had an average age of 69. Seven hip joints and 7 knee joints were affected. Only 4 patients had risk factors for prosthetic joint infection (diabetes mellitus in 2, cancer in 1, and myelodysplasia in 1). The average time from surgery to onset of symptoms was approximately 4 years (range, 5 months to 10 years). Pain in the affected joint was the chief complaint. Six patients had bacteremia. Seven patients had known or suspected foci of infection, which were genitourinary tract (1), skin and soft tissue trauma sites (1), gastrointestinal tract (1), and oropharynx (1). Nine patients required prosthesis removal in addition to antibiotic therapy. Two patients had apparent cure of the infection with retention of the prosthesis. Group B streptococcal prosthetic joint infections appear to be a late complication of prosthetic joint replacement surgery.     

Group C streptococcal infection in a prosthetic joint

We present possibly the first reported case of prosthetic joint infection due to group C Streptococcus in a 53-year-old man. The patient was treated with surgical debridement along with extended intravenous antibiotics and long-term oral penicillin therapy. He was able to retain the prosthesis and at 4-year follow-up had no symptoms or evidence of recurrent clinical infection.