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Biomedical subjects

J van Dam

Publications and source records attributed to J van Dam.

14 recordsLinked to original sources
PubMed2006

In vitro evaluation of forces exerted by a new computer-assisted colonoscope (the NeoGuide Endoscopy System).

BACKGROUND: The NeoGuide Endoscopy System (NES) utilizes a fully articulated, computer-controlled insertion tube that allows proximal segments of the colonoscope to follow the path taken by the tip as it is manually advanced through the colon. The system was designed to eliminate looping and scope displacement during colonoscopy. MATERIAL AND METHODS: Using in vitro testing, an inanimate flexible model of the colon incorporating four force transducers located at the key flexure points was employed to measure the axial forces on the colon wall during colonoscopy. In the second part of the study, 10 gastroenterologists performed colonoscopies, using a training latex-based simulator, with the NES and with a standard colonoscope. Colonic displacement was independently assessed by six gastroenterologists, with each evaluating endoscopist assigning a score between 0 and 5 corresponding to the maximum colonic displacement observed at any location. RESULTS: The average measured forces (in lbs) at three of the four flexure points were significantly lower ( P < 0.05) when the NES was used. The mean colonic displacement was significantly lower for procedures performed with the NES compared with the standard colonoscope (2.36 vs. 4.26, P < 0.001). Interobserver agreement regarding the degree of colonic displacement due to looping was moderate (weighted kappa = 0.45, P < 0.01). CONCLUSIONS: Colonoscopy with the NES was associated with significantly less looping and lateral force required for advancement than procedures with a standard colonoscope. The reduced amount of looping suggests that use of the NES in patients might be associated with less discomfort and thus require less sedation.

Biomechanical Phenomena↗
PubMed1995

Quality assurance network in central Europe. External audit on output calibration for photon beams.

The EROPAQ project for TLD monitoring of photon beams started in June 1994 with the set-up of the TLD system: calibration, reading and evaluation procedures. The acceptance level of +/- 3% was set for the TLD intercomparisons. The policy of the project was to check all beams in 47 participating radiotherapy centres and to recheck all the beams in those centres, where a deviation exceeding +/- 3% occurred in one or more of the beams. Out of 129 beams checked, 100 beams (78%) were found within the +/- 3% limit. Eleven beams show deviations larger than +/- 6%, and immediate corrective action was undertaken. Out of 47 centres checked, 22 did not participate in any external audit in a preceding 5 years. In these centres 68% (34/50) of the total number of gamma and x-ray beams checked but only 59% (20/34) of gamma beams were within the acceptance level, while in the 25 centres, which participated in an external audit before, these figures were 84% (66/79) and 88% (35/40) respectively. The sources of discrepancies were thoroughly investigated, discussed with the participants and the errors corrected. Poor results were in several cases associated with very old design of radiotherapy units and old dosimetry systems, equipped with inadequate ionization chambers. In several centres, an insufficient training of the physicists in clinical dosimetry was observed. Thanks to the corrective action, a great improvement of calibration of the beams was achieved. Standard deviation of the distribution of the results for all x and gamma beams checked decreased from SD = 7.4% at the first check to SD = 2.5% at the second check.

Calibration↗
PubMed1994

Reliability of clinical port films for measuring dose inhomogeneities in radiotherapy for head and neck tumours.

Reproducibility and reliability of film dosimetry are evaluated in clinical circumstances. Optical densities were read on 82 routinely taken verification films of Ear-Nose-Throat (ENT) treatment fields and corrected with the sensitometric curve to obtain relative dose values. Off-axis ratios measured on 10 successive films of one specific field were compared with each other and show a good reproducibility (s = 1.7%). Reliability was assessed by comparing 82 off-axis ratios obtained on the films with off-axis ratios obtained by simultaneously performed diode measurements. Only small relative differences were detected (mean = 1.1%, s = 3.0).

Film Dosimetry↗
PubMed1991

In vivo dosimetry for tangential breast irradiation: role of the equipment in the accuracy of dose delivery.

Entrance dose measurements (920) have been performed on both tangential treatment fields for 105 breast cancer patients. About half of them (52) were treated on a modern unit (Mevatron, Siemens), supplied with an automatic verification system, the other half (53) were treated on an old therapy unit (cobalt-60). A team of three radiographers worked on the modern unit, while on the old unit only one radiographer was responsible for the treatment set-up. A small systematic error (+ 1.4%) has been detected on the old unit: a small discrepancy existed in the region of the maximum dose between the measured and the published percentage depth-dose values (Br. J. Radiol., Suppl. 17), the latter being used for dose calculation. A striking difference has been observed for the rate of large deviations (deviations of 5% and more from the mean dose): 2.3% (10/430) for the modern unit versus 15% (75/490) for the old one. This shows clearly that the precision in dose delivery is strongly dependent on the characteristics and staffing of the therapy unit, the modern unit being supplied with a check-and-confirm system and with the beam accessory devices in a fixed position in the beam and a team of radiographers being responsible for the set-up.

Breast Neoplasms↗
PubMed1987

[Households in the reduction stage of the housing market. Analysis of behavior and prospects for the year 2000].

The aging of the Dutch population will lead to a larger demand for housing for the elderly. But this is not the only effect the aging population will have on the housing market. Till the year 2000 the group of households in the reduction stage will grow substantially. These households experience a reduction in size because children leave their parents' home or one of the partners dies. These households behave quite differently on the housing market than younger households. Simulation models have been developed to analyse both growth and composition of the group of older households and their behaviour on the housing market till the year 2000. The result show that the housing needs of the elderly in the future differ widely from those of the present cohorts.

Aged↗