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ABSTRACT: In order to discuss the balance of benefit and radiation risk in a breast screening programme, it is necessary to have numerical values for the probability of breast cancer induction by X-rays, stratified by age. Various sets of such values have been used hitherto, mainly in relation to breast screening in the UK, both within the NHS Screening Programme and more generally for younger age groups. Further sets have recently been reported. These different sets of values are described and discussed, together with the effects of using additive or relative risk models, and the effect of using a dose and dose rate modifying factor (DDREF). Possible new radiation risk factors for breast cancer induction by X-rays, drawn from these sets, are identified. These are used to calculate fresh values of cancer detection/induction ratios, as an index of benefit/risk, for screening age women and for younger women with and without a family history of breast cancer.
The British journal of radiology 05/2007; 80(952):261-6. · 2.11 Impact Factor
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The British journal of radiology 11/2006; 79(946):851-2; author reply 852-4. · 2.11 Impact Factor
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J Law
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ABSTRACT: This review traces the development of mammography physics over the last 50 years, concentrating mainly on technological changes and their inter-relations. It has been written for physicists with no specific mammography experience but a general interest in radiology, as much as for those with recent involvement in mammography. Topics covered include industrial film, xerography, intensifying screens, x-ray tube developments, image quality test objects, patient dose and performance checks. Some of these developments were necessary before population screening of healthy women could be considered, while others have resulted from increased opportunities for equipment manufactures which screening programmes created. The standpoint of this review is that of a physicist with long experience in a UK centre where mammography was performed on dedicated equipment well over 40 years ago and where screening has been performed continuously for 30 years.
Physics in Medicine and Biology 08/2006; 51(13):R155-67. · 2.83 Impact Factor
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ABSTRACT: The balance between benefit and radiation risk in a breast cancer screening programme has received much attention at the initial screening stage. This paper extends that attention to first stage assessment, i.e. the first stage at which women are recalled for further investigation because of suspected lesions or other suspect film features, and prior to any biopsy. Numbers of films, including magnification films, taken at this stage, have been established in two UK regions by different methods. Average total mean glandular dose has been calculated using published data of dose per film from initial screening and a multiplying factor to allow for magnification film dose. It is concluded that the benefit/risk ratio is considerably higher at first stage assessment than at initial screening by a factor of between 4 and 9, because of the very much higher cancer detection rate in this well-defined sub-group of women. Qualitatively, this conclusion is unaffected by the quite wide variation between screening centres in the numbers of films taken at first stage assessment.
British Journal of Radiology 07/2006; 79(942):479-82. · 1.31 Impact Factor
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J Law
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ABSTRACT: In mammography, much attention has been given to estimating breast dose from exposures made in conventional "contact" geometry, but much less attention has been given to doses from magnification geometry. Estimation based on contact film dose is difficult because the grid is removed, the geometry is different, and calculation of scatter reaching the film is complex. In this paper, exposures of Perspex blocks of standard thickness to give the same film density in both geometries are compared on 20 X-ray sets of various designs with a nominal magnification 1.8. The ratio derived between doses in each geometry is 2.2+/-0.15, giving an average magnification film dose of 5.0+/-0.3 mGy.
British Journal of Radiology 10/2005; 78(933):816-20. · 1.31 Impact Factor
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ABSTRACT: In screening of a general population for breast cancer, benefit/risk ratios are of the order of 100/1. For the very small subgroup of women treated by radiotherapy for Hodgkin's disease below age 35, calculations of this type require different considerations, an overview of which is given in this text. It is concluded that although such previous exposures will increase their radiation risk, their increased risk of carrying an undetected breast cancer means that the potential benefit for them of screening is increased even more. In the United Kingdom, the Department of Health has recommended annual screening for these women.
Radiation Protection Dosimetry 02/2005; 117(1-3):330-3. · 0.82 Impact Factor
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ABSTRACT: The UK Breast Screening Programme intends to introduce two-view screening on all screening rounds, and also to extend the normal screening age range at its upper end from the present 64 years to 70 years. The implications of these changes for cancer detection:induction ratios and for benefit/risk ratios are discussed. It is shown that both ratios remain much greater than 1.0 at all screening ages. This is also true for younger women, subject to provisos regarding starting ages for annual screening as described in previous papers. The requirements for optimization in a breast screening programme are also discussed. It is suggested that benefit (rather than the benefit/risk ratio) should be maximized provided that benefit exceeds risk.
British Journal of Radiology 12/2002; 75(899):889-94. · 1.31 Impact Factor
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ABSTRACT: In a breast screening programme based upon X-ray mammography it is necessary to demonstrate that benefit, from reduced mortality arising from earlier diagnosis, exceeds any potential risk from future induction of breast cancers by ionizing radiation. A rigorous treatment of this problem would be both complex and subject to large statistical uncertainty, even if all necessary data were available. A more simplified approach is to show that the number of cancers detected exceeds the number potentially induced by a sufficient margin. These numbers are relatively well established, but this approach is less satisfactory owing to the question of what would constitute a sufficient margin. This paper attempts to explore a possible relationship between the detection/induction ratio and the benefit/risk ratio, using treatment outcome data from three independent sources and mortality reduction data. Agreement between these four sources is considered to be fair, given the nature of the data. The future screening of older women (over 65 years) is also found to have a significant effect on the final outcome. When current trends in such screening are allowed for, the benefit/risk ratio is found to be only marginally less than the detection/induction ratio.
British Journal of Radiology 09/2002; 75(896):678-84. · 1.31 Impact Factor
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ABSTRACT: Current cancer detection rates and dose levels in the UK Breast Screening Programme are used to compare numbers of cancers detected with numbers predicted to be induced by the screening process itself. Numbers of those detected are shown to exceed those induced by a large margin for women aged over 50 years. The associated benefit/risk ratio is also considered. For younger women this margin is progressively reduced but remains positive at least down to age 40 years, and possibly beyond. Women both with and without a family history of breast cancer are considered. Some implications for familial breast screening programmes are discussed. Some caution may be required before annual screening of women below the age of 35 years.
British Journal of Radiology 01/2002; 74(888):1121-7. · 1.31 Impact Factor
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J Law
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ABSTRACT: Image quality has been assessed using three different phantoms on 28 mammographic X-ray units in the National Health Service Breast Screening Programme within the UK. The results show only relatively minor differences between different models of X-ray unit and between the 14 associated film processors, but more marked differences between different film-screen combinations. Medium screens give significantly lower image quality scores than fine screens from the same manufacturer. It is suggested that, to improve mammographic image quality, a change of screen type may bring greater benefit than a change of X-ray set model, as well as being much more cost effective.
British Journal of Radiology 11/1997; 70(839):1131-8. · 1.31 Impact Factor
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J Law
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ABSTRACT: The numbers of cancers detected and induced in breast screening programmes are examined for two-view screening, and for a 2 year screening interval, in contrast to the single view screening at a 3 year interval of the UK Breast Screening Programme up until early 1995. Two-view screening is also considered for the 1 year interval and age range of the current UK age trial (40-47 years). The corresponding figures for screening of groups having a family history of breast cancer are calculated and discussed. Breast cancer induction data are taken from National Radiological Protection Board publications. Cancer detection rates are based on observed rates where available, and calculated rates otherwise. The results of calculations indicate cause for concern if screening is to be extended below the age of 30 years (or below 35 years in certain categories), or below 40 years of age if family history groups are shown in the future to have a generally increased susceptibility to ionizing radiation. The importance of restricting dose to 2 mGy per film (mean glandular dose for a standard breast thickness of 4.5 cm) is stressed, together with the need ot maintain maximum image quality. This is especially true for the family history groups, who should only be screened in centres within established screening programmes, or in centres with equally strict quality control procedures.
British Journal of Radiology 02/1997; 70:62-9. · 1.31 Impact Factor
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J Law
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ABSTRACT: Maintaining a constant and appropriate mean film optical density in mammography is an essential part of quality assurance in a breast screening programme. It depends on stability in X-ray exposure controls, film supplies, intensifying screens and film processing. A programme of weekly monitoring is described which helps to trace the source of any irregular or step-wise changes in any of the relevant parameters. Its results are also used to investigate by statistical methods the degree of film optical density variation achieved in periods of several weeks of apparent general stability. Results are presented for 20 X-ray sets and a total of 32 record periods of 8-10 weeks each. The mean standard deviation for density of a single film of a Perspex block was found to be 3.5%. For processor speed index it was the same while for X-ray set variations it was less than 2%. Neither of these last two variables showed any strong correlation with block film optical density.
British Journal of Radiology 05/1996; 69(820):306-10. · 1.31 Impact Factor
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J Law
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ABSTRACT: Quality control procedures in relation to speed and contrast in X-ray film processors, both in X-ray departments and breast screening centres, are based on the use of film sensitometers. Calibrations of these instruments, or simple checks of their constancy with time, are not readily available. A procedure is described in which a reference sensitometer is compared on a 3-monthly basis with the local sensitometer in seven breast screening centres (13 processors) in a region. This demonstrated long-term stability of speed and contrast in both sensitometers and processors. The results may also be used to compare speed and contrast between processors in centres using film of a single type. Standard deviations for single measurements are estimated to be approximately 1% for step density on a single sensitometer, less than 3% for comparison of two sensitometers, about 6% for comparison of processor speed, and between 4 and 5% for processor contrast.
British Journal of Radiology 03/1996; 69(818):143-7. · 1.31 Impact Factor
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J Law
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ABSTRACT: This paper discusses and attempts to estimate the very small numbers of women attending the UK Breast Screening Programme for whom the risk of cancer induction may exceed the probability of cancer detection. It updates a previous paper on the same topic. Variations in breast dose between individuals, due to differences in breast size and in numbers of views and films taken, are considered and revised. New data on cancer induction and its variation with age at exposure have been employed. The overall effect of these changes is generally to improve the balance of benefit against risk compared with the previous paper referred to, the very few exceptions being categories where the numbers of women in question remain of the order of one in a million. The implications for certain alternative screening schedules and for some current trials are also discussed, the conclusions being again reasonably reassuring.
British Journal of Radiology 09/1995; 68(812):870-6. · 1.31 Impact Factor
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ABSTRACT: 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.
British Journal of Radiology 09/1995; 68(812):877-81. · 1.31 Impact Factor
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ABSTRACT: Mean glandular dose in mammography may be deduced from measurements made using Perspex blocks. This method is almost universally used in the National Health Service Breast Screening Programme. The effect on the estimated mean glandular dose of variations in the measured thickness of Perspex from a nominal thickness of 40 mm was investigated. Results are presented from three UK Regions. Variations in measured Perspex thicknesses ranged from almost 8% below to about 2% above the 40 mm nominal, causing errors in dose estimation, if uncorrected, of about +20% to -6.5%. A means of correcting dose estimates for measured differences in block thickness is presented. An alternative method of ensuring consistent dosimetry would be to use accurately machined Perspex blocks.
British Journal of Radiology 03/1995; 68(806):194-6. · 1.31 Impact Factor
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ABSTRACT: It is important to establish and maintain high standards of image quality in mammography in order to detect breast cancer at an early stage. A commonly used method of assessing image quality in mammography is to use test phantoms. This paper reports a comparison of seven mammographic phantoms. These are the Ackermann (DuPont, Stevenage), Barts (White and Tucker), CIRS XI (Computerized Imaging Reference Systems, USA), Leeds TOR(MAX) and Leeds TOR(MAM) (Faxil, Leeds), Newcastle, and RMI 152 (Gammex RMI, Nottingham). These phantoms were assessed on the detectability of the various details and bar patterns contained in each. Step wedges and simulated anatomical features were not assessed. The effect on phantom images of changes in contrast, caused by changing tube potential from 25 kV to 35 kV, and of changes in resolution, caused by different focal spot sizes and by different magnifications, were investigated. It was deduced from the results of this study that there was no single phantom which was clearly superior to all the others. The three phantoms which had the greatest sensitivity to changes in imaging parameters were the Leeds TOR(MAM), the Newcastle and the Ackermann (DuPont) phantoms.
British Journal of Radiology 03/1994; 67(794):174-80. · 1.31 Impact Factor
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J Law
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ABSTRACT: In a breast screening programme there is a small but inevitable risk of inducing some breast cancers that may appear many years later. This risk has to be compared with the benefits of detecting existing cancers at an early stage. In the current UK screening programme, for women aged 50-64 years and with a 3-year screening interval, the numbers detected greatly exceed the numbers predicted to be induced. For the individual, only those with very large and thick breasts who also have many views taken during the screening process appear to be at any appreciable risk, and the number for whom the risk of induction exceeds the probability of cancer detection is of the order of less than 1 per million, a risk level normally considered negligible. Results are also presented for younger age groups, and for a range of dose levels. Down to age 35 years, induction exceeds detection in less than about 1% of those screened, if a 3-yearly interval is maintained. The effect of shorter screening intervals is briefly considered. All results are based on repeat screening rounds (incidence rounds) using a single view and not on the initial (prevalence) round, and use UK data for breast cancer incidence. The calculation requires a number of assumptions and is intended as a preliminary one, pending more data on doses and numbers of women requiring specific numbers of films in screening programmes, but sufficient to promote discussion of the appropriate age range for breast screening.
British Journal of Radiology 09/1993; 66(788):691-8. · 1.31 Impact Factor
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J Law
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ABSTRACT: This paper reports an experimental investigation of the extent to which focal spot size influences image resolution in mammography. Films of two different phantoms, both containing high contrast bar patterns, were obtained using three different foci from 0.9 to 0.1 mm, and three degrees of magnification with the smallest of those foci. Some influence of focal spot size was detectable in all films except for the 0.1 mm focus at low magnification, where it was negligible in comparison with film-screen unsharpness, but effects attributed to the film-screen system were more important than focus size except with the 0.9 mm focus or at high magnification. However, a nominal 0.4 mm focus may have an effective size of 0.9 mm close to the chest wall side of the film. These two phantoms, and two others, were used to investigate the changes of perceptibility of "realistic" details, all of which depend on a combination of contrast, resolution and noise, with changes of focal spot size and magnification. As expected, when judged in this way image quality improved as focal spot size decreased. With the fine focus it also improved as magnification increased, unlike changes in high contrast resolution which decreased for high magnification. Thus conventional bar patterns are not always a good guide to detail perceptibility in mammograms, where the effects of noise may be as important as those of focal spot size.
British Journal of Radiology 06/1993; 66(785):441-6. · 1.31 Impact Factor
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J Law
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ABSTRACT: Three different measurement techniques for estimating the size of focal spots in X-ray tubes are described. These are the pin-hole, the slit and the star pattern or resolution pattern, and all are well known. Results are reported for a number of modern mammography X-ray tubes employed in a screening programme, using all three techniques. The results are compared with each other and with makers' specifications, IEC tolerances and UK Department of Health guidelines. Agreement between slit and star pattern results is generally within a few per cent, while pin-hole results are usually appreciably smaller. Although the slit technique is the most reliable for estimating focal spot size, both the others have a useful role, especially in revealing focal spot condition. Compliance with makers' specifications is usually demonstrated, but compliance with Department of Health guidelines is only found on the width of broad foci.
British Journal of Radiology 02/1993; 66(781):44-50. · 1.31 Impact Factor
