PubMed Health⌕ Search

Biomedical subjects

H Weatherburn

Publications and source records attributed to H Weatherburn.

At least 19 recordsLinked to original sources
PubMed2004

A study of scatter in diagnostic X-ray rooms.

An important part of determining the radiation protection requirements during X-ray room design is the calculation of the amount of scatter inside and outside the planned locations of the shielding barriers. In this work, a Monte Carlo code has been developed to calculate the percentage scatter so that the current data can be consolidated and new data can be provided as required. Calculations have been compared with measurements to show that they are representative of scatter found in X-ray rooms. Scatter from the dose-area product meter and the collimator system were found to provide large contributions to the measured scatter. A fluoroscopy room containing a C-arm X-ray set was modelled with the Monte Carlo code. The scatter dose was calculated at an X-ray room entrance behind the protective screen, acting as a secondary barrier, at the radiographer's console. The variation of scatter with the position of the protective screen was studied. An empirical calculation, which provided reasonable agreement with the Monte Carlo calculations, was found by using new data for the variation of scatter from concrete with field size. If a door was placed in the X-ray room entrance behind the protective screen, the results showed that it would not need to be lead lined.

Hospital Design and Construction↗
PubMed2001

Calibration frequency of dose--area product meters.

Calibration of patient dose monitoring devices in diagnostic radiology has become increasingly important in the light of new legislation that requires monitoring of patient dose against local and national diagnostic reference levels. An investigation was conducted into the long-term stability of 41 dose-area product (DAP) meters over a period of approximately 5 years, to assess the suitability of an annual calibration regimen. For DAP meters fitted to overcouch X-ray tubes, 77% of calibrations were within 10%, whilst for undercouch tubes only 50% of calibrations were within 10%. These findings suggest that annual calibration may be too infrequent. Suitable calibration frequencies for different clinical workloads are discussed.

Calibration↗
PubMed2000

Application of regulations to cosmetic lasers in private practice.

Recent years have seen a growth in the number of non-NHS premises, for example beauty salons, offering cosmetic laser treatments such as laser hair removal. By law, such practices are subject to registration and monitoring by Health Authorities. However, a national consensus on appropriate standards is urgently required, particularly on interpretation of the legal requirements for medical direction and operator training, in order to ensure consistency of standards in private practice with lasers across the country. This paper outlines the difficulties experienced in the inspection and registration process, and makes recommendations on appropriate interim standards, pending formal guidance from professional bodies and the promulgation of revised regulations. Until such guidance is in place, it may be wise for Health Authorities to include within their inspection protocols a requirement that applicants for laser registrations produce a statement as to the exact form which medical direction of laser treatment will take, to enable the Health Authority to consider and take advice on its suitability. Similarly a requirement that laser operators are state-registered health professionals will ensure that these potentially hazardous devices are only used by properly qualified operators, whilst professional bodies work towards a consensus on minimum training standards.

Cosmetic Techniques↗
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↗
PubMed1996

External radiation protection audit in National Health Service hospitals. Radiation protecgtion advisors (RPA) of the Nottingham City Hospital NHS Trust and the Oxford Radcliffe Hospital NHS Trust.

Radiation protection advisers are accustomed to carrying out internal audit in organizations for which they provide services but, traditionally, external audit has not been a part of the radiation protection adviser function. To provide an external audit function, two teams of radiation protection advisers undertook external radiation protection audits of their respective organizations, including the radiation protection adviser function itself. These audits were more representative of audits or inspections carried out by government agencies, for example the Health and Safety Executive and the former Inspectorate of Pollution, now the Environment Agency. Subsequently, reports, including recommendations for remedial action, were prepared for each management by the external auditors. The process of setting up and carrying out the external audits is described. Guidelines are suggested for those seeking to carry out an external audit.

England↗
PubMed1994

Re-evaluation of a radiation protection cost benefit analysis study in brachytherapy.

Cost benefit analysis has been in use for many years as a method for making a comparison between the costs of radiation protection and the benefits of reduced radiation exposure. It is advocated by the International Commission on Radiological Protection (ICRP) and the National Radiological Protection Board (NRPB) has given more specific advice relating to the value of the man Sv to be used in the calculation of cost benefit. The purpose of this study is to investigate the changes in the NRPB advice over the last 10 years by correcting all figures for inflation and applying them to a particular radiation protection example. The example employed is a previously published case of the introduction of afterloading brachytherapy equipment at the Christie Hospital, Manchester. It has been shown that for this specific example the NRPB advice at one time led to a large cost benefit, at another time it led to a large cost deficit and later still it again gives a large cost benefit. Application of cost benefit analysis to decision making in radiation protection is therefore shown to be in need of further investigation and clarification before it can be used with confidence.

Brachytherapy↗
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↗
PubMed1984

Interstitial radiotherapy in treatment of superficial tumours of the lower alveolar ridge.

An adaptation of a routine afterloading implant technique for local irradiation of small tumours of the lower alveolar ridge is described. The methods the authors have used for radiation dosimetry are explained and some clinical results in 12 such lesions are presented. The technique has the advantage that the need for mandibular resection may be avoided, although this procedure is still available if the primary treatment fails.

Aged↗
PubMed1984

Conversion factors for calculating mass stopping power ratios.

In order to use an air-filled ionisation chamber for dosimetry of a photon or electron beam in a material, it is necessary to know the restricted (Spencer-Attix) mass stopping power ratio of the material, relative to air. A method is described in which a conversion factor, k, is derived by comparing unrestricted stopping power ratios of various materials (relative to air) with those for water (relative to air). Provided that the material does not differ too greatly in effective atomic number from that of water, this ratio is independent of energy and is a constant for any material both for unrestricted and restricted stopping powers. Values of k have been calculated for 31 materials and application of any one such factor to the restricted mass stopping power ratio of water relative to air allows the appropriate restricted mass stopping power of the material, relative to air, to be derived.

Air↗
PubMed1984

RBE and clinical response in radiotherapy with neutron beams.

Consideration of the clinical results reported, when a cyclotron produced neutron beam was used for treatments in the pelvis region, suggested that a constant RBE of 3 should not have been used for all neutron doses. Instead a variable RBE, which increased from approximately 3 to 8 (with decreasing dose), should have been used. Although some of these RBE values are much higher than 3, they have been observed in clinical practice. An "equivalent photon" isodose plan was produced by employing a variable RBE and, by taking a TDF limit of 86 for bowel, an isoeffect plan was produced. This shows that in the clinical situation under consideration much of the pelvis was overdosed. Doses to tumour cells and late effects are also briefly considered. It is suggested that, in neutron therapy, both an "equivalent photon" isodose plan and an isoeffect plan should be produced prior to treatment.

Dose-Response Relationship, Radiation↗
PubMed1980

Physical measurements with a high-energy proton beam using liquid and solid tissue substitutes.

The measurement of the physical parameters of a high-energy proton beam, using a range of liquid and solid tissue substitutes, is described. The system, the detectors used and the experimental verification of the tissue equivalence of the new tissue substitutes is presented. The measurements with the scattered but uncollimated proton beam in muscle- and brain-equivalent liquids and in water are compared to similar data obtained from the scattered but collimated beam. The effect of lung, fat and bone on the dose distributions in composite phantoms is also investigated and the necessary corrections established. A simulated patient treatment indicated that the Bragg peak can be positioned with an error not exceeding +/- 0.5 mm.

Adipose Tissue↗