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The Czech Boron Neutron Capture Therapy (BNCT) facility works by an epithermal neutron beam installed at the LVR-15 reactor at Rez near Prague. Several configurations of moderating and shielding materials have been designed in order to ensure appropriate parameters of the beam. The beam filter consists of cylindrical layers of Al, AlF3and Ti. To decrease the gamma two layers of Pb are implemented. The filter geometry and composition has been optimized with the aim to increase the epithermal neutron fluence rate and decrease the fast neutron dose rate using the MCNP-4B Monte Carlo code with the DLC-189 library.Suitable patterns of the reactor core were also studied especially in regard to a possible installation of fuel units close to the filter input. Results of calculations show that the optimized variant of the reactor core is able to increase the intensity of the fast neutron source incident to the filter by a factor of 2.0.An experimental verification of the beam parameters was performed using different measurement techniques. The neutron energy spectrum was measured with a set of activation foils, by a Bonner spheres spectrometer and a fast neutron spectrometer with a stilbene crystal. The fast neutron kerma rate was calculated from the spectral measurement. Al-P TLD were used to measure the photon absorbed dose.The beam parameters were measured at 10 MW and were found as follows: the epithermal neutron fluence rate (an energy range from 1 eV to 10 keV) of 9.29 × 10l2m−2s−1, the fast neutron kerma rate in tissue of 2.63 Gy h−1and the incident gamma dose rate in tissue of 2.9 Gy h−1.

Cationic peptides possessing antibacterial activity are virtually ubiquitous in nature, and offer exciting prospects as new therapeutic agents. We had previously demonstrated that such peptides could be produced by fusion protein technology in bacteria and several carrier proteins had been tested as fusion partners including glutathione-S-transferase,S. aureusprotein A, IgG binding protein andP. aeruginosaouter membrane protein OprF. However these fusion partners, while successfully employed in peptide expression, were not optimized for high level production of cationic peptides (Piers, K., Brow, M. L., and Hancock, R. E. W. 1993,Gene137, 7–13). In this paper we took advantage of a small replication protein RepA fromE. coliand used its truncated version to construct fusion partners. The minimal elements required for high level expression of cationic peptide were defined as a DNA sequence encoding a fusion protein comprising, from the N-terminus, a 68 amino acid carrier region, an anionic prepro domain, a single methionine and the peptide of interest. The 68 amino acid carrier region was a block of three polypeptides consisting of a truncated RepA, a synthetic cellulose binding domain and a hexa histidine domain. The improved system showed high level expression and simplified downstream purification. The active peptide could be yielded by CNBr cleavage of the fusion protein. This novel vector was used to express three classes of cationic peptides including the α-helical peptide CEMA, the looped peptide bactenecin and the extended peptide indolicidin. In addition, mutagenesis of the peptide gene to produce peptide variants of CEMA and indolicidin using the improved vector system was shown to be successful.

Salmonella enteritidis 27655-3b and a few diarrheagenic Escherichia coli strains produce morphologically and antigenically related, thin, aggregative fimbriae, collectively named GVVPQ fimbriae (S. K. Collinson, L. Emödy, T. J. Trust, and W. W. Kay, J. Bacteriol. 174:4490-4495, 1992). To determine whether GVVPQ fimbriae are common to Salmonella spp. and other enteropathogenic members of the family Enterobacteriaceae, 113 isolates were phenotypically screened for Congo red binding and aggregative colony morphology. Presumptive positive and representative negative strains were examined by Western blotting (immunoblotting) by using antiserum to SEF 17, the native GVVPQ fimbria of S. enteritidis. Only four S. enteritidis strains and six E. coli isolates possessed substantial amounts of GVVPQ fimbriae after 24 h of incubation on T medium. Following 5 days of incubation, 56 of 93 Salmonella isolates (60%) and 1 of 7 additional E. coli clinical isolates possessed detectable levels of GVVPQ fimbriae. Since variable expression of GVVPQ fimbriae was observed among Salmonella isolates and some E. coli strains produced scant amounts, as revealed by immunoelectron microscopy, the ability to produce these fimbriae was evaluated by genotypic screening. The structural gene for the SEF 17 fimbrin, agfA, was amplified by the polymerase chain reaction, cloned, and sequenced to provide a characterized DNA probe. An agfA DNA fragment hybridized strongly to 603 of 604 (99.8%) Salmonella isolates but very weakly to 31 of 266 other members of the family Enterobacteriaceae including 26 of 137 E. coli strains, 3 of 14 Citrobacter spp., and single isolates of Shigella sonnei and Enterobacter cloacae. The agfA DNA probe proved to be a valuable diagnostic tool for Salmonella isolates arrayed on hydrophobic grid membrane filters. Unique agfA sequences were targeted in the development of a polymerase chain reaction assay specific for Salmonella spp.

Several configurations of moderating and shielding materials have been designed and measured on the LVR-15 reactor for boron neutron capture therapy (BNCT) purposes. To determine the neutron and gamma ray space-energy distributions in the cylindrical geometry the two-dimensional code DOT with the coupled neutron-gamma data library DLC-36 was used. The experimental verification of the beam parameters was performed in the LVR-15 reactor thermal column empty space with layers of graphite, aluminium, alumina, lead and bismuth. Attention was paid to establishing techniques and instrumentation for monitoring the neutron and gamma ray dose and beam quality. The thermal and epithermal (above the Cd resonance) flux densities were measured by activation foils, the neutron spectrum was determined with a Bonner spectrometer and gamma ray background with a scintillation spectrometer. The distribution of thermal neutrons in the human head phantom was mapped with a small semiconductor detector (Si6Li). Thermoluminescence dosemeters (TLD) were used to determine the gamma ray doses in the free beam and in the phantom geometry. The results demonstrate that the maximal thermal flux of 1.02x1013 m-2.s-1 may be obtained at a depth of 3 cm in the polyethylene phantom at reactor power of 1 MW. The therapeutic dose of 20 Gy can be obtained in 31.5 min at the reactor power 5 MW.

The characterisation is described of the epithermal neutron beam at the LVR-15 reactor. The epithermal neutron fluence rate at the reactor power of 10 MW was found to be 1.07 x 1012 m-2.s-1. The fast neutron dose rate was 0.5 Gy.h-1 and the incident gamma dose rate 2.25 Gy.h-1. At this beam whole-body human phantom measurements were designed with the aim of determining both the neutron and gamma dose over the whole body during the irradiation. The thermal neutron fluence rate inside the phantom along its backbone was also measured. A new therapy room for BNCT purposes has been designed to enable irradiation studies without any effect on other users of the LVR-15 reactor. The ground plot of the room has dimensions 3.5 x 2.5 m and the room height is 2 m. The beam filter has been optimised to increase the epithermal fluence rate and decrease the fast neutron dose rate. Influence of the collimator geometry, the Be reflector outside the reactor core, the material and thickness of the filter, and the U converter outside the Be reflector were studied. The calculations were performed with the codes DOT and MCNP. The so far optimal variant shows that it is possible to get an epithermal fluence rate of at least 5.92 x 1012 m-2.s-1 with the fast neutron dose rate of 2.92 Gy.h-1.