Evaluation of 2D ion chamber arrays for patient specific quality assurance using a static phantom at a 0.35 T MR-Linac.

INTRODUCTION: Patient specific quality assurance (QA) in MR-Linacs can be performed with MR-compatible ion chamber arrays. However, the presence of a static magnetic field can alter the angular response of such arrays substantially. This works investigates the suitability of two ion chamber arrays, an air-filled and a liquid-filled array, for patient specific QA at a 0.35 T MR-Linac using a static phantom. METHODS: In order to study the angular response, the two arrays were placed in a static, solid phantom and irradiated with 9.96 × 9.96 cm2 fields every 10° beam angle at a 0.35 T MR-Linac. Measurements were compared to the TPS calculated dose in terms of gamma passing rate and relative dose to the central chamber. 20 patient specific quality assurance plans were measured using the liquid-filled array. RESULTS: The air-filled array showed asymmetric angular response changes of central chamber dose of up to 18% and down to local 3 mm / 3% gamma rates of 20%, while only minor differences within 3% (excluding parallel irradiation and beams through the couch edges) were found for the liquid-filled ion chamber array without rotating the phantom. Patient plan QA using the liquid-filled array yielded a median local 3 mm / 3% 3D gamma passing rate of 99.8% (range 96.9%-100%). CONCLUSION: A liquid-filled ionization chamber array in combination with a static phantom can be used for efficient patient specific plan QA in a single measurement set-up in a 0.35 T MR-Linac, while the air-filled ion chamber array phantom shows large angular response changes and has its limitations regarding patient specific QA measurements.

Incidence and evolution of venous thrombosis during the first 3 months after irreversible electroporation of malignant hepatic tumours.

The incidence and evolution of venous thrombosis adjacent to the ablation zone after percutaneous irreversible electroporation (IRE) were evaluated to identify potential risk factors in patients with hepatic malignancies. 205 venous structures (in 87 patients) within a ≤1.0 cm radius of the ablation zone were assessed after IRE of 112 hepatic lesions (74 primary, 38 secondary hepatic malignancies) by pre-interventional and post-interventional (1-3 days, 6 weeks and 3 months after IRE) contrast-enhanced magnetic resonance imaging. The relationships between venous thrombosis and clinical features were analysed using a binary logistic regression model. In 27 of 87 patients (31%), a total of 67 venous complications were noted during the 3 months follow-up. Thrombosis represented the most frequently observed complication (n = 47; 70.1%), followed by vessel narrowing (n = 20; 29.9%). 5 (10.6%) of 47 thromboses showed spontaneous regression 3 months after IRE. A small vessel diameter (p = 0.011) and post-interventional vessel narrowing (p = 0.006) were independently associated with delayed post-ablative thrombosis. Delayed venous thrombosis frequently occurs after IRE of hepatic malignancies. Pre-existing vessel narrowing and a small vessel diameter represent significant risk factors that require further surveillance and potentially therapeutic intervention.

Botulinum antibodies in dystonic patients treated with type A botulinum toxin: frequency and significance.

We measured serum antibodies to botulinum toxin (ABT) in 96 patients with focal dystonia who had been treated with type A botulinum toxin. The frequency of detectable ABT was 3% (three patients). Patients with ABT had received more than 50 ng of botulinum toxin, and the shortest time between two injections was significantly less than in patients without ABT. The clinical evolution of the three patients was heterogeneous: one had decreased effectiveness with repeated injections, another had persistent improvement, and the third never responded to toxin injections.

Interaction of Lp(a) with plasminogen binding sites on cells.

Lp(a) competes with plasminogen for binding to cells but it is not known whether this competition is due to the ability of Lp(a) to interact directly with plasminogen receptors. In the present study, we demonstrate that Lp(a) can interact directly with plasminogen binding sites on monocytoid U937 cells and endothelial cells. The interaction of Lp(a) with these sites was time dependent, specific, saturable, divalent ion independent and temperature sensitive, characteristics of plasminogen binding to these sites. The affinity of plasminogen and Lp(a) for these sites also was similar (Kd = 1-3 microM), but Lp(a) bound to fewer sites (approximately 10-fold less). Both gangliosides and cell surface proteins with carboxy-terminal lysyl residues, including enolase, a candidate plasminogen receptor, inhibited Lp(a) binding to U937 cells. Additionally, Lp(a) interacted with low affinity lipoprotein binding sites on these cells which also recognized LDL and HDL. The ability of Lp(a) to interact with sites on cells that recognize plasminogen may contribute to the pathogenetic consequences of high levels of circulating Lp(a).

Clostridium bifermentans serovar malaysia: sporulation, biogenesis of inclusion bodies and larvicidal effect on mosquito.

Sporulation of Clostridium bifermentans serovar malaysia, which has a larvicidal activity towards mosquitoes, was examined by electron microscopy. Parasporal inclusion bodies lacking a crystalline structure were first detected at t5 (5 h after the end of exponentional growth). Also, the presence of "brush-bottle"-like appendages appearing first at t5 was noted; these remained attached to the spores when released after sporangium lysis. Larvicidal activity assayed on Anopheles stephensi larvae appeared at t0 and increased rapidly to a maximum between t5 and t8. However, a decrease in bacterial toxicity occurred with sporangium lysis.

Cloning of a Bacteroides fragilis chromosomal determinant coding for 5-nitroimidazole resistance.

Strain BF8 is a plasmid-free Bacteroides fragilis, resistant to 5-nitroimidazole (5-Ni) antibiotics (metronidazole, ornidazole and tinidazole). The resistance was transferable by conjugation into Bacteroides fragilis BF638R. The total DNA of a Nir transconjugant was used for the construction of a Sau3A genomic library in a B. fragilis cloning vector pFK707 delta H1 (4.2 kb). By electrotransformation of strain BF638R, a recombinant plasmid containing an insert of 5.4 kb was obtained which conferred to the host strain the resistance to 5-Ni. The physical map of the insert was established. After deletion analysis of the insert, the Nir determinant was localized on a HpaII-HincII fragment of 1.6 kb in size. This Nir determinant has been compared by Southern-blot analysis with other Bacteroides Nir determinants of plasmid origin.

Characterization of restriction endonuclease BfrBI from Bacteroides fragilis strains BE3 and AIP 10006.

A new type II restriction endonuclease, named BfrBI, was detected in two strains of Bacteroides fragilis, BE3 and AIP 10006 (NCTC 9343T). The enzyme BfrBI, an isoschizomer of NsiI and AvaIII, recognized the hexanucleotide sequence [5'-ATG decreases CAT-3'], with a cleavage site generating blunt ends.

Use of high-frequency jet ventilation in neonates with hypoxemia refractory to high-frequency oscillatory ventilation.

OBJECTIVE: To describe the response to high-frequency jet ventilation in infants with hypoxemic respiratory failure unresponsive to high-frequency oscillatory ventilation. METHODS: This was a retrospective analysis of chart records on demographics, ventilator settings, blood gas analysis and calculated oxygenation index prior to and during the first 7 days of high-frequency jet ventilation in ten consecutive infants. RESULTS: Before the initiation of high-frequency jet ventilation, the ventilatory mean airway pressure (MAP; cmH2O), fraction of inspired oxygen (FiO2) and oxygenation index on high-frequency oscillatory ventilation were 14.3 +/- 1.3, 0.97 +/- 0.02 and 29 +/- 5, respectively. Three hours after the initiation of high-frequency jet ventilation, the oxygenation index improved to 18 +/- 4 (p < 0.001) and the improvement was sustained during the study period. By 6 h of high-frequency jet ventilation, the FiO2 decreased to 0.62 +/- 0.09 (p < 0.01) and, by 1-3 h of ventilation, the MAP decreased to 10.9 +/- 1.3 (p < 0.01). The improvement in FiO2 persisted for 7 days while, although the MAP remained lower throughout the study, the improvement in MAP failed to reach statistical significance after 72 h. No significant changes in pH, pCO2, or pO2 before or during high-frequency jet ventilation were noted. CONCLUSION: High-frequency jet ventilation improves hypoxemic respiratory failure unresponsive to high-frequency oscillatory ventilation in infants. These findings suggest that not all high-frequency ventilatory devices yield the same clinical results.

[An automatic gas scanning device, technical improvement for obtaining a favourable atmosphere for in vitro culture of anaerobic bacteria]. / Balayage gazeux à l'aide d'un automate, une amélioration technique d'obtention d'une atmosphère propice à la culture en jarre des bactéries anaérobies.

All methods for growth of anaerobic bacteria on solid media depend on the elimination of atmospheric O2 through use of a palladium catalyst (Deoxo-Catalyst), active in presence of at least 5% H2 with resultant formation of water. Anaerobic chambers and jars are the two conventional methods employed. Both are based on the elimination of air by means of a pump and its replacement with gas from a cylinder (evacuation-replacement technique). An alternative chemical technique for use in anaerobic jars consists of adding internal gas-generating sachets. The former techniques are more efficient but the trend, particularly in the clinical laboratories, is to use the simpler chemical system that has two inconveniences: a slow establishment of anaerobiosis, and a high cost. We propose a new system that does not require a vacuum pump and consists in flushing anaerobic jars with a convenient gas mixture (H2, CO2, N2: 4.5; 5; 90.5 v/v) by means of an automaton regulating both time and gas flow. Gas-liquid chromatography analysis of the gas inside the jar shows a rapid elimination of gaseous O2, whose residual concentration is low enough to permit growth of all anaerobes of clinical interest, including those which are more O2-sensitive. Comparative qualitative and quantitative data obtained with all available techniques demonstrate the advantages of the new system.

Genetic basis for antibiotic resistance in anaerobes.

This review focuses on genetic and molecular data regarding antibiotic resistance in anaerobes, particularly Clostridium perfringens, Clostridium difficile, Bacteroides species, and Prevotella species. The determinants of resistance are frequently transferable through a conjugation-like process; plasmid self-transfer, plasmid mobilization, or (in Bacteroides species) chromosomal conjugative elements can be involved. The determinants can be localized on transposons. At the genetic level, resistance determinants can be highly specific for one or several anaerobes or may exhibit homology with genes from aerobes. The latter observation suggests that anaerobes are able to exchange genetic material from a "gene pool" shared with aerobic organisms.

Pasteur, oxygen and the anaerobes revisited.

As a biochemist, Louis Pasteur focused on fermentation, demonstrating that it was a vital process. In 1860, he discovered anaerobic life and the strict anaerobes, particularly those responsible for butyric fermentation. Then, in spite of his lack of medical background, Pasteur turned to investigating the role of bacteria in human and animal diseases. In 1877, Pasteur and Joubert described for the first time a pathogenic anaerobe, the 'septic vibrio' (now Clostridium septicum). Not only was the bacterium cultivated, but the disease symptoms described and the disease experimentally reproduced. Pasteur also described what are now known as mixed anaerobic infections. A historical review of Pasteur's work is made in the light of our present knowledge of this field.