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Biomedical subjects

P Heeg

Publications and source records attributed to P Heeg.

At least 37 records · Page 2Linked to original sources
PubMed2000

Effective point of measurement of cylindrical ionization chambers for heavy charged particles.

Cylindrical ionization chambers are used for the determination of absorbed dose in beams of heavy charged particles, where the effective point of measurement, Peff (the point in depth to which the measured dose refers), is a priori not known. A measurement of Peff for a Farmer-type chamber in a carbon ion beam is presented. It is based on a comparison of relative depth dose curves measured with a cylindrical chamber and a plane-parallel Markus chamber. Both measurements were compared against another high-precision relative depth dose measurement using large-area plane-parallel chambers. For Peff, a value of 72 +/- 7% of the inner radius of the chamber is obtained. The relative depth dose curve for the cylindrical chamber is calculated using an averaging of the depth dose values over the curved inner surface of the active volume while taking account of the different depths of points on the inner surface. Within the measurement uncertainty of 0.2 mm the measurements agree well with the calculated Bragg curve for the Farmer chamber. The result for Peff is in correspondence with the value suggested in a new code of practice by the IAEA for protons and ions, and somewhat less than that suggested by Palmans for protons. The measurements show that cylindrical chambers are in general well suited for depth dose measurements in fields of heavy charged particles if the correct Peff is used.

Heavy Ions↗
PubMed2000

Microbiological, microstructure, and material science examinations of reprocessed Combitubes after multiple reuse.

UNLABELLED: Reprocessing (repeated cleaning, disinfection, and sterilization) and reuse of single-use medical devices has been performed safely with some devices. The aim of our study was to analyze whether reprocessing of the Combitubes (Kendall-Sheridan, Argyll, NY) airway device, used for emergency endotracheal intubation and difficult airway management, is possible and can be performed appropriately and safely. Microbiological, microstructure, and material science examinations were performed with unused, as well as multiple reused and reprocessed Combitubes. The reprocessing procedure consisted of a cleaning, a disinfection, a final inspection, and a sterilization. Microbiological examinations of multiple reused and reprocessed Combitubes found no test organisms in quantitative cultures. A microbial reduction between four and five log levels compared with nonreprocessed tubes was found. Microstructure analysis for the examination of topographical alterations and changes in the chemical composition of the surface demonstrated nonsignificant alterations between new and reprocessed medical devices. In material science examinations, cuff burst pressures were not different between unused and multiple reprocessed Combitubes. The results of all examinations proved that the decontamination process is adequately effective, and that no significant superficial alterations are generated by the multiple reuse and reprocessing of the Combitubes. To assure uniformly good results, a quality management system must be established and only validated methods should be used. IMPLICATIONS: Reprocessing of single-use medical devices offers the opportunity of significant savings and is already performed with some devices. Microbiological, microstructure, and material science examinations proved that reprocessing of multiple reused Combitubes (Kendall-Sheridan, Argyll, NY), mainly used for emergency airway management, is possible and safe.

Colony Count, Microbial↗
PubMed2000

Quality management of medical physics issues at the German heavy ion therapy project.

For the commissioning and operation of the German Heavy Ion Therapy Project a quality assurance program was developed and successfully applied. The complete radiotherapy process using heavy ions was carefully analyzed and divided into three areas related to beam delivery and control, safety-interlock system and medical physics issues. In this paper, the medical physics issues are addressed. Since the irradiation with heavy ions is a nonstandard modality, new concepts and ion specific tests were developed. As far as possible, national and international standard specifications for radiotherapy were adopted. For each aspect, a performance characteristic and a corresponding acceptance test were introduced. In addition, test characteristics for the constancy tests were established. For all tests, intervention thresholds and test frequencies were specified. Using the described protocol of acceptance tests, the commissioning was passed successfully. The heavy ion irradiation facility was approved by the governmental authorities on the basis of these test results. During clinical operation, constancy tests are performed at the beginning of each treatment period, in order to maintain the quality found during the acceptance tests. Up to now, 48 patients have been treated within 6 treatment periods of 4 weeks each. The concepts used and the tests developed for the quality assurance program may serve as an example of how to introduce systematically a quality assurance program for a new treatment modality.

Brain Neoplasms↗
PubMed2000

Quality assurance for a treatment planning system in scanned ion beam therapy.

Conformal radiation therapy using dynamic beam delivery systems like scanned ion beams requires concise quality assurance procedures for the complete treatment planning process. For the heavy ion therapy facility at GSI, Darmstadt, a quality assurance program for the treatment planning system (TPS) has been developed. It covers the development and updating of software, data protection and safety, and the application of soft- and hardware. The tests also apply to the geometrical precision of imaging devices and the geometrical and dosimetrical verification of dose distributions in different phantoms. The quality assurance program addresses acceptance and constancy tests of the treatment planning program. Results of the acceptance tests served as a basis for its governmental approval. Two main results of the acceptance tests are representative for the overall performance of the system. (1) The geometrical uncertainty that could be achieved for the target point definition, setup accuracy, field contouring, and field alignment is typically 1.5 mm. The uncertainty for the setup verification using digitally reconstructed radiographs (DRR's) is limited to 2 mm. (2) The mean deviations between measured and planned dose values is 3% for standardized cases in a water phantom and up to 6% for more complicated treatment configurations.

Dose-Response Relationship, Radiation↗
PubMed1999

Treatment planning for the heavy-ion facility at GSI.

A new treatment planning program was developed for the heavy-ion therapy facility at GSI. In addition, a concise quality standard for treatment planning has been set up. It covers acceptance and constancy checks of all critical aspects in treatment planning. Dose verification measurements done during the commissioning phase show an overall good agreement with the treatment planning calculations.

Algorithms↗
PubMed1999

Quality assurance at the heavy-ion therapy facility at GSI.

In the present stage between the technological realization and the clinical phase, quality management gains a predominant role at the heavy ion therapy facility at GSI. Specific quality inspection procedures had to be developed for the subsequent parts of the beam delivery system, the treatment planning, the raster scanning device, the patient positioning, the dose verification and the safety interlock system. In the meantime the acceptance test of the whole facility has been carried out and an overview about our first experience with quality assurance procedures at the heavy ion irradiation facility is given, with a special emphasis on the medical physics part.

Calibration↗
PubMed1999

Determination of water absorbed dose in a carbon ion beam using thimble ionization chambers.

The method to measure absorbed dose to water in a field of carbon ions as applied for the heavy ion therapy project at the Heavy Ion Research Laboratory in Darmstadt (GSI), Germany, is described in detail. Thimble ionization chambers with a water absorbed calibration factor are applied. The dose obtained with this method was compared with that obtained at the heavy ion therapy facility HIMAC at the National Institute of Radiological Sciences in Chiba, Japan, using the Japanese code of practice. The agreement found was better than 1%. The combined uncertainty of the determination of absorbed dose to water was estimated to amount to 5%.

Air↗
PubMed1999

[The efficacy of repeated disinfection of disposable gloves during usage].

The efficacy of disinfecting medical gloves with isopropanol 60% (v/v) while they are worn was assessed for 4 different brands of latex gloves (Biogel Diagnistic (A), Safeskin Satin Plus (B), Safeskin LPE (C) and Baxter Non-Sterile Latex Exam Gloves (D)) and one latex-free nitrile glove (100% Nitrile N-Dex (E)). Even in the presence of coagulated blood disinfection of the gloves was more efficient than disinfection of the bare hand. The efficacy of the disinfection of glove C, D and E decreased if 10 disinfections were carried out successively. An increase of perforations detected with the water inflation test according to EN 455-1 was found for brand E. As gloves of brand C and D became tacky after 10 disinfections, they were inappropriate for manual work. As a result, disinfection with isopropanol 60% (v/v) can be recommended for gloves of brand A and B only. Disinfection of these gloves is admissible e.g. after indirect patient contact, taking blood samples or laboratory work if no visible contamination or perforation has occurred. However, after contact with patients suffering from an infectious disease or carrying multiresistant organisms the gloves have to be changed. The same holds true if the gloves might be contaminated with naked viruses (e.g. Poliomyelitis virus), since virucidal alcoholic hand disinfectants require high concentration thus leading to materials incompatibility.

2-Propanol↗
PubMed1998

[Not Available].

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Journal Article↗
PubMed1998

[Not Available].

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Journal Article↗
PubMed1997

[Not Available].

In general, the desinfection of surfaces is done through scrubbing and wiping using substances on the basis of aldehydes, oxidants and tensides. We propose a 4-stage procedure (see Table 1). The concentration of the agent and the duration of application depend on the circumstances, whether one is dealing with a prophylactic measure, a nosocomial infection or an infection which has to be reported. The epidemiologic relevance dictates the extent of desinfection.

English Abstract↗
PubMed1997

[Not Available].

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Journal Article↗
PubMed1997

[A Salmonella epidemic by Salmonella subspecies II 4,12,12,27:b:- at the University Hospital of Tübingen in April 1996].

In April 1996 four patients at the University Hospital of Tübingen became ill with diarrhoea at short intervals; one of the patients also suffered from fever. From stool samples of all four patients Salmonella subspecies II 4,12,27:b:- was isolated; from the patient who had fever the pathogen was also isolated from one blood culture. The patients were treated at different wards of the hospital. All four patients suffered from underlying diseases. In the course of a microbiological examination of the central kitchen staff of the hospital Salmonella subspecies II 4,12,27:b:- was isolated from a stool sample of one of the employees. No contact to cold blooded animals, no travel abroad and no symptoms of gastroenteritis were reported by the employee. When the employee had been temporarily suspended no further Salmonella infections occurred.

Adult↗
PubMed1996

Disinfection of pumice.

Pumice is a potential source of infection for the dental technician and of cross-contamination between different dentures and patients. In this study, the number of microorganisms in two different combinations of pumice and disinfectant was compared with a conventional mixture of pumice and water. The results revealed that under practical conditions the mix of Steribim (pumice containing benzoic acid added by the manufacturer) with water reduced the number of bacteria by 99% compared with a mix of a conventional pumice and water. The addition of an antiseptic product that contained octenidine as active agent to conventional pumice reduced the number of microorganisms by 99.999%.

Anti-Infective Agents, Local↗
PubMed1995

Ethics and the decision making process.

Decision making in a clinical setting is influenced by each individual's ethical and moral principles. This paper considers a case study of a man with Parkinson's disease. The morals and principles held by the participants within the decision making process are defined, described and schematically represented according to their role in the process. The author concludes that this case study has changed her attitude to clinical decision making processes.

Aged↗