Calculation of radiation dose enhancement factors for dose enhancement therapy of brain tumours.

When brain tumours are loaded with iodinated contrast media (CM) and exposed to x-rays, the photoelectrons, Auger electrons and fluorescent x-rays from the iodine enhance the radiation dose absorbed by the tumour. A modified CT scanner, the CTX, can be used to localize the tumour and to deliver the dose enhancement therapy. Monte Carlo calculations are presented here of the central-axis radiation depth dose in a brain containing a tumour loaded with an iodine concentration of 5 mg ml-1 and irradiated with the CTX operated at various kV settings. The dose enhancement factor (DEF) is also calculated for various field sizes and for 5 mg ml-1 of gadolinium in the tumour when the CTX is operated at 140 kV. The calculated values of the DEF are close to published experimental results.     

Penetration of [3H]T-2 mycotoxin through abraded and intact skin and methods to decontaminate [3H]T-2 mycotoxin from abrasions

Penetration of 50 muCi of [3H]T-2 mycotoxin through abraded and intact skin was studied in anesthetized rats sacrificed at 5, 15, 30, 45, 60 and 90 min post-exposure. The greatest penetration was through abraded skin (49 +/- 7%) at 90 min post-exposure, whereas penetration through intact skin (2 +/- 3%) was substantially less (P less than 0.0015). Methods to decontaminate [3H]T-2 mycotoxin from abraded skin over time were studied. Treatment of [3H]T-2 contaminated abrasions by applying Trau + Medic dressing, applying Charcoal Cloth-Anti-bacterial Field Dressing (Charcoal Dressing), or swabbing with povidone-iodine 30 min post-exposure removed 17-32% of the applied [3H]T-2. Immediate blotting with immediate removal of the dressings absorbed 103 +/- 4% (Trau + Medic) and 87 +/- 4% (Charcoal Dressing) of the applied [3H]T-2, while immediate blotting and leaving the dressing in place for 30 min removed 91 +/- 5% (Trau + Medic) and 76 +/- 3% (Charcoal Dressing). It appears that immediate blotting with either dressing followed by immediate removal before application of a clean dressing is an effective method for decontaminating [3H]T-2 from abrasions.     

The changing prevalence of drug-resistant Escherichia coli clonal groups in a community: evidence for community outbreaks of urinary tract infections

A multidrug-resistant clonal group (CgA) of Escherichia coli was shown to cause half of all trimethoprim-sulphamethoxazole (TMP-SMZ)-resistant urinary tract infections (UTIs) in a college community between October 1999 and January 2000. This second study was conducted to determine the fate of CgA. Urine E. coli isolates from women with UTI, collected between October 2000 and January 2001, were tested for antibiotic susceptibility, O serogroup, ERIC2 PCR and DNA macrorestriction patterns using pulsed-field gel electrophoresis. The proportion of UTIs caused by CgA declined by 38% (P<0.001) but the prevalence of resistance to TMP-SMZ did not change. Six additional clonal groups were identified and these were responsible for 32% of TMP-SMZ-resistant UTIs. The temporal decline in the proportion of UTIs caused by CgA provides evidence that CgA caused a community outbreak of UTI. The fluctuation and occurrence of other E. coli clonal groups in this community suggest that a proportion of community-acquired UTIs may be caused by E. coli disseminated from one or more point sources.     

Discriminant analysis.

Discriminant analysis (DA) is a pattern recognition technique that has been widely applied in medical studies. It allows multivariate observations ("patterns" or points in multidimensional space) to be allocated to previously defined groups (diagnostic categories). The relationships between DA and other multivariate statistical techniques of interest in medical studies will be briefly discussed. The main emphasis is on linear discriminant functions (LDF). The theoretic assumptions underlying DA using LDFs will be presented, and the effect of violations to these assumptions will be reviewed in detail. Alternative methods will be presented when violations cause serious problems. It has been shown that the familiar LDF is fairly robust to departures from the assumptions. The application of the LDF in less than ideal situations therefore often does not cause much harm (if the violations are not too grotesque). Another set of problems reviewed is how to estimate the misallocation probabilities when using discriminant functions. The selection of the "best" subset of variables out of the complete set will be discussed. Practical guide lines are given based on the theoretic studies reviewed. When possible, available computer programs for various problems of DA will be indicated. The review does not aim at covering all medical studies where DA has been applied, since emphasis is on the practical conclusions of the theory of DA.     

Renal function of chloralkali workers after the cessation of exposure to mercury vapor

OBJECTIVES: The aims of the study were to assess renal function in chloralkali workers previously exposed to mercury vapor and to assess the impact of selenium status on the biomarkers of kidney function. METHODS: Forty-nine chloralkali workers previously exposed to mercury vapor were compared with 49 age-matched referents in a cross-sectional study. Selected biomarkers of kidney function and biomarkers of selenium status were measured. The index group had been exposed for 13.1 (range 2.8-34.5) years on the average at a mean urinary mercury excretion of 9.3 (range 4.0-25.4) nmol/mmol creatinine a year. The exposure had ceased on an average of 4.8 (range 4.2-10.0) years prior to the examinations. RESULTS: No statistically significant differences were found between the groups for the measured biomarkers of kidney function. The serum selenium concentration and serum glutathione peroxidase activity were associated with the activity of N-acetyl-beta-D-glucosaminidase in urine (U-NAG). The results indicate that having higher glutathione peroxidase activity or a higher serum selenium concentration results in a lower excretion of U-NAG. This effect was the most pronounced in the oldest third of the participants. Apparently the well-known association between U-NAG and age could only be found for the participants with a lower selenium status. CONCLUSIONS: Increased activities of U-NAG during ongoing exposure to mercury vapor appear to be reversible upon cessation of exposure. Selenium status has a substantial impact on U-NAG activity and should be considered in studies of U-NAG excretion.     

Priorities among effective clinical preventive services: methods

Decision makers want to know which healthcare services matter the most, but there are no well-established, practical methods for providing evidence-based answers to such questions. Led by the National Commission on Prevention Priorities, the authors update the methods for determining the relative health impact and economic value of clinical preventive services. Using new studies, new preventive service recommendations, and improved methods, the authors present a new ranking of clinical preventive services in the companion article. The original ranking and methods were published in this journal in 2001. The current methods report focuses on evidence collection for a priority setting exercise, guidance for which is effectively lacking in the literature. The authors describe their own standards for searching, tracking, and abstracting literature for priority setting. The authors also summarize their methods for making valid comparisons across different services. This report should be useful to those who want to understand additional detail about how the ranking was developed or who want to adapt the methods for their own purposes.