Institute Of Physical Sciences Research Articles

Evaluation of dose calculation algorithms using different density materials for in-field and out-of-field conditions

The accuracy of the dose calculation is vital in the stereotactic ablative body radiotherapy (SABR) technique to achieve clinically effective dose distribution for better tumor control. Multiple commercial radiotherapy treatment planning systems (TPS) were implemented with different algorithms, such as Acuros XB in Eclipse and Superposition in XiO. The aim of this study is to investigate five different dose calculation algorithms, namely, pencil beam convolution (PBC), Acuros XB, AAA implemented in an Eclipse system, collapsed cone convolution (CCC) algorithm implemented in Mobius3D and superposition algorithms implemented in the XiO system, and then validate the results against measurements using an Institute of Physical Sciences in Medicine (IPSM) phantom with different density materials for in-field and out-of- field conditions. The IPSM phantom was used to investigate the dose calculation algorithm performances in four different densities (water, lung, ribs, and dense bone) using different beam configurations, including small beam fields utilised in lung SABR. Five commercial algorithms implemented in two TPS (Eclipse and XiO) and one plan check(M3D) system were used for in-field and out-of-field measurement. In the in-field condition, the Acuros XB algorithm had lower mean differences than the measured dose by the IC ranging from -0.46 to 0.24for all the densities. In the out-of-field condition, the results of eclipse system: AAA, PBC and Acuros XB algorithms demonstrated underdose point's measurements by -40% for all densities except for AAA calculations in lung density (overdosed by 40%). The measured points of the superposition algorithms were overestimated to the actual dose less than 30% in water, lung and dense bone. At the same densities, the CCC algorithms showed relatively the lowest differences in percentage compared to the superposition algorithms. Our results showed that the Acuros XB and superposition algorithms are closer to the actual measured dose than AAA, PBC and CCC for majority of the field conditions for water-equivalent, lung, rib and dense bone densities. The CCC algorithm resulted in a better agreement with the measurement of the out-of-field points compared with the other algorithms.

Evaluation of Mean Glandular Dose during Diagnostic Mammography Examination for Detection of Breast Pathology, in Ethiopia

Background: A mammography examination facilitates the early detection of breast cancer. However, the potential risk of radiation-induced carcinogenesis is also increased with such a procedure. Thus assessment of the breast dose is important. Objectives: The objectives of this study were to investigate the techniques currently used for diagnostic mammography in Ethiopia, thereby to estimate the mean glandular dose (MGD) for Ethiopian women. Materials and methods: A cross-sectional study was conducted on breast cancer patients between 40-64 years of age having compressed breast thickness (CBT) greater than 2 cm. Five mammographic units and 386 women having a total of 1463 mammograms were included in the study period from April 2011-February 2012 in Addis Ababa, Ethiopia.The characteristics of the radiographic equipment and the exposure data of each patient were recorded using designed format. The MGD was calculated from the measured Entrance Surface Air Kerma (ESAK) using appropriate conversion coefficients. The obtained data were analyzed using statistical software. Results: The range of CBT was 2.2-7.5 cm for CC mammograms with mean ± SD of 4.24 ± 1.1 cm and 2.3-8.0 cm in MLO projection with mean ± SD of 4.64 ± 1.1 cm. The average MGD per exposure was 2.57 ± 2.1 mGy while the respective averages separately for the CC and MLO projections were 2.58 ± 2.2 mGy and 2.57 ± 2.1 mGy, respectively. Conclusion: The average MGD values recorded in this study were between the limiting value of the Institute of Physical Sciences in Medicine (2.0 mGy) and American College of Radiology (3.0 mGy) recommendation. These ensure that the mammography examination performed in Ethiopia was capable of achieving acceptable dose levels for patient safety.

Options for radiation protection of the patient

In 2001 the Institute of Physical Sciences in Medicine published a report [1] on cost-effective methods of dose reduction in medicine. Options were compared by assigning a monetary value to radiation risk enabling a comparison to be made between a given radiation detriment and the cost of implementing a measure that would reduce it. While Moores [2] has argued that large dose saving costs (£600 million per annum) may be justifiable irrespective of the actual doses received, Williams [3] has suggested that risks resulting from some lower dose procedures might be regarded as negligible. More recently, Clarke [4] has indicated that existing international recommendations on dose reduction may be too closely linked to formal cost–benefit analysis. Clarke [4] has summarized the current intentions of the International Commission on Radiological Protection (ICRP) with regard to occupational and public exposure. Optimization of individual exposure, particularly that of the most exposed group of persons, is preferred over measures to limit collective dose. While patient exposure is not specifically targeted, the approach may nonetheless be relevant in any such review. At a meeting at the British Institute of Radiology (BIR) in 2004 [5] aspects of dose reduction in diagnostic radiology were considered. Areas identified with potential for further optimization were

Assessment of mean glandular dose in mammography.

The routine assessment of patient dose in the National Health Service Breast Screening Programme is performed as part of the quality assurance protocol recommended by the Institute of Physical Sciences in Medicine. The mean glandular dose to a standard breast is deduced from measurement of the air kerma at the entrance surface of a 4 cm Perspex phantom by applying a series of conversion factors. The exposure factors for this measurement are those used clinically. The measured mean glandular dose is then compared with nationally accepted action levels. In some centres the assessment of mean glandular dose using Perspex is supplemented by patient dose surveys. The mean glandular dose to a series of patients attending a breast screening unit may be estimated from a knowledge of the exposure factors and compressed breast thickness, using a knowledge of the X-ray tube output. Measurements made on units in the Northern Region of England and in Scotland using both methods are presented. The implication of these measurements with regard to patient dose surveys in mammography and quality assurance programmes are discussed. An analysis of the uncertainties associated with the measurement techniques is presented.

Quality assurance in dental radiology by the diagnostic radiology topic group of the institute of physical sciences in medicine

Quality assurance in dental radiology by the diagnostic radiology topic group of the institute of physical sciences in medicine

External Beam Treatment Planning: Can we deliver what we plan?

Many sources of uncertainty exist in the delivery of the prescribed dose to the specified target volume in external beam radiotherapy. Their magnitudes are compared with recommendations for the overall accuracy of dose delivery (+/- 5%). Five dose intercomparisons are reviewed, including a recent UK survey undertaken by the Institute of Physical Sciences in Medicine (IPSM). For phantom doses, standard deviations in the ratio of stated to delivered doses range from 1-3.5%, with larger uncertainties when irradiation of volumes within anthropomorphic phantoms is considered. In addition, uncertainties arise from geometrical discrepancies, and the role of portal films in their assessment is also considered. Imaging during radiotherapy will be increasingly important in the development of complex conformal treatments, where the shape of the target volume may be irregular.

Book reviews

This book is a compilation of papers that were presented at a meeting entitled “Computers in Diagnostic Radiology” organized by the Institute of Physical Sciences in Medicine, which was held at Newcastle upon Tyne during 1989. The book consists of 24 chapters from authors who originate mainly from UK centres.

The significance of patient weight when comparing X-ray room performance against guideline levels of dose

It is gratifying to have so quick and detailed a response as given by Williams and Catling in their comments on our letter (Hart & Shrimpton, 1991). We agree that it is essential for patient dose measurements to be conducted efficiently whilst also yielding meaningful data. Indeed, the need for such local surveys has lead to the formulation of appropriate dosimetry protocols by NRPB in collaboration with the Institute of Physical Sciences in Medicine and the College of Radiographers which will be published shortly.

Memorandum from the Institute of Physical Sciences in Medicine

At present, the dosimetry of low- and mediu-energy X-radiation for radiotherapy purposes in the UK is based on the method recommended in International Commission on Radiation Units and Measurements (ICRU) Report 23 (1973), and incorporated into the current Hospital Physicists' Association (HPA) code of practice (1983). The essential points are summarized here using the same symbols and units as in the code of practice. For an X-ray beam between 150 kV and 300 kV (0.5 mm Cu and 4 mm Cu half-value layer (HVL)), ICRU recommended that output measurements should be made using an ionization chamber with its centre 5 cm deep in a water phantom. Absorbed dose is given by: or by: where D = absorbed dose to water in grays at the position of the centre of the chamber, with the chamber replaced by water, R = instrument reading, corrected to the same standard ambient conditions as the calibration factor, N k = calibration factor to convert the instrument reading to air kerma in grays for standard ambient conditions (at present 20°C, 1013 mbar, and 50% RH for calibrations at NPL), N x = calibration factor to convert the instrument reading to exposure in röntgens for standard ambient conditions, F = a conversion factor, in rad/röntgen, which depends on the HVL of the X-ray beam being used.

Measuring the filtration of mammographic X-ray tubes with molybdenum targets

The method employed in this work, to estimate the filtration of mammographic X-ray sets, makes use of the measurement of the half-value layer (HVL) of the X-ray beam, which is filtered by the air path, the X-ray tube window, an added molybdenum filter and a known thickness of Perspex. Sets of data have been calculated that relate the measured HVL to the added molybdenum filter thickness. The mammographic X-ray sets included in this study were all Siemens Mammomat 2 type, which have molybdenum targets and molybdenum filters and the compression plates employed have a Perspex equivalence of about 1 mm or 2 mm. The kilovoltage is produced by a high-frequency generator and has a nominally constant potential waveform. It is often necessary to determine the HVL of mammographic X-ray sets, for two different reasons: (a) measurement of mean glandular breast dose (Institute of Physical Sciences in Medicine (IPSM), 1989), and (b) determination of total filtration by the HVL method. The estimation of total filtration of X-ray tubes with tungsten targets has previously been given some attention by the author (Cranley & Fogarty, 1988). In addition, errors in the HVL method have been analysed (Gilmore & Cranley, 1990). The IPSM method of estimating breast dose has become widely adopted by physicists involved in the NHS Breast Screening Programme. The method involves the determination of both incident air kerma (for correct exposure of a phantom representing the standard breast) and HVL of the incident X-ray beam. The compression device should be in position for these measurements, to satisfy the standard breast conditions. It is necessary, therefore, to have the compression device in position during the measurement of the HVL. The requirement to estimate the filtration of the mammographic X-ray beam comes from the International Commission on Radiation Protection (ICRP) (1982), which recommends that the total permanent filtration should be equivalent to at least 0.5 mm aluminium or 0.03 mm molybdenum. This implies that the total filtration should be estimated with removable filters, such as the compression plate, excluded. The current method allows the HVL to be measured

BIR Bulletin

The code, published by the Institute of Physical Sciences in Medicine (IPSM, 1990) recommends that the type NE 2561 therapy-level ionization chamber, manufactured by NE Technology Ltd, should continue as the secondary standard chamber when calibrated by the National Physical Laboratory (NPL) in terms of absorbed dose to water. The NPL absorbed dose calibration service offers calibrations for cobalt-60 γ radiation and seven X-ray qualities between 4 and 19 MV with beam filtrations matching those of clinical beams where possible. Absorbed dose to water is given by the product of the corrected electrometer reading with the secondary standard in water and the NPL calibration factor for the incident radiation quality. The NPL beam quality is expressed in terms of quality index, i.e. tissue phantom ratio of 20 to 10 cm depths in water with a constant field size of 10×10 cm.

Quality assurance of ultrasound test objects

A recent survey on ultrasound tissue equivalent test objects carried out by the Institute of Physical Sciences in Medicine clearly shows these objects to have limited useful lifetimes with deterioration setting in within 1 year of purchase.

British science journals are being revamped

This year the Royal Society of London's scientific journals are undergoing their first major reorganization in many years, the intention being to interest a broader international audience and to attract a wider range of prospective authors. The changes include new procedures for submitting papers to the physical and mathematical sciences journal Proceedings of the Royal Society of London, Series A . Previously, a researcher had to contact a fellow or foreign member of the Royal Society and persuade him or her to communicate the paper to a journal. Clearly, for authors residing outside the U.K., that was not always an easy or convenient thing to do, says Michael E. Fisher, a professor in the Institute for Physical Science & Technology at the University of Maryland, College Park, and a regional editor of Proceedings A . Furthermore, the fellow in question might well not be very expert in the subject of the author's paper, which can certainly be ...

An alignment test jig for measuring the effective focal-spot size of mammographic X-ray tubes

Following publication of the Forrest Report (Department of Health and Social Security (DHSS), 1986) and with the implementation of a breast cancer screening programme in the UK, there is considerable interest in the technical aspects of mammographic systems. The equipment requirements for mammographic X-ray screening units have been identified (DHSS, 1987) and guidance on the commissioning and routine testing of mammographic X-ray equipment is also expected (Institute of Physical Sciences in Medicine (IPSM), 1989). These documents relate to all aspects of the mammographic X-ray set including the specification and measurement of the size of the X-ray tube focal spot. It is recommended (DHSS, 1987) that effective focalspot sizes are measured using a pair of slit radiograms in the manner described in BS 6530 (British Standards Institution (BSI), 1985). This standard provides details on the construction of the slit diaphragm and the geometry to be employed when performing focal-spot measurements. In particular, the method requires that the centre of the slit diaphragm and its axis of symmetry are aligned with the reference axis, which is defined as the line through the centre of the radiation source and parallel to the reference direction or that specified direction to which the characteristics such as target angle are referenced. The manufacturer should specify the reference axis when providing data on anode target angle and size of focal spot.

Proceedings of the British Institute of Radiology. Radionuclide investigations of the lung. Joint meeting with The Institute of Physical Sciences in Medicine Radionuclide Topic Group. London, February 11, 1987. Abstracts.

Radionuclide investigations of the lungPublished Online:29 May 2014https://doi.org/10.1259/0007-1285-60-718-1044SectionsPDF/EPUB ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InEmail AboutAbstractRespiratory complications are associated with a high proportion of the deaths from acute pancreatitis. These acute lung injuries may be associated with increased vascular permeability and may result in patients developing the adult respiratory distress syndrome. Lung vascular permeability in patients with acute pancreatitis has been investigated and the results have been related to the clinical findings.Lung permeability studies were undertaken on 16 patients with acute pancreatitis, confirmed by serum amylase levels of greater than 1000 IU/1: 10 patients had mild and six had severe transferrin radiolabelled with 113Inm was monitored over a 2 h period using a probe radiation detector, as described previously (Basran et al, 1985). Previous article Next article FiguresReferencesRelatedDetails Volume 60, Issue 718October 1987Pages: 947-B70 © The British Institute of Radiology History Published onlineMay 29,2014 Metrics Download PDF

Chernobyl – Response of Medical Physics Departments in the UK: IPSM Report No 50

J K Haywood (ed) 1986 London: IPSM xi + 99 pp price £12.75 (paperback) ISBN 0 904181 45 6 Rainwater, milk, lamb, hay, laverbread and diplomats returning from the Eastern bloc were amongst the items which arrived in UK medical physics departments for assessment after the Chernobyl accident. The Institute of Physical Sciences in Medicine (IPSM) held a one-day meeting in July to discuss the scientific aspects of the environmental and personal measurements which NHS medical physics departments were called upon to make.

Physics in Medical Ultrasound: IPSM Report No 47

This volume is described as an IPSM (Institute of Physical Sciences in Medicine) Report. It is, in fact, essentially the proceedings of a state of the art conference on medical ultrasound held in Durham in July 1985.

Meeting report: Physics in Medical Ultrasound

Report on the Institute of Physical Sciences in Medicine meeting on Physical in Medical Ultrasound held at the University of Durham, 9-10 April 1987, organized by the IPSM Ultrasonics Topic Group

Are three frequency quasiperiodic orbits to be expected in typical nonlinear dynamical systems?: 559 (M1,T3) Celso Grebogi, Laboratory for Plasma and Fusion Energy Studies, and Department of Physics and Astronomy; Edward Ott, Laboratory for Plasma and Fusion Energy Studies and Department of Electrical Engineering and Department of Physics and Astronomy; James A. Yorke, Department of Mathematics, and Institute for Physical

We achieve control of deterministic chaos in an ecosystem model, involving three first-order nonlinear differential equations with a control parameter, recently proposed by Hastings and Powell (HP) in order to describe the dynamical behavior of a three-species food chain. After identifying a chaotic attractor corresponding to a particular value of the parameter of this ecological model, we locate periodic saddle orbits embedded in it. By applying the Ott–Grebogi–Yorke (OGY) method of controlling chaos, which introduces small time-dependent perturbations on the system parameter, we stabilize two of the saddle orbits. Furthermore, we check the versatility of the OGY method, as the system behavior is allowed to switch between ‘no control’ and ‘control’ about one or other of different stabilized periodic orbits.

Estimating regions of existence of unstable periodic orbits using computer-baed techniques : Ira Bruce Schwartz, Department of Applied Mathematics and the Institute for Physical Science and Technology, University of Maryland, College Park, Maryland 20742 USA

Estimating regions of existence of unstable periodic orbits using computer-baed techniques : Ira Bruce Schwartz, Department of Applied Mathematics and the Institute for Physical Science and Technology, University of Maryland, College Park, Maryland 20742 USA