Measurements of dose distributions in small beams of 6 MV x-rays

Dose distributions produced by small circular beams of 6 MV x-rays have been measured using ionisation chambers of small active volume. Specific quantities measured include tissue maximum ratios (TMR), total scatter correction factors (St), collimator scatter correction factors (Sc) and off-axis ratios (OAR). Field sizes ranged from 12.5 to 30 mm diameter, and were defined by machined auxiliary collimators with the movable jaws set for a 4 cm x 4 cm field size. Due to the lack of complete lateral electronic equilibrium for these small fields, the accuracy of the measurements was also investigated. This was accomplished by studying dose response as a function of detector size. Uncertainties of 2.5% were observed for the central axis dose in the 12.5 mm field when measuring with an ionisation chamber with a diameter of 3.5 mm. The total scatter correction factor exhibits a strong field size dependence for fields below 20 mm diameter, while the collimator scatter correction factor is constant and is defined by the setting of the movable jaws. Off-axis ratio measurements show larger dose gradients at the beam edges than those achieved with conventional collimator systems. Corrected profiles measured with an ionisation chamber are compared with measurements made with photographic film and LiF thermoluminescent dosemeters.     

Monoclonal antibodies reactive with all strains of Haemophilus ducreyi.

We have isolated plasma cell hybridomas which secrete monoclonal antibodies directed against Haemophilus ducreyi. Two of these monoclonal antibodies recognize all strains of H. ducreyi tested to date and are capable of detecting the presence of H. ducreyi in skin lesions produced by this pathogen in experimental animals. These monoclonal antibodies which react with apparently all strains of H. ducreyi have the potential to be developed into a rapid immunodiagnostic test for chancroid.     

Changes in immunoregulatory lymphocyte populations in patients with histoplasmosis

Circulating T-lymphocyte subpopulations were enumerated in 65 patients with histoplasmosis and correlated with the different clinical manifestations of the disease. Acute pulmonary histoplasmosis, rheumatologic, disseminated, and chronic inflammatory manifestations of histoplasmosis were all associated with a significant elevation above normal of OKT₈+ (suppressor-cytotoxic) lymphocytes and a significantly lower than normal OKT₄+ (helper-inducer)-lymphocyte to OKT₈+-lymphocyte ratio. In contrast, cavitary disease was associated with an increase in OKT₄+ lymphocytes, a decrease in OKT₈+ lymphocytes, and a higher than normal OKT₄/OKT₈ ratio. Clinical recovery was associated with normalization of these values. Functional activity determined by coculture techniques correlated closely with T-lymphocyte subset measurements. These distinct subset abnormalities may help monitor immunological aspects of disease activity.     

The lung in cystic fibrosis. A quantitative study including prevalence of pathologic findings among different age groups.

The autopsies of 82 patients with cystic fibrosis were reviewed with respect to pathologic changes in the lungs and their respective prevalence among different age groups. Although bronchitis, mucopurulent plugging, and bronchopneumonia were almost universally present among children of all ages, epithelial metaplasia and bronchiectasis were rarer among infants and progressively more prevalent in older age groups. Emphysema was absent in patients under two years of age and affected 11 per cent of the patients two to six years of age and 40 per cent of the patients older than six years, but was never of a severe degree by the point count method. Pulmonary hemorrhage, although uncommon, was usually associated with prominent arterial vessels in walls of bronchiectatic airways. Quantitative assessment of bronchial glands revealed Reid indices significantly higher in patients with cystic fibrosis when compared to noncystic fibrosis patients, but there was no increase in these indices with the age of the patients. Glandular hypertrophy, predominance of mucous acini within glands, and goblet cell hyperplasia of the bronchial mucosa all suggest an explanation for the copious mucous secretion of patients with cystic fibrosis. However, it was not possible to ascertain whether these findings reflect a general exocrine defect of such patients or whether they were merely a response to chronic airway infection, even though the latter is a more plausible assumption.     

Preparation of a pure autologous biodegradable fibrin matrix for tissue engineering

Parallel to the growing role of tissue engineering, the need for cell embedding materials, which allow cells to stabilise in a three-dimensional distribution, has increased. Although several substances have been tested, fibrin is thus far the only one that permits the clinical application of cultured tissue. To date, can cause severe immunological side effects. The objective of this study was to explore the practicability of obtaining autologous thrombin from a single patient in an adequate concentration and amount. Fibrinogen was cryoprecipitated from 200 ml of freshly-frozen plasma. Thrombin was isolated from the supernatant through ionexchange chromatography. The thrombin was first bound to Sephadex A-50 and then eluated using 2ml of a salt buffer (2.0M NaCl in 0.015M trisodiumcitrate, pH 7.0). The activity of the thrombin (51 NIH ml⁻¹ to 414 NIH ml⁻¹) reached levels comparable to those in commercially available fibrin glues (4–500 NIH ml⁻¹). The study has shown that it is possible to obtain a sufficient amount of autologous thrombin from a single donor to create a fibrin matrix of high efficiency without the risk of immunological and infectious side effects.     

Evaluation of the mixed lymphocyte culture (MLC) assay as a method for selecting unrelated donors for marrow transplantation

Abstract: The utility of the MLC assay as a test of HLA-D region matching and predictor of graft-versus-host disease (GvHD) was evaluated in 435 patients receiving marrow grafts from unrelated donors. Donors and recipients were phenotyped for HLA-A, B and DR antigens by serology, tested in MLC, and retrospectively genotyped for DRB1, B3, B4, B5, DQB1 and DPB1 alleles by PCR/SSOP. Of the 244 HLA-A, B, DR-identical donor-recipient pairs with evaluable MLC and DRB1 typing results available, 208 were matched for HLA-A, B and DRB1, while 36 were matched for HLA-A and B and mismatched for a DRB1 allele. Donor anti-recipient relative responses (RR) in MLC, corresponding to the GvHD vector in marrow transplantation, ranged from 7.2 to 100%, with a median of 4.0%. A comparison of reactivity in MLC between pairs matched versus mismatched for DRB1 alleles showed a significant overlap in the distribution of RRs. Using optimally-defined RR cutoffs of 4 and 16%, no correlation between MLC results and risk of developing clinically significant grades III-IV GvHD (p=0.6 and 0.5, respectively) was found when the contribution of DRB1 mismatch was accounted for. Matching for DRB1 alleles, in contrast, was a better predictor of clinically significant GvHD, with DRB1-matched transplant recipients less likely to develop grades III-IV GvHD than DRB1-mismatched recipients (p=0.14). Among the 208 patients and donors matched for DRB1 alleles, the MLC, although reactive (RR > 4.0%) in 45% of cases, did not predict GvHD. Overall, these results underscore the limitations in using the MLC to predict DRB1 matching or risk of clinically significant GvHD among patients receiving unrelated marrow grafts. The availability of DRB1 allele matching by sequence-specific oligonucleotide probes (SSOP) or by direct sequencing provides a method for donor matching that is rapid, precise and superior to the MLC for predicting clinically relevant outcome.     

Doctors'' characteristics do not predict long-term glycaemic control in type 2 diabetic patients.

Glycaemic control in type 2 diabetic patients varies widely between general practitioners (GPs). To increase our understanding of this variation, linear random effects models were used to examine the predictive value of GP characteristics on the course of annual HbA1c measurements, in 688 newly diagnosed type 2 diabetic patients between one and five years after diabetes diagnosis. We found that characteristics of centrally supported GPs, such as interest in diabetes, experience, practice type, list size, and weekly working hours, did not predict their patients' glycaemic control.