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Biomedical subjects

A Nisbet

Publications and source records attributed to A Nisbet.

At least 19 recordsLinked to original sources
PubMed2005

The STRATEGY project: decision tools to aid sustainable restoration and long-term management of contaminated agricultural ecosystems.

The STRATEGY project (Sustainable Restoration and Long-Term Management of Contaminated Rural, Urban and Industrial Ecosystems) aimed to provide a holistic decision framework for the selection of optimal restoration strategies for the long-term sustainable management of contaminated areas in Western Europe. A critical evaluation was carried out of countermeasures and waste disposal options, from which compendia of state-of-the-art restoration methods were compiled. A decision support system capable of optimising spatially varying restoration strategies, that considered the level of averted dose, costs (including those of waste disposal) and environmental side effects was developed. Appropriate methods of estimating indirect costs associated with side effects and of communicating with stakeholders were identified. The importance of stakeholder consultation at a local level and of ensuring that any response is site and scenario specific were emphasised. A value matrix approach was suggested as a method of addressing social and ethical issues within the decision-making process, and was designed to be compatible with both the countermeasure compendia and the decision support system. The applicability and usefulness of STRATEGY outputs for food production systems in the medium to long term is assessed.

Agriculture↗
PubMed2004

The clinical implications of the collapsed cone planning algorithm.

AIMS: The accuracy of computer treatment planning systems is important in achieving clinically acceptable dose distributions. The pencil beam (PB) algorithm on Helax-TMS is currently used for all clinical treatment planning at the two centres involved in this study. However, it has been shown that the Helax-TMS collapsed cone (CC) algorithm is more accurate in regions of heterogeneity, such as the thorax, and head and neck. The aim of this study was to show the actual dose delivered to the patient when treating with a Helax-TMS PB plan, by using the corresponding Helax-TMS CC plan as the reference standard. MATERIALS AND METHODS: Thirty PB treatment plans (for lung and oesophageal treatments) were recalculated using the CC algorithm, and plans were then compared. RESULTS: The number of monitor units required to deliver the prescription dose differed between algorithms, by up to 3.4%. In most cases, the CC algorithm calculated more monitor units than the PB, indicating under-dosage at the prescription point during treatment. The dose distributions also seemed less homogeneous when calculated using the CC algorithm. The minimum dose to the planning target volume (PTV) was lower than the PB plan suggested in every case, by up to 23.2%. ICRU homogeneity requirements (i.e. a minimum 95% of the prescription dose in the PTV) were not met in any of the cases. Even with some attempts at optimisation, conformance to these requirements was difficult. CONCLUSION: The CC algorithm has several factors limiting its suitability for routine clinical use. However, it is an important milestone in radiotherapy treatment planning, and should be used to show expected changes in computer planned dose distributions with new accurate dose algorithms. It is worthwhile considering dose homogeneity requirements well before the advent of anticipated Monte Carlo-based models.

Algorithms↗
PubMed2004

A critical evaluation of the strategy project.

The STRATEGY project (sustainable restoration and long-term management of contaminated rural, urban and industrial ecosystems; www.strategy-ec.org.uk) addressed the need for a holistic decision framework for the selection of optimal remediation strategies for long-term sustainable management of contaminated areas in Western Europe. The project considered both technical and social aspects of implementing restoration strategies for urban and rural environments. The importance of considering socially relevant objectives in addition to the dose reduction was emphasised. A critical evaluation was carried out on 101 selected countermeasures, (including rural waste disposal options), a model was developed to aid optimising countermeasure strategies and a method of carrying out participatory decision-making suggested. The outputs of the project are described and critically evaluated.

Decision Support Systems, Management↗
PubMed2004

Late recurrences of Sydenham's chorea are not associated with anti-basal ganglia antibodies.

Anti-basal ganglia antibodies (ABGA) have been associated with 100% of acute cases and 69% of persistent cases of Sydenham's chorea. We describe two cases of late recurrences of Sydenham's chorea with absence of ABGA. Both patients had several childhood episodes of Sydenham's chorea. MRI imaging of the basal ganglia and exhaustive investigations for other causes of chorea were normal or negative. The absence of ABGA may be evidence against an autoimmune pathology in late and some persistent recurrences. We suggest the likely pathophysiology to be dopamine hypersensitivity of chronically damaged basal ganglia neurones possibly following induction of an autoimmune antibody response in childhood.

Aged↗
PubMed2004

Experiences of a proactive IR(ME)R inspection in radiotherapy.

The Ionizing Radiation (Medical Exposure) Regulations 2000, IR(ME)R, apply to the safety of the patient referred for a medical exposure to ionizing radiation. In Scotland, the Scottish Executive (Department of Health) is responsible for carrying out inspections of compliance with these regulations. IR(ME)R specifically addresses issues concerned with Employer's duties, responsibilities of the Practitioner, Operator and Referrer, justification of individual medical exposures for diagnosis and treatment, optimization of all procedures, clinical audit and adequate training of all duty holders. A proactive IR(ME)R inspection of the Clinical Oncology Department, Raigmore Hospital, Inverness, was carried out in November 2001 by inspectors based at the Department of Health, London, and seconded by the Scottish Executive, Department of Health. The aim of the inspection was to assess the degree of compliance with the regulations. In this case study the experiences of a proactive inspection are described in detail and some of the important elements of implementing IR(ME)R in a department that operates an ISO 9000-2000 Quality Management System addressed. The identification of IR(ME)R Duty Holders' responsibilities is one important aspect which may be inadequately described by the existing Quality Management System documentation. Other key elements of the inspection include the methods of authorizing the justification, the importance of the treatment prescription sheets in the demonstration of compliance with IR(ME)R, patient identification and pregnancy questions and dose recording procedures. The integration of the standard operating procedures as described in Schedule 1 of the regulations is also important. Where the existing Quality Management System documentation is written to include the IR(ME)R requirements of duty holder's responsibilities and the allocation of all the important tasks, then there is no need to re-badge these documents for IR(ME)R purposes. IR(ME)R encourages departments to focus on the safety of the patient and to document good practice. In order to comply, departments will have to show evidence of optimization of their procedures and must address the clinical governance issues associated with delivery of treatment.

Humans↗
PubMed2003

The IPEM code of practice for electron dosimetry for radiotherapy beams of initial energy from 4 to 25 MeV based on an absorbed dose to water calibration.

This report contains the recommendations of the Electron Dosimetry Working Party of the UK Institute of Physics and Engineering in Medicine (IPEM). The recommendations consist of a code of practice for electron dosimetry for radiotherapy beams of initial energy from 4 to 25 MeV. The code is based on the absorbed dose to water calibration service for electron beams provided by the UK standards laboratory, the National Physical Laboratory (NPL). This supplies direct N(D,w) calibration factors, traceable to a calorimetric primary standard, at specified reference depths over a range of electron energies up to approximately 20 MeV. Electron beam quality is specified in terms of R(50,D), the depth in water along the beam central axis at which the dose is 50% of the maximum. The reference depth for any given beam at the NPL for chamber calibration and also for measurements for calibration of clinical beams is 0.6R(50.D) - 0.1 cm in water. Designated chambers are graphite-walled Farmer-type cylindrical chambers and the NACP- and Roos-type parallel-plate chambers. The practical code provides methods to determine the absorbed dose to water under reference conditions and also guidance on methods to transfer this dose to non-reference points and to other irradiation conditions. It also gives procedures and data for extending up to higher energies above the range where direct calibration factors are currently available. The practical procedures are supplemented by comprehensive appendices giving discussion of the background to the formalism and the sources and values of any data required. The electron dosimetry code improves consistency with the similar UK approach to megavoltage photon dosimetry, in use since 1990. It provides reduced uncertainties, approaching 1% standard uncertainty in optimal conditions, and a simpler formalism than previous air kerma calibration based recommendations for electron dosimetry.

Advisory Committees↗
PubMed2001

Radiotherapy equipment--purchase or lease?

Against a background of increasing demand for radiotherapy equipment, this study was undertaken to investigate options for equipment procurement, in particular to compare purchase with lease. The perceived advantages of lease are that equipment can be acquired within budget and cashflow constraints, with relatively low amounts of cash leaving the NHS in the first year, avoiding the necessity of capitalizing the equipment and providing protection against the risk of obsolescence associated with high technology equipment. The perceived disadvantages of leasing are that the Trust does not own the equipment, leasing can be more expensive in revenue terms, the tender process is extended and there may be lease conditions to be met, which may be costly and/or restrictive. There are also a number of technical considerations involved in the leasing of radiotherapy equipment that influence the financial analysis and practical operation of the radiotherapy service. The technical considerations include servicing and planned preventative maintenance, upgrades, spare parts, subsequent purchase of "add ons", modification of equipment, research and development work, commencement of the lease period, return of equipment at the end of the lease period and negotiations at the end of the lease period. A study from Raigmore Hospital, Inverness is described, which involves the procurement of new, state-of-the-art radiotherapy equipment. This provides an overview of the procurement process, including a summary of the advantages and disadvantages of leasing, with the figures from the financial analysis presented and explained. In addition, a detailed description is given of the technical considerations to be taken into account in the financial analysis and negotiation of any lease contract.

Hospital Costs↗
PubMed2000

A collision prevention software tool for complex three-dimensional isocentric set-ups.

During treatment planning it can be difficult to check whether a particular plan is workable, that is it avoids obstructing treatment beams with parts of the patient couch and it avoids collisions between the treatment machine head and the patient couch. To overcome this problem, the trigonometric relationships between the placement of treatment beams and the patient couch are examined. From these relationships a set of useful equations that can be generally applied is derived. The application of these equations practically as a simple (non-graphical) planning tool is described. The resulting tool enables the feasibility of a plan to be checked during treatment planning, and gives guidance as to how a patient could be repositioned to allow the use of a plan when potential beam obstructions are detected, prior to verification of the treatment on a simulator.

Algorithms↗
PubMed1999

An evaluation of epoxy resin phantom materials for megavoltage photon dosimetry.

Epoxy resin phantom materials have been available for some time and are widely used for dosimetry purposes, not least in audit phantoms. Information on their behaviour is partly available in the literature, but there are different mixes and formulations often given similar names and it may not be appropriate to transfer information from one material to another. Five commercially available water substitute materials have been evaluated for use in megavoltage photon beams: WT1, WTe, RMI 451, RMI 457 and 'plastic water'. Four independent experiments were carried out to compare these materials with water in megavoltage photon beams ranging in energy from cobalt 60 to nominal 16 MV x-rays, and some general conclusions are drawn from the results as to their use. All are suitable for relative dosimetry in megavoltage photon beams. However, differences of up to 1% are observed for absolute measurements. The newer formulations, developed for electron beam use, are also closer to water for megavoltage photon beams.

Biophysical Phenomena↗
PubMed1998

A dosimetric intercomparison of kilovoltage X-rays, megavoltage photons and electrons in the Republic of Ireland.

BACKGROUND AND PURPOSE: A comprehensive dosimetry intercomparison has been carried out involving all the radiotherapy centres, all external beam modalities and every radiotherapy treatment unit in the Republic of Ireland. MATERIALS AND METHODS: Reference point measurements were made for all megavoltage photon beams. Doses were also investigated in planned three-field distributions. One of these was in a homogeneous epoxy resin solid water phantom, whilst the second included a lung equivalent insert. The intercomparison was also carried out for three electron energies in each centre. The position of the depth of maximum dose for a standard field size was independently determined, as was the beam energy and a subsequent beam calibration was made. In addition, a kilovoltage X-ray intercomparison was carried out on every kilovoltage quality. RESULTS: For 13 megavoltage photon beams a mean ratio of intercomparison measured dose to locally measured dose of 1.002 was obtained (standard deviation 1.2%). For 12 electron beam measurements a mean ratio of intercomparison measured dose to locally measured dose of 1.018 was obtained (standard deviation 0.8%). For four kilovoltage beams a mean ratio of intercomparison measured dose to locally measured dose of 0.997 was obtained (standard deviation 1.9%). CONCLUSIONS: The intercomparison has given confidence in the basis of clinical delivery of radiation dose in radiotherapy treatment and in the consistency (precision) of dosimetry between different centres within the Republic of Ireland. In addition, it has established a methodology for subsequent ongoing routine radiotherapy dosimetry audit and a baseline set of results to act as an initial reference point.

Humans↗
PubMed1998

Polarity and ion recombination correction factors for ionization chambers employed in electron beam dosimetry.

Polarity and ion recombination correction factors for the NACP (type-02) design parallel-plate ionization chamber employed in a recent UK national electron beam dosimetry intercomparison are derived over the full range of energies and measurement conditions encountered. In addition, these effects have been studied for a further four NACP chambers, a Markus parallel-plate chamber, a Roos parallel-plate chamber and a NE2571 graphite walled cylindrical ionization chamber.

Electrons↗
PubMed1998

Spectral reconstruction of clinical megavoltage photon beams and the implications of spectral determination on the dosimetry of such beams.

An analysis technique, based on simulated annealing, is described which is employed to derive megavoltage photon beam spectral information from narrow beam attenuation measurements. Megavoltage photon beam spectra have been determined using this technique for linear accelerators from different manufacturers, and different models from individual manufacturers at a range of energies from nominal 6 MV to nominal 25 MV. All of the photon beams included in the study are in routine clinical use. The subsequent effects on dosimetry of employing derived primary spectra to specify beam quality are examined. The results suggest that the quality index TPR(20)10 may be insensitive to beam quality changes for high-energy beams in the range of 15 MV to 25 MV. Although the quality index may be insensitive as a beam quality specifier at these higher qualities, the actual difference in the calculated dose delivered using derived spectra as the quality specifier rather than TPR(20)10 is likely to be small, the results obtained indicating a difference of between 0.2% and 0.7% in the calculated dose delivered.

Biophysical Phenomena↗
PubMed1998

An evaluation of epoxy resin phantom materials for electron dosimetry.

The use of epoxy resin 'solid water' (water substitute) phantoms is becoming increasingly common in radiotherapy dosimetry, and depth ionization curves and conversion factors from ionization to dose identical to water have often been assumed. Fluence ratios of water to solid water for WTe (produced by Radiation Physics, St Bartholomew's Hospital, London) and RMI 457 (produced by Radiation Measurements Inc., Middleton, Wisconsin) have therefore been determined and have been found to decrease with energy, which, within measurement uncertainty, can be described with a linear function dependent on mean electron beam energy at the depth of measurement, Ed. The fluence ratios for WTe are very close to unity (i.e. within the measuring uncertainty) for most of the energies examined, the exception being a nominal 20 MeV beam. The results also show that an assumption of unity for the fluence ratios of RMI 457 may introduce a systematic error of the order of 1% in electron beam dosimetry at lower energies. As regards the depth ionization curves measured in the respective solid water materials, these are shown to be in agreement with those measured in water within the limits of the measuring uncertainty.

Biophysical Phenomena↗
PubMed1998

An experimental evaluation of recent electron dosimetry codes of practice.

As from the 1 January 1997, the recent IPEMB code of practice for electron dosimetry is the recommended protocol for electron beam dosimetry in the UK, replacing the previous HPA code of practice and its IPSM addendum. New recommendations for electron beam dosimetry have also been formulated recently by the AAPM and the IAEA on the use of parallel-plate ionization chambers in high-energy electron beams. Against this background, the procedures recommended in each of these codes of practice have been followed from intercomparison of the field instrument ionization chamber with a secondary standard through to the determination of absorbed dose at the reference position in the electron beam. Absorbed doses have been determined for a number of electron beam energies ranging from nominal 5 MeV through to 17 MeV, and for four different types of field instrument ionization chamber: an NE2571 graphite walled cylindrical chamber; an NACP parallel-plate chamber; a Markus parallel-plate chamber; and a Roos parallel-plate chamber. The differences in the determination of absorbed dose between the IPEMB protocol and the HPA/IPSM protocol vary from +0.5% to +1.6% at the depth of maximum dose. In addition the IPEMB measured doses are 0.2% larger than those measured following the IAEA code of practice. It may also be stated that the IPEMB measured doses at the depth of maximum dose are up to 1.5%, but generally less than 1.0%, lower than those measured by the AAPM protocol.

Calibration↗
PubMed1997

A dosimetric intercomparison of electron beams in UK radiotherapy centres.

A dosimetry intercomparison has been carried out for all 52 radiotherapy centres in the UK which possess electron treatment facilities. The intercomparison was carried out on one treatment unit in each centre and for three energies across the range of available energies. The position of the depth of maximum dose for a standard field size was independently determined and a subsequent beam calibration made. The factor to convert the reading on a calibrated ionization chamber to absorbed dose in an electron beam is energy dependent, and hence to carry out an independent calibration measurement also requires the beam energy to be determined. In addition a quantitative measure of the difference in the calibration chains between the intercomparison equipment and the host department's field instrument was carried out. In order to provide a follow-up to the initial IPSM national photon intercomparison, a photon beam calibration was measured in one photon beam in each centre. For 156 electron beam measurements, a mean ratio of intercomparison measured dose to locally measured dose of 0.994 was obtained with a standard deviation of 1.8%. For the 52 photon beam measurements, a mean ratio of intercomparison measured dose to locally measured dose of 1.003 was obtained with a standard deviation of 1.0%.

Electrons↗
PubMed1995

A comparison of two transcutaneous monitors for the measurement of arterial PO2 and PCO2 in neonates.

We examined the ability of two transcutaneous devices (Fastrac, Sensormedics Corporation, Yorba Linda, California, U.S.A. and Hewlett Packard M1018A, Hewlett Packard Component Monitoring System, Hewlett Packard, North Hollywood, U.S.A.) to measure arterial PCO2 and PO2 in neonates. Thirty-seven neonates had transcutaneous oxygen measured with the Hewlett Packard (HPO2 group), 38 neonates had transcutaneous carbon dioxide measured with the Hewlett Packard (HPCO2 group) and the Fastrac was used on 27 neonates (FTCO2 group). Both devices were operated with electrode temperatures of 43.5 degrees C although an additional ten subjects were studied using the Fastrac with an electrode temperature of 43.0 degrees C. The mean differences (transcutaneous--arterial) and upper and lower limits of agreement were calculated for each group. For the HPO2 group they were 3.78 mmHg (-12.23 to 19.80 mmHg), for the HPCO2 group they were 0.40 mmHg (-4.50 to 5.30 mmHg) and for the FTCO2 they were -0.96 mmHg (-7.85 to 5.92 mmHg). For the Fastrac group at an electrode temperature of 43.0 degrees C the mean difference and limits of agreement were -1.00 mmHg and -4.58 mmHg to 2.58 mmHg. The average sensitivity and specificity for both machines for the detection of hypocarbia were 82% and 92% respectively while for hypercarbia they were 90% and 94% respectively. For hypoxaemia, the sensitivity and specificity were 40% and 94% while for hyperoxaemia the sensitivity and specificity were 83% and 97%. We conclude that both machines provide a useful supplement to arterial PCO2 measurements and the Fastrac performs better at 43.0 degrees C. The measurement of PO2 is less accurate but is still of clinical use.

Blood Gas Monitoring, Transcutaneous↗
PubMed1991

The protocols and codes of practice used for the determination of absorbed dose in megavoltage photon and electron beams.

Air kerma-to-dose and exposure-to-dose conversion factors for megavoltage photon beams and electron beams are derived for a variety of commonly used ionization chambers, using the various dosimetry protocols and codes of practice currently in use. It is found that differences in the resultant values are present for both photon and electron beams. For example, for a NE2571 graphite-walled thimble ionization chamber, the maximum variation in the air kerma-to-dose conversion factor for photons, Cw,lambda, occurs at a "nominal" energy of 25 MV, when the difference between the maximum and minimum value of Cw,lambda is 5.4%, whereas the maximum difference between different protocols in the air kerma-to-dose conversion factor for electrons, Cw,e, occurs at Eo = 9 MeV, when the spread between maximum and minimum Cw,e values is 2.7%. An analysis of the conversion factors is undertaken to examine if the numerical or theoretical data are the cause of the discrepancies, and it is found to be a combination of both, although the major contribution to this difference arises from the use of different sets of stopping power ratios in the different protocols.

Calibration↗