| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
Correspondence |
In a paper on the mortality of British radiologists over the 100 years from 1897 to 1997, we reported that the mortality of those who had registered since 1954 was remarkably low in comparison with that of medical practitioners as a whole [1]. This was true both for cancer (SMR 0.71, 32 deaths against 45.03 expected, p=0.052) and for all other causes of death combined (SMR 0.64, 77 deaths against 20.66 expected, p<0.001). This low mortality, we said, "is likely to be at least partly owing to the healthy worker effect not yet having completely worn off, as the group has not been followed up for as long as the other cohorts" (that is, those who had qualified in earlier periods). We did not discuss the findings further; but others subsequently have. Cameron [2] suggested that the reason might be that a "moderate dose rate" from ionizing radiation was not harmful, and Simmons [3] said that our finding challenges the generally accepted belief "that the cancer risk from low doses of X-rays or gamma-rays decreases linearly with decreasing dose". It seemed, therefore, that a more detailed examination of the possible reasons for our finding of low mortality might be desirable.
Chance and a healthy worker effect may have contributed to the low mortality, but are unlikely to have caused as big a difference as was actually observed. No internal comparison group was possible, so in our study we compared the death rates of the male radiologists with those experienced by all men in the country, all men in social class 1 and estimates for all male medical practitioners, respectively. Medical practitioners are certainly more suitable than all men in the first two groups, but even so they may not have provided an appropriate norm. Specialists, for example, tend to have lower mortality rates than general practitioners [4] and all medical specialists might have been more appropriate. National figures for specialists were not available. Some figures have, however, been provided by Carpenter et al [5] for doctors in different specialties working in the National Health Service in England and Wales. The standardized mortality rates (SMR) for male specialists aged 25–74 years in comparison with those for all men in England and Wales were, respectively, 0.45 for all neoplasms (based on 730 deaths 95% confidence limits 0.42 to 0.49) and by subtraction from all deaths, 0.48 for all other causes. These rates are almost identical to the SMRs we observed in comparison with all men of 0.46 for all cancer deaths and 0.49 for all non-cancer deaths.
Radiologists within the cohort of Carpenter et al [5], moreover, had rates almost identical to those of all specialists as a whole, the relative risk for malignant neoplasms being 0.99 and for all other causes (by subtraction) 1.04. Clearly there is no reason to suppose that the mortality of radiologists was any different from that of specialists in general or that there was anything about their job which per se provided any specific benefit to health, a conclusion that was also reached by Matanoski et al [6] when they compared the mortality of radiologists with that of other physician specialists in the USA.
Why medical specialists should have such relatively low risks of mortality is unclear. One reason is that they have had a particularly low prevalence of smoking, as was shown by Doll and Peto [4] when they examined the mortality of 12 occupational groups of doctors within the cohort whose smoking habits had been determined in 1951 and again in 1971. Specialists were found to have smoked substantially less than general practitioners, while all British doctors smoked less than the general population [7]. Other factors, however, are likely also to have played a part, including those that cause low rates for men and women in the higher social classes and, to a small extent, the factors that contributed to a relatively low mortality in working populations in general [8].
We conclude that the low mortality of British radiologists who were registered in the period 1955–1997, in comparison with that for all medical practitioners, is attributable to the factors that cause a relatively low mortality in doctors in all medical specialties. There is no reason to attribute it to a specific benefit from exposure to low doses of ionizing radiation.
Yours etc.,
1 Cancer Research UK/MRC/BHF Clinical Trial Service Unit and Epidemiological Studies Unit, 2 Cancer Research UK Epidemiology Unit, Richard Doll Building, Old Road Campus, Rocsevelt Drive Oxford Ox3 7LF, UK
Received for publication January 8, 2004. Revision received May 6, 2005. Accepted for publication June 1, 2005.
References
This article has been cited by other articles:
 |
|
 |
|
  BJR Review of the Year - 2005. Br. J. Radiol., March 1, 2006; 79(939): 183 - 187. [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| BJR | DMFR | IMAGING | ALL BIR JOURNALS |
