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Defining a ‘unit of harm’
219
Correspondence Letters are published at the discretion o f the Editor. Opinions expressed by correspondents are not necessarily those of the Editor. Unduly long letters may be returned to the authors for shortening. Letters in response to a paper may be sent to the author of the paper so that the reply can be published in the same issue. Letters should be typed double spaced and should be signed by all authors personally. References should be given in the style specified in the Instruction to Authors at the front of the Journal.
DEFINING A ' U N I T OF H A R M ' SIR I wrote recently indicating the need in radiology for a 'unit of h a r m ' (Russell, 1988), As no one has risen to the suggestion may I pursue the matter and propose a definition of such a unit? There are m a n y factors which m u s t be taken into account when assessing the h a r m ionising radiation causes. These include the absorbed organ doses, the perceived sensitivity to harm of the organs exposed, the age and sex of the subject, whether the subject is pregnant and the age of the pregnancy, the 'last illness factor', the number of offspring expected, and the Quality Factor of the radiation. The result can be expressed in several ways, in particular by the value of the detriment per unit dose (Russell and Webb, 1987) and, for comparison with other health spending as a value of the Quality Adjusted Life Year (or QALY) (Wall and Russell, 1988). Simple mortality rates or loss of life expectancy have also been used when cancer mortality is being considered only. Assessments such as these are not easily understood and there is a need for a simple unit of h a r m which can be used to enable radiologists, clinicians and patients to understand the possible h a r m of ionising radiation. In research we are obliged by the Declaration of Helsinki
(World Health Organisation, 1982) to inform the patient of the estimated risks of a research exposure and at present this is difficult for the researcher, the patient and for any overseeing committee. A possible definition of a 'unit of h a r m ' in radiology could be: That dose of ionising radiation which gives rise to a serious injury at the rate of one chance in a million: A serious injury in this context is a radiogenic injury giving rise to (a) death from cancer; (b) a serious congenital abnormality arising in the next generation; (c) mental deficiency arising from a fetal injury. For a given energy absorption by organs or ionising radiation the 'unit of h a r m ' will vary with the current perception of the h a r m this radiation causes so account m u s t be taken of the age/sex, expectation of children and whether the subject is pregnant and if so the state of pregnancy. Examples of the estimated 'unit of h a r m ' associated with various examinations are given in Table 1, using the effective dose equivalent and gonad absorbed dose. The unit of one in a million chance of causing death has been given for activities besides radiation exposure, and examples are given in Table 2 derived from Henderson (1987). J. G. B. R U S S E L L
St Mary's Hospital Manchester M13 OJH
Table 1
Examination
Estimated radiation dose (EDE)
Risk factor fatal cancers % Sv
Chest PA film in a 60-year-old male
0.05
1.0
A b d o m e n film in 20-year-old male
1.4
3.0
Fatal cancer risk cases /106 exams
Gonad dose (mGy)
Expectation o f children
Genetic risk* /106 exams
Total units o f harm
0.5
negligible
nil
nil
0.5
42
0.4
1.7
l1
53
Cardiac catheterisation in 55-year-old male
5.0
1.0
50
0.1
0.01
negligible
50
Barium enema in 20-year-old female
7.0
4.0
280
16
1.6
51
331
Fetal risk after99Tc brain scan in mother 18 weeks pregnant
5.5
6.0 330 5.5 1.9 + risk of mental deficiency at a rate of 0.4/Gy = 2200
20
/ ~ 2550
* Genetic risk taken as 0.20%/Gy/offspring.
Table 2 - Activities estimated to give an increase in chance of death by one in a million.
Smoking a single cigarette Risk of fatal accident at home Travel Jet travel Car travel Motorcycle travel Cycle travel
living 4 days
2500 miles 120 miles 10 miles 5 miles
Risk of fatal accident at work Vehicle manufacture Agriculture Coal Miners Deep sea fishing (before 1970)
working 1 m o n t h working 3 days working 1.5 days working one-tenth of a day
References
Henderson, M (1987). Living With RL~k. The British Medical Association Guide, John Wiley, Chichester. Russell, JGB (1988). Time for a new radiological unit o f harm? Clinical Radiology, 39, 105. Russell, JGB & Webb, G A M (1987). Valuing the man-sievert in X-ray diagnosis. British Journal o f Radiology, 60, 681 684. Wall, BF & Russell, JGB (1988). The application of cost-utility analysis to radiological protection in diagnostic radiology. Journal o f Radiologieal Protection, 8, 221-229. World Health Organisation and Council for Organisations of Medical Science (1982). Proposed international guidelines for bio-medical research involving h u m a n subjects. W H O / C I O M S , Geneva.
Correspondence Letters are published at the discretion o f the Editor. Opinions expressed by correspondents are not necessarily those of the Editor. Unduly long letters may be returned to the authors for shortening. Letters in response to a paper may be sent to the author of the paper so that the reply can be published in the same issue. Letters should be typed double spaced and should be signed by all authors personally. References should be given in the style specified in the Instruction to Authors at the front of the Journal.
DEFINING A ' U N I T OF H A R M ' SIR I wrote recently indicating the need in radiology for a 'unit of h a r m ' (Russell, 1988), As no one has risen to the suggestion may I pursue the matter and propose a definition of such a unit? There are m a n y factors which m u s t be taken into account when assessing the h a r m ionising radiation causes. These include the absorbed organ doses, the perceived sensitivity to harm of the organs exposed, the age and sex of the subject, whether the subject is pregnant and the age of the pregnancy, the 'last illness factor', the number of offspring expected, and the Quality Factor of the radiation. The result can be expressed in several ways, in particular by the value of the detriment per unit dose (Russell and Webb, 1987) and, for comparison with other health spending as a value of the Quality Adjusted Life Year (or QALY) (Wall and Russell, 1988). Simple mortality rates or loss of life expectancy have also been used when cancer mortality is being considered only. Assessments such as these are not easily understood and there is a need for a simple unit of h a r m which can be used to enable radiologists, clinicians and patients to understand the possible h a r m of ionising radiation. In research we are obliged by the Declaration of Helsinki
(World Health Organisation, 1982) to inform the patient of the estimated risks of a research exposure and at present this is difficult for the researcher, the patient and for any overseeing committee. A possible definition of a 'unit of h a r m ' in radiology could be: That dose of ionising radiation which gives rise to a serious injury at the rate of one chance in a million: A serious injury in this context is a radiogenic injury giving rise to (a) death from cancer; (b) a serious congenital abnormality arising in the next generation; (c) mental deficiency arising from a fetal injury. For a given energy absorption by organs or ionising radiation the 'unit of h a r m ' will vary with the current perception of the h a r m this radiation causes so account m u s t be taken of the age/sex, expectation of children and whether the subject is pregnant and if so the state of pregnancy. Examples of the estimated 'unit of h a r m ' associated with various examinations are given in Table 1, using the effective dose equivalent and gonad absorbed dose. The unit of one in a million chance of causing death has been given for activities besides radiation exposure, and examples are given in Table 2 derived from Henderson (1987). J. G. B. R U S S E L L
St Mary's Hospital Manchester M13 OJH
Table 1
Examination
Estimated radiation dose (EDE)
Risk factor fatal cancers % Sv
Chest PA film in a 60-year-old male
0.05
1.0
A b d o m e n film in 20-year-old male
1.4
3.0
Fatal cancer risk cases /106 exams
Gonad dose (mGy)
Expectation o f children
Genetic risk* /106 exams
Total units o f harm
0.5
negligible
nil
nil
0.5
42
0.4
1.7
l1
53
Cardiac catheterisation in 55-year-old male
5.0
1.0
50
0.1
0.01
negligible
50
Barium enema in 20-year-old female
7.0
4.0
280
16
1.6
51
331
Fetal risk after99Tc brain scan in mother 18 weeks pregnant
5.5
6.0 330 5.5 1.9 + risk of mental deficiency at a rate of 0.4/Gy = 2200
20
/ ~ 2550
* Genetic risk taken as 0.20%/Gy/offspring.
Table 2 - Activities estimated to give an increase in chance of death by one in a million.
Smoking a single cigarette Risk of fatal accident at home Travel Jet travel Car travel Motorcycle travel Cycle travel
living 4 days
2500 miles 120 miles 10 miles 5 miles
Risk of fatal accident at work Vehicle manufacture Agriculture Coal Miners Deep sea fishing (before 1970)
working 1 m o n t h working 3 days working 1.5 days working one-tenth of a day
References
Henderson, M (1987). Living With RL~k. The British Medical Association Guide, John Wiley, Chichester. Russell, JGB (1988). Time for a new radiological unit o f harm? Clinical Radiology, 39, 105. Russell, JGB & Webb, G A M (1987). Valuing the man-sievert in X-ray diagnosis. British Journal o f Radiology, 60, 681 684. Wall, BF & Russell, JGB (1988). The application of cost-utility analysis to radiological protection in diagnostic radiology. Journal o f Radiologieal Protection, 8, 221-229. World Health Organisation and Council for Organisations of Medical Science (1982). Proposed international guidelines for bio-medical research involving h u m a n subjects. W H O / C I O M S , Geneva.