Development of a guarded liquid ionization chamber for clinical dosimetry

Liquid ionization chambers are considered superior to air-filled chambers in terms of size, energy dependence and perturbation effects. We constructed and tested a liquid ionization chamber for clinical dosimetry, the GLIC-03, with a sensitive volume of approximately 2 mm3. We also examined two methods to correct for general ion recombination in pulsed photon beams: that of Johansson et al, which modifies Boag's theory for recombination in gases, and an empirical method relating recombination to dose per pulse. The second method can be used even in cases where the first method is not applicable. The response of the GLIC-03 showed a stable, linear and reproducible decrease of 1% over 10 h. The liquid-filled GLIC-03 had a 1.1 +/- 0.4% energy dependence while that of the air-filled GLIC-03 was 2.1 +/- 0.3% between the 6 and 18 MV beams from a Clinac 21EX. The two methods for recombination correction agreed within 0.2% for measurements at 18 MV, 700 V, 100 MU min(-1). Measurements with the GLIC-03 in Solid Water in the build-up region of an 18 MV beam agreed with extrapolation chamber measurements within 1.4%, indicating that the GLIC-03 causes minimal perturbation.

Dynamic Data-Driven Finite Element Models for Laser Treatment of Cancer

Elevating the temperature of cancerous cells is known to increase their susceptibility to subsequent radiation or chemotherapy treatments, and in the case in which a tumor exists as a well-defined region, higher intensity heat sources may be used to ablate the tissue. These facts are the basis for hyperthermia based cancer treatments. Of the many available modalities for delivering the heat source, the application of a laser heat source under the guidance of real-time treatment data has the potential to provide unprecedented control over the outcome of the treatment process [7, 18]. The goals of this work are to provide a precise mathematical framework for the real-time finite element solution of the problems of calibration, optimal heat source control, and goal-oriented error estimation applied to the equations of bioheat transfer and demonstrate that current finite element technology, parallel computer architecture, data transfer infrastructure, and thermal imaging modalities are capable of inducing a precise computer controlled temperature field within the biological domain.

Operational assessment of isoniazid prophylaxis in a community AIDS service organisation in Uganda

SETTING

Isoniazid therapy was shown to be 70% effective at preventing tuberculosis in HIV-infected, PPD-positive Ugandan adults, but the feasibility of implementation outside an efficacy trial has not been established.

OBJECTIVE

To study uptake, adherence and feasibility of a 6-month course of isoniazid preventive therapy in community-based HIV clinics in Uganda.

DESIGN

Observational cohort study describing selection of patients and adherence to isoniazid 300 mg daily. Adherence was measured by clinic attendance, pill counts and urine isoniazid metabolite testing. Implementation was costed on a service delivery basis.

RESULTS

Of 1597 cohort members, 22% were PPD-positive. Over 18 months, 193 PPD-positive individuals were assessed for prophylaxis and 98 (51%) were enrolled. Of those enrolled, 74 (76%) completed their course of isoniazid therapy, and 80% were fully adherent. Symptoms or previous treatment for tuberculosis and suspicion of tuberculous lymphadenopathy were the main reasons for exclusion. The additional cost of providing this service was US $14,549.

CONCLUSION

Clinics specialising in the care of persons with HIV/AIDS can successfully implement isoniazid prophylaxis. Difficulties in excluding active tuberculosis and the costs of running the programme may limit its widespread implementation.

Epithelial barrier function and ultrastructure of gelatinous drop-like corneal dystrophy

PURPOSE

Recently, mutations in the M1S1 gene have been identified as responsible for gelatinous drop-like corneal dystrophy (GDLD). How the abnormal M1S1 gene product causes GDLD is not known, although evidence suggests that it may compromise corneal epithelial function. This investigation attempted to determine the effect of the abnormal M1S1 gene product by assessing epithelial barrier function and epithelial ultrastructure in GDLD corneas.

METHODS

Epithelial barrier function was assessed on the basis of fluorescein uptake. The method used a modified slit-lamp fluorophotometer. High-resolution scanning electron and atomic force microscopy was used to investigate the amyloid deposits and epithelial cell structure.

RESULTS

Epithelial permeability was orders of magnitude higher in GDLD corneas than normal. The structure of the amyloid deposits was characterized, and clear abnormalities in epithelial morphology and cell junctions were observed.

CONCLUSIONS

The high epithelial permeability observed in GDLD corneas was directly correlated with abnormalities in epithelial structure, including irregular cell junctions. This suggests that the abnormal M1S1 gene product may affect epithelial cell junctions resulting in increased cell permeability in GDLD corneas.

Reversal of dysthyroid optic neuropathy following orbital fat decompression

AIMS

To document the successful treatment of five patients with dysthyroid optic neuropathy by orbital fat decompression instead of orbital bone decompression after failed medical therapy.

METHODS

Eight orbits of five patients with dysthyroid optic neuropathy were selected for orbital fat decompression as an alternative to bone removal decompression. Treatment with systemic corticosteroids and/or orbital radiotherapy was either unsuccessful or contraindicated in each case. All patients satisfied clinical indications for orbital bone decompression to reverse the optic neuropathy. High resolution computerised tomographic (CT) scans were performed in all cases and in each case showed signs of enlargement of the orbital fat compartment. As an alternative to bone decompression, orbital fat decompression was performed on all eight orbits.

RESULTS

Orbital fat decompression was performed on five patients (eight orbits) with optic neuropathy. Optic neuropathy was reversed in all cases. There were no cases of postoperative diplopia, enophthalmos, globe ptosis, or anaesthesia. All patients were followed for a minimum of 1 year.

CONCLUSIONS

In a subset of patients with an enlarged orbital fat compartment and in whom extraocular muscle enlargement is not the solitary cause of optic neuropathy, fat decompression is a surgical alternative to bony decompression.

Fine localization of the Nijmegen breakage syndrome gene to 8q21: evidence for a common founder haplotype

Nijmegen breakage syndrome (NBS) is a rare autosomal recessive disorder characterized by microcephaly, a birdlike face, growth retardation, immunodeficiency, lack of secondary sex characteristics in females, and increased incidence of lymphoid cancers. NBS cells display a phenotype similar to that of cells from ataxia-telangiectasia patients, including chromosomal instability, radiation sensitivity, and aberrant cell-cycle-checkpoint control following exposure to ionizing radiation. A recent study reported genetic linkage of NBS to human chromosome 8q21, with strong linkage disequilibrium detected at marker D8S1811 in eastern European NBS families. We collected a geographically diverse group of NBS families and tested them for linkage, using an expanded panel of markers at 8q21. In this article, we report linkage of NBS to 8q21 in 6/7 of these families, with a maximum LOD score of 3.58. Significant linkage disequilibrium was detected for 8/13 markers tested in the 8q21 region, including D8S1811. In order to further localize the gene for NBS, we generated a radiation-hybrid map of markers at 8q21 and constructed haplotypes based on this map. Examination of disease haplotypes segregating in 11 NBS pedigrees revealed recombination events that place the NBS gene between D8S1757 and D8S270. A common founder haplotype was present on 15/18 disease chromosomes from 9/11 NBS families. Inferred (ancestral) recombination events involving this common haplotype suggest that NBS can be localized further, to an interval flanked by markers D8S273 and D8S88.

Low level CO2 effects on pulmonary function in humans

The purpose of the study was to determine whether chamber exposure to low levels of CO2 results in functional alterations in gas mixing and closing volume in humans. Four healthy volunteer subjects were exposed to 0.7% CO2 and to 1.2% CO2. Spirometry, lung volumes, single breath nitrogen washout, diffusing capacity for carbon monoxide (DLCO) by two methods, and cardiac output were measured in triplicate. Values were obtained over two non-consecutive days during the training period (control) and on days 2 or 3, 4, 6, 10, 13, and 23 of exposure to each CO2 level. Measurements were made during the same time of day. There was one day of testing after exposure, while still in the chamber but off carbon dioxide. The order of testing, up until measurements of DLCO and cardiac output, were randomized to avoid presentation effects. The consistent findings were a reduction in diffusing capacity for carbon monoxide and a fall in cardiac output, occurring to a similar degree with both exposures. For the group as a whole, there was no indication of major effects on spirometry, lung volumes, gas mixing or dead space. We conclude that small changes may occur in the function of distal gas exchanging units; however, these effects were not associated with any adverse health effects. The likelihood of pathophysiologic changes in lung function or structure with 0.7 or 1.2% CO2 exposure for this period of time, is therefore, low.