Biomedical subjects

W Mondelaers

Publications and source records attributed to W Mondelaers.

9 recordsLinked to original sources

PubMed2005

Gelina neutron target optimisation.

A study is being performed on the properties of the Geel Electron Linear Accelerator (GELINA), a powerful white neutron source, designed for the high-energy resolution time-of-flight measurements. The main aim of this study is to reduce the time spread of neutrons of the given energy without compromising the neutron yield. Both time spread and neutron intensity influence the experimental accuracy of high-resolution neutron cross section measurements, which are particularly important in the resonance region. The quantities of interest have been simulated with coupled electron-photon-neutron steady state and transient MCNP4C3 calculations. Following benchmarking of the code to the properties of the existing target, neutron yield, energy spectra, resolution functions, and neutron and heat spatial distributions have been determined for various alternative geometries and materials. At a fixed accelerator power, actinides deliver the highest neutron yield and a small target provides the best time resolution. The resulting high-power density requires a joint optimisation of the thermal hydraulics and neutronics properties.

Computer-Aided Design↗

PubMed2001

Characterisation and disintegration properties of irradiated starch.

Irradiation treatment could provide a quick and simple way to modify the physical, chemical and pharmaceutical properties of biopolymers such as starch. Corn, potato and drum dried corn starch were exposed to X-ray and electron beam (e-beam) irradiation treatment at doses of 10, 50 and 100 kGy. The disintegration properties of these starches were compared using alpha-lactose monohydrate tablets containing 5% (w/w) starch as disintegrant. Starch solubility increased, while its swelling capacity decreased with increasing irradiation dose. The irradiation treatment caused fragmentation of the amylopectin fraction. Irradiation modified the different starches thoroughly, showing remarkable differences in disintegration properties after X-ray treatment and e-beam modification. The e-beam modification resulted in significantly higher disintegration times of the tablets.

Molecular Weight↗

PubMed2000

A decomposition study of the EPR spectrum of irradiated sucrose

In general, the EPR spectra of irradiated sugars are very complex because of their multicomponent character. In this study we applied a multivariate statistical method called MLCFA, maximum likelihood common factor analysis, and it predicted at least six components contributing to the total EPR spectrum of irradiated sucrose. Three dominant components have already been isolated in an irradiated sucrose single crystal using electron nuclear double resonance (ENDOR) and ENDOR induced EPR (EI-EPR). Results of EPR simulations based on the ENDOR data are in a reliable agreement with the experimental EPR spectra of irradiated sucrose single crystals.

Journal Article↗

PubMed2000

Theoretical study of the relation between radon and its long-lived progeny in a room.

We present a theoretical study of the complex relation between radon and its long-lived progeny implanted in glass surfaces. The well known (extended) Jacobi room model, which is normally used to describe radon and its progeny in a room, was transformed into a two-parameter model revealing a linear correlation between long term radon exposure and surface activity due to implanted radon decay products. Furthermore, this new approach made integration into a Monte Carlo simulation possible so that the large variation of different room model parameters could be taken into account. This allowed the calculation of a probability distribution for radon exposure from the measurement of the implanted 210Po activity. The availability of a 95% confidence interval for the radon exposure is valuable in the application of retrospective radon assessment in epidemiological studies.

Air Pollution, Indoor↗

PubMed1999

Absorbed dose beam quality correction factors kappaQ for the NE2571 chamber in a 5 MV and a 10 MV photon beam.

Dose to water (Dw) determination in clinical high-energy photon beams with ionization chambers calibrated in terms of absorbed dose to water has been proposed as an alternative to ionization chamber dosimetry based on air kerma calibrations. Dw in the clinical beam is derived using a kappaQ factor that scales the absorbed dose calibration factor in the reference beam to the absorbed dose calibration factor in the user beam. In the present study kappaQ values were determined for the NE2571 chamber in a 5 MV and a 10 MV high-energy photon beam generated at the 15 MeV high-intensity electron linac of the University of Gent. A set of three NE2571 chambers was calibrated relative to the Gent sealed water calorimeter both in 60Co and in the linac beam at a depth of 5 cm and a source to detector distance of 100 cm. Two high-purity chemical water systems were used in the detection vessel of the calorimeter, H2-saturated and Ar-saturated pure water, which are both supposed to give a zero heat defect. TPR20(10) and %dd(10) have been evaluated as beam quality specifiers. Simulations using the BEAM/DOSXYZ Monte Carlo system were performed to evaluate potential corrections on the measured beam qualities. The average kappaQ values measured for the three NE2571 chambers in the 5 MV and 10 MV photon beams are 0.995 +/- 0.005 and 0.979 +/- 0.005 respectively. For the three chambers used, the maximum deviation of individual kappaQ values is 0.2%. The measured beam quality specifiers %dd(10) and TPR20(10) are 67.0 and 0.705 for the 5 MV beam and 75.0 and 0.759 for the 10 MV beam. Although our beam design is very different from those used by other investigators for the measurement of kappaQ values, the agreement with their results is satisfactory showing a slightly better agreement when %dd(10) is used as the beam quality specifier.

Belgium↗

PubMed1999

Grating transition radiation: a source of quasimonochromatic radiation.

We have observed transition radiation at optical wavelengths, emitted by 3-13-MeV electrons interacting with a diffraction grating. Near the direction of specular reflection we observed broadband radiation with the same properties as optical transition radiation from a flat surface. In addition, at large angles with respect to this direction and for low angles of incidence of the electrons on the grating surface, we observed the emission of quasimonochromatic radiation. This grating transition radiation may offer an alternative method for production of quasimonochromatic radiation in the far-infrared to mm wavelength range.

Journal Article↗

PubMed1999

Effect of irradiation, packaging, and postirradiation cooking on the thiamin content of chicken meat.

The effect of irradiation with X rays or electrons, irradiation and storage temperature, and postirradiation cooking on the thiamin content of vacuum- or air-packaged minced chicken meat was examined. Samples irradiated with 3-kGy X rays (50 Gy/min) or electrons (5 kGy/min) contained less thiamin than the control specimens, but no differences between both irradiation methods were detected. The thiamin content in samples stored and/or irradiated at 5 degrees C was between 13 and 24 microg per 100-g product lower than in samples stored and/or ionized at -18 degrees C. The same difference in thiamin content was found for specimens packaged in a vacuum or air package, respectively. Vacuum packaging lead to a greater loss of drip than air-packaged samples. The biggest loss of thiamin, 31.1 and 28.0% for X rays and electron beams, respectively, was measured for vacuum-packaged specimens stored and irradiated at 5 degrees C. Compared with the cooked minced chicken breast meat, a higher thiamin content (6 to 17 microg of thiamin per 100-g product) was obtained for the raw samples. When irradiation and vacuum packaging were compared as two separate preservation techniques, the two methods had approximately the same effect on the thiamin content of the minced chicken meat. The mean temperature of the samples after cooking was 87.2 +/- 4.9 degrees C. However, significant differences in internal temperature after cooking of the samples were measured between air- and vacuum-packaged samples.

Animals↗

PubMed1998

Technetium-99m-MDP scintigraphy and long-term follow-up of treated primary malignant bone tumors.

UNLABELLED: Local malignant bone tumor excision followed by high-dose extracorporeal irradiation (300 Gy) and subsequent reimplantation is a unique technique for treatment of primary bone and cartilage tumors. The long-term scintigraphic findings of irradiated bone autografts in relation to clinical patient data were reviewed retrospectively. METHODS: Thirty-seven patients (12 women, 25 men; age range 13.0-66.7 yr; average age 29.1 yr) were studied. Postsurgical anatomopathological diagnoses included osteosarcoma, 20 patients; chondrosarcoma, 7 patients; and other less-frequent primary osteogenic tumors, 10 patients. Three hundred ninety 99mTc-methylene diphosphonate (MDP) whole-body scans performed between 3 mo and 18.3 yr (mean 6.5 yr) after treatment were reviewed. RESULTS: The 10-yr actuarial survival rate was 78%. After a mean period of 19.4 mo, 6 patients developed a local recurrence, and MDP scintigraphy detected the recurrence in 4. Distant metastases developed in 11 patients (30%), of which 10 were nonosseous. Initially, all autografts appeared as photon-deficient areas. Diffusely increased bone uptake was present at osteotomy sites and at articulating surfaces contiguous with autografts within the first few months after surgery. Of all 25 patients with adequate follow-up, 7 showed persistent decreased uptake up to 129 mo after surgery. The other patients developed partial tracer uptake after 19.6 mo, on average. In 6 patients, scintigraphic images consistent with complete revascularisation were noted later (mean 31.5 mo). Local, sometimes multiple, complications were noted in 22 patients, mainly mechanical graft-related (15) or infections (11). Scintigraphic sensitivity for mechanical complications was 100%. Significantly more fractures and collapses were seen when partial tracer uptake suggestive of revascularisation occurred. Altered bone stress gave rise to focal and diffuse scintigraphic abnormalities, often in the spine and lower extremities. In recent literature, similar clinical complication patterns are found for massive allografts. CONCLUSION: Skeletal scintigraphy is a sensitive technique for evaluating long-term follow-up of massive grafts to treat primary malignant bone tumors. Revascularisation and partial bone ingrowth are not sufficient conditions for a lower complication rate.

Adult↗

PubMed1988

Limb conservation in primary bone tumours by resection, extracorporeal irradiation and re-implantation.

En-bloc resection, extracorporeal irradiation and re-implantation of the irradiated bone have been used to treat 15 patients suffering from primary malignant tumours of bone or cartilage and two with benign lesions. This treatment is an alternative to replacement by prosthesis or allograft bridging techniques. After a mean follow-up of over five years results are encouraging, despite some complications and the relatively long period before weight-bearing is allowed.

Adolescent↗