1992, The British Journal of Radiology, 65, 552-556
Correspondence (The Editors do not hold themselves responsible for opinions expressed by correspondents)
Radiation protection associated with well women breast cancer screening THE EDITOR—SIR,
We wish to raise a number of issues concerning radiation protection aspects associated with well women breast cancer screening programmes now established throughout the UK. Does irradiation of well women for screening purposes constitute a medical exposure and, therefore, fall within the terms of the 1988 Ionizing Radiation (Protection of Persons Undergoing Medical Examination or Treatment) Regulations? If so, then according to section 4 part 3, persons physically directing a medical exposure shall select procedures such as to ensure a dose of ionizing radiation to the "patient" as low as reasonably parcticable in order to achieve the required diagnostic or therapeutic purpose. In the case of well women breast cancer screening what is the required diagnostic purpose and what is the upper level of dose considered acceptable to achieve this purpose? Is this the level which corresponds to a detection of 5 cancers per 1000 women on the first screen, but what about subsequent screening rounds? If irradiation of well women does not fall within the framework of the 1988 Regulations then perhaps it falls within the framework of Chapter 2 section 2.16-2.29 of the Guidance Notes to the 1985 Ionizing Radiation Regulations which is concerned with irradiation of volunteers for medical research purposes or screening programmes. In effect the UK Breast Screening Programme would be classed as a research project whose intention was to assess the riskbenefit arising from the widespread application of mammography. Obviously the well women involved are indeed volunteers. The exposure guidelines for this type of irradiation are presented in the Guidance Notes namely: wherever possible the effective dose equivalents to normal control subjects should be no greater than those for a Category II irradiation with an upper limit effective dose equivalent corresponding to dose limits for memebers of the general public. These limits are now 1 mSv. In order to evaluate the breast dose which corresponds to this dose equivalent we can employ the most recent tissue or organ weighting factor provided by ICRP for the breast, namely 0.05. However, since this figure assumes a population of both men and women, and it is predominantly females who are at risk from breast cancer, there is a strong case for taking the weighting factor to be 0.1 (see ICRP 34 p. 8). It is not at all clear, however, whether this factor constitutes a tissue or organ weighting factor. In Table B-8 of the 1990 ICRP Recommendations (Vol. 21 p. 124) the risk factor for the breast employing a multiplicative risk model is indicated as 0.6 X 102 Gy' for a population of males and females. Notwithstanding that in this publication the Tables employ units of Grays and the text refers to Sieverts, this value must be divided by 2 to calculate "the total and other organ probability values". Thus the risk per organ {i.e. to each breast) would be 0.3 X 102 Gy 1 (Sv1) which is roughly 5% of the total, all organ, risk factor quoted, namely 7 X 10 2 Gy 1 (Sv 1 ) consequently the weighting factor of 0.05 quoted above would appear to be a single organ factor and irradiation of each breast would involve an additive overall risk. This difficulty obviously
552
arises when attempting to employ organ risk factors calculated from whole body irradiation, which involves integral doses throughout a single distributed organ like red bone marrow or additive doses for multiple organs of a particular type, like the breast. Whole body irradiation will involve the whole organ (or tissue) whereas radiological irradiation will involve partial body or single organ exposure. Incidentally there is evidence in ICRP 21 Table B-14A that in the UK the relative organ risk factor for the breast might be 60% higher than the average value indicated by the organ weighting factor of 0.05 quoted above. Assuming an organ weighting factor of 0.1 for women, the maximum absorbed breast dose corresponding to the recommended upper limit for a Category II exposure of volunteers would appear to correspond to 10 mSv for the same risk as a whole body exposure of 1 mSv. If we assume a conversion factor for entrance surface dose to absorbed breast dose of approximately 0.25 for the beam qualities normally employed in mammography, then the entrance surface dose corresponding to the upper limit for Category II exposures would be 40 mGy, assuming numerical equivalence between absorbed dose and equivalent dose quantities. For a breast screening mammographic examination comprising two views per breast, the upper limit entrance surface dose would correspond to 10 mGy per image. The outputs of mammographic X-ray units are in the dose range 0.05-0.2 mGy/mAs. Consequently the upper limit X-ray exposure would correspond roughly to 100 mAs per image or 400 mAs per examination. The Commission of European Communities has issued guidelines for the upper limit entrance surface dose of 7 mGy per image for a breast examination (CEC, 1990). These guidelines were deduced from the results of a UK mammography physics group study involving approximately 30 screening centres. These measurements were not performed on actual patients but on a 4.5 cm thick Perspex phantom. Nonetheless, 25% of centres demonstrated an entrance surface dose value per image to the phantom which exceeded the value of 7.5 mGy. During the first European trial of the image quality criteria document which presented the entrance surface dose guidelines for the breast, over 25% of dose measurements made on actual patients exceeded 10 mGy per image. There is no evidence to indicate that the situation within the UK is any different. If this is the case then up to 25% of women undergoing mammographic breast screening examination comprising two views of each breast may be receiving a dose which exceeds the upper limit for a Category II exposure of volunteers. At this level of exposure the benefit/risk ratio expressed in terms of cancers detected to cancers induced for a women 50-54 years of age would be approximately 50 for a single screen, with a lifetime benefit/risk decreasing markedly with subsequent screens. A number of questions obviously need to be addressed. 1. What is the precise radiation protection frame work which covers the exposure of well women in breast screening programmes? 2. What are the actual levels of radiation being employed as distinct from measurements employing phantoms? 3. Why have Perspex phantom measurements been employed in assessing actual breast doses when this approach is not employed for other radoilogical examinations?
The British Journal of Radiology, June 1992
Correspondence 4. What constitutes an acceptable upper limit dose for an examination? 5. What action needs to be taken and by whom if any upper limit is exceeded? 6. What are acceptable benefit-risk ratios for well women screening? 7. Are there particular groups within the population, i.e. women with large and/or dense breasts who should be considered sepa' rately? 8. If women continue to receive doses from multiple screening rounds what is an acceptable lifetime benfit-risk ratio? 9. What are the specific diagnostic purposes in an ongoing breast screening programme? 10. To whom should these questions be addressed? A great deal of material has been published in both the popular press and scientific journals extolling the virtues of breast screening programmes for the early detection of cancer. However, it would appear that a number of fundamental radiation protection aspects have not yet been resolved. Their resolution would help greatly in providing a balanced appraisal of the acceptable levels of risks arising from breast screening programmes employing mammography. Hopefully this letter will prompt further discussion on these issues. Yours etc., B. M. MOORES E. T. HENSHAW
Integrated Radiological Services Ltd, Unit 188, Centuary Building, 102 Tower Street, Liverpool L3 4BJ (Received 29 January 1992, accepted 8 April 1992) References CEC, 1990. Quality Criteria for Diagnostic Radiographic Images, 2nd edn (Brussels).
THE EDITOR—SIR,
F. Wright's comments further consolidate my point that simulator radiographs should not be used for diagnostic purposes and the expertise of radiologists is essential to give a broader differential diagnosis. However, with respect, the mass in question, seen on the supine but not the erect radiographs, was in the anterio-posterior (AP) projected region of the right hilum. As the title suggested this may have been "mistaken" for a hilar mass without further lateral or barium studies. In a man with a long history of severe oesophageal reflux, oesophageal dilation in the posterior mediastinum is by far the most likely diagnosis. A soft tissue chest wall mass or prominent pulmonary vessels are less likely to demonstrate such dramatic postural changes. Oesphageal dilation in the differential diagnosis of paramediastinal radiographic masses is well established (Grainger, 1980; Hoffner, 1989) and is often discussed in medical teaching sessions and, hence, although not common is well known. Yours etc., R. J. THOMAS
Department of Oncology, University College London, The Middlesex Hospital, London WIN 8AA (Received 7 February 1992, accepted 8 April 1992) References GRAINGER, R., 1980. Textbook of Radiology and Imaging, ed. by D. Sutton, 3rd edn (Churchill Livingstone, Eastbourne), p. 444. HOFFNER, J., 1989. Textbook of Internal Medicine, ed. by W. Kelley, p. 1960.
Results from the HAD psychometric questionnaire in 54 breast cancer patients treated with breast conservation
Mistaken hilar mass THE EDITOR—SIR,
R. Thomas discusses the possibility of hilar enlargement due to a dilated oesophagus on a supine radiograph taken on a radiotherapy simulator apparatus and states that this is "well known"! Two radiographs, one supine and one in the erect position were published with his letter to "prove" the point. However, the oesophagus is not a hilar structure as it lies behind it, and in the absence of a barium examination showing a mid-oesophageal diverticulum lying behind the hilum, I find the explanation very difficult to believe. Two likely explanations are: (a) the soft tissue mass of the chest wall tumour being treated; or more likely (b) the right venous confluence of the pulmonary veins where this joins the left atrium. Yours etc., F. W. WRIGHT
X-ray Department, The Churchill Hospital, Oxford OX3 7LJ (Received 20 January 1992, accepted 8 April 1992) Reference THOMAS, R., 1991. Mistaken hilar mass. British Journal of Radiology, 64, 977.
Vol. 65, No 774
Author's reply
THE EDITOR—SIR,
Following the report in this journal by Bull and Campbell (1991) on the use of the HAD psychometric scale to detect anxiety and depression in women attending for breast screening which turned out to be negative, it may be of interest to compare the results with those obtained in patients with established breast cancer. 57 patients with operable breast cancer presented in 1 year to a single surgical firm at the Westminster Hospital and were treated by uniform breast conservation policy (Bulman et al, 1987). 54 completed the HAD scale after local tumour excision, after radical radiotherapy, at 6 months and at 12 months. Standard criteria were used for normal, borderline and abnormal scores. Mean scores, range of scores and the proportion of patients with borderline and abnormal scores are shown in Table I for anxiety and Table II for depression. A total of 15 out of 54 patients scored abnormally anxious at least once, four of these 15 patients scored both abnormally anxious and depressed. There were no cases of depression without anxiety. All 54 patients were also interviewed by a senior consultant psychiatrist at 6 months. One of the 15 patients with an abnormal HAD score received psychiatric treatment, as did one other patient who did not score as abnormal or borderline on HAD. This treatment rate was lower than we had anticipated based on more
553
Correspondence (The Editors do not hold themselves responsible for opinions expressed by correspondents)
Radiation protection associated with well women breast cancer screening THE EDITOR—SIR,
We wish to raise a number of issues concerning radiation protection aspects associated with well women breast cancer screening programmes now established throughout the UK. Does irradiation of well women for screening purposes constitute a medical exposure and, therefore, fall within the terms of the 1988 Ionizing Radiation (Protection of Persons Undergoing Medical Examination or Treatment) Regulations? If so, then according to section 4 part 3, persons physically directing a medical exposure shall select procedures such as to ensure a dose of ionizing radiation to the "patient" as low as reasonably parcticable in order to achieve the required diagnostic or therapeutic purpose. In the case of well women breast cancer screening what is the required diagnostic purpose and what is the upper level of dose considered acceptable to achieve this purpose? Is this the level which corresponds to a detection of 5 cancers per 1000 women on the first screen, but what about subsequent screening rounds? If irradiation of well women does not fall within the framework of the 1988 Regulations then perhaps it falls within the framework of Chapter 2 section 2.16-2.29 of the Guidance Notes to the 1985 Ionizing Radiation Regulations which is concerned with irradiation of volunteers for medical research purposes or screening programmes. In effect the UK Breast Screening Programme would be classed as a research project whose intention was to assess the riskbenefit arising from the widespread application of mammography. Obviously the well women involved are indeed volunteers. The exposure guidelines for this type of irradiation are presented in the Guidance Notes namely: wherever possible the effective dose equivalents to normal control subjects should be no greater than those for a Category II irradiation with an upper limit effective dose equivalent corresponding to dose limits for memebers of the general public. These limits are now 1 mSv. In order to evaluate the breast dose which corresponds to this dose equivalent we can employ the most recent tissue or organ weighting factor provided by ICRP for the breast, namely 0.05. However, since this figure assumes a population of both men and women, and it is predominantly females who are at risk from breast cancer, there is a strong case for taking the weighting factor to be 0.1 (see ICRP 34 p. 8). It is not at all clear, however, whether this factor constitutes a tissue or organ weighting factor. In Table B-8 of the 1990 ICRP Recommendations (Vol. 21 p. 124) the risk factor for the breast employing a multiplicative risk model is indicated as 0.6 X 102 Gy' for a population of males and females. Notwithstanding that in this publication the Tables employ units of Grays and the text refers to Sieverts, this value must be divided by 2 to calculate "the total and other organ probability values". Thus the risk per organ {i.e. to each breast) would be 0.3 X 102 Gy 1 (Sv1) which is roughly 5% of the total, all organ, risk factor quoted, namely 7 X 10 2 Gy 1 (Sv 1 ) consequently the weighting factor of 0.05 quoted above would appear to be a single organ factor and irradiation of each breast would involve an additive overall risk. This difficulty obviously
552
arises when attempting to employ organ risk factors calculated from whole body irradiation, which involves integral doses throughout a single distributed organ like red bone marrow or additive doses for multiple organs of a particular type, like the breast. Whole body irradiation will involve the whole organ (or tissue) whereas radiological irradiation will involve partial body or single organ exposure. Incidentally there is evidence in ICRP 21 Table B-14A that in the UK the relative organ risk factor for the breast might be 60% higher than the average value indicated by the organ weighting factor of 0.05 quoted above. Assuming an organ weighting factor of 0.1 for women, the maximum absorbed breast dose corresponding to the recommended upper limit for a Category II exposure of volunteers would appear to correspond to 10 mSv for the same risk as a whole body exposure of 1 mSv. If we assume a conversion factor for entrance surface dose to absorbed breast dose of approximately 0.25 for the beam qualities normally employed in mammography, then the entrance surface dose corresponding to the upper limit for Category II exposures would be 40 mGy, assuming numerical equivalence between absorbed dose and equivalent dose quantities. For a breast screening mammographic examination comprising two views per breast, the upper limit entrance surface dose would correspond to 10 mGy per image. The outputs of mammographic X-ray units are in the dose range 0.05-0.2 mGy/mAs. Consequently the upper limit X-ray exposure would correspond roughly to 100 mAs per image or 400 mAs per examination. The Commission of European Communities has issued guidelines for the upper limit entrance surface dose of 7 mGy per image for a breast examination (CEC, 1990). These guidelines were deduced from the results of a UK mammography physics group study involving approximately 30 screening centres. These measurements were not performed on actual patients but on a 4.5 cm thick Perspex phantom. Nonetheless, 25% of centres demonstrated an entrance surface dose value per image to the phantom which exceeded the value of 7.5 mGy. During the first European trial of the image quality criteria document which presented the entrance surface dose guidelines for the breast, over 25% of dose measurements made on actual patients exceeded 10 mGy per image. There is no evidence to indicate that the situation within the UK is any different. If this is the case then up to 25% of women undergoing mammographic breast screening examination comprising two views of each breast may be receiving a dose which exceeds the upper limit for a Category II exposure of volunteers. At this level of exposure the benefit/risk ratio expressed in terms of cancers detected to cancers induced for a women 50-54 years of age would be approximately 50 for a single screen, with a lifetime benefit/risk decreasing markedly with subsequent screens. A number of questions obviously need to be addressed. 1. What is the precise radiation protection frame work which covers the exposure of well women in breast screening programmes? 2. What are the actual levels of radiation being employed as distinct from measurements employing phantoms? 3. Why have Perspex phantom measurements been employed in assessing actual breast doses when this approach is not employed for other radoilogical examinations?
The British Journal of Radiology, June 1992
Correspondence 4. What constitutes an acceptable upper limit dose for an examination? 5. What action needs to be taken and by whom if any upper limit is exceeded? 6. What are acceptable benefit-risk ratios for well women screening? 7. Are there particular groups within the population, i.e. women with large and/or dense breasts who should be considered sepa' rately? 8. If women continue to receive doses from multiple screening rounds what is an acceptable lifetime benfit-risk ratio? 9. What are the specific diagnostic purposes in an ongoing breast screening programme? 10. To whom should these questions be addressed? A great deal of material has been published in both the popular press and scientific journals extolling the virtues of breast screening programmes for the early detection of cancer. However, it would appear that a number of fundamental radiation protection aspects have not yet been resolved. Their resolution would help greatly in providing a balanced appraisal of the acceptable levels of risks arising from breast screening programmes employing mammography. Hopefully this letter will prompt further discussion on these issues. Yours etc., B. M. MOORES E. T. HENSHAW
Integrated Radiological Services Ltd, Unit 188, Centuary Building, 102 Tower Street, Liverpool L3 4BJ (Received 29 January 1992, accepted 8 April 1992) References CEC, 1990. Quality Criteria for Diagnostic Radiographic Images, 2nd edn (Brussels).
THE EDITOR—SIR,
F. Wright's comments further consolidate my point that simulator radiographs should not be used for diagnostic purposes and the expertise of radiologists is essential to give a broader differential diagnosis. However, with respect, the mass in question, seen on the supine but not the erect radiographs, was in the anterio-posterior (AP) projected region of the right hilum. As the title suggested this may have been "mistaken" for a hilar mass without further lateral or barium studies. In a man with a long history of severe oesophageal reflux, oesophageal dilation in the posterior mediastinum is by far the most likely diagnosis. A soft tissue chest wall mass or prominent pulmonary vessels are less likely to demonstrate such dramatic postural changes. Oesphageal dilation in the differential diagnosis of paramediastinal radiographic masses is well established (Grainger, 1980; Hoffner, 1989) and is often discussed in medical teaching sessions and, hence, although not common is well known. Yours etc., R. J. THOMAS
Department of Oncology, University College London, The Middlesex Hospital, London WIN 8AA (Received 7 February 1992, accepted 8 April 1992) References GRAINGER, R., 1980. Textbook of Radiology and Imaging, ed. by D. Sutton, 3rd edn (Churchill Livingstone, Eastbourne), p. 444. HOFFNER, J., 1989. Textbook of Internal Medicine, ed. by W. Kelley, p. 1960.
Results from the HAD psychometric questionnaire in 54 breast cancer patients treated with breast conservation
Mistaken hilar mass THE EDITOR—SIR,
R. Thomas discusses the possibility of hilar enlargement due to a dilated oesophagus on a supine radiograph taken on a radiotherapy simulator apparatus and states that this is "well known"! Two radiographs, one supine and one in the erect position were published with his letter to "prove" the point. However, the oesophagus is not a hilar structure as it lies behind it, and in the absence of a barium examination showing a mid-oesophageal diverticulum lying behind the hilum, I find the explanation very difficult to believe. Two likely explanations are: (a) the soft tissue mass of the chest wall tumour being treated; or more likely (b) the right venous confluence of the pulmonary veins where this joins the left atrium. Yours etc., F. W. WRIGHT
X-ray Department, The Churchill Hospital, Oxford OX3 7LJ (Received 20 January 1992, accepted 8 April 1992) Reference THOMAS, R., 1991. Mistaken hilar mass. British Journal of Radiology, 64, 977.
Vol. 65, No 774
Author's reply
THE EDITOR—SIR,
Following the report in this journal by Bull and Campbell (1991) on the use of the HAD psychometric scale to detect anxiety and depression in women attending for breast screening which turned out to be negative, it may be of interest to compare the results with those obtained in patients with established breast cancer. 57 patients with operable breast cancer presented in 1 year to a single surgical firm at the Westminster Hospital and were treated by uniform breast conservation policy (Bulman et al, 1987). 54 completed the HAD scale after local tumour excision, after radical radiotherapy, at 6 months and at 12 months. Standard criteria were used for normal, borderline and abnormal scores. Mean scores, range of scores and the proportion of patients with borderline and abnormal scores are shown in Table I for anxiety and Table II for depression. A total of 15 out of 54 patients scored abnormally anxious at least once, four of these 15 patients scored both abnormally anxious and depressed. There were no cases of depression without anxiety. All 54 patients were also interviewed by a senior consultant psychiatrist at 6 months. One of the 15 patients with an abnormal HAD score received psychiatric treatment, as did one other patient who did not score as abnormal or borderline on HAD. This treatment rate was lower than we had anticipated based on more
553
