Occupational Exposure
There are several groups of people occupationally exposed to ionising radiation. This includes workers in the nuclear industry (mining, reactors etc) and those in medicine (nuclear medicine, radiology and radiation oncology).
For workers in the nuclear industry, there is no evidence of a statistically significant risk of cancers unless those from the Soviet Union are considered. This is achievable by following the ICRP guidelines on radiation exposure. There was a trend to increased risk of leukaemia in UK workers but a negative risk in US workers; the risks for solid cancers approach zero.
Radiologists working prior to 1950 have an elevated risk of carcinogenesis. This has not continued in the era of effective radiation protection, where an elevated risk is not detectable on retrospective studies.
Medical Exposure
Diagnostic Radiation
The risks established by the ICRP with relation to carcinogenesis are:
- 5% risk (per Sv) of fatal cancer
- 0.9% risk (per Sv) of non-fatal cancer
- 0.2% risk (per Sv) of hereditary effects
By calculating the amount of person-Sv the population receives, it is therefore possible to estimate the numbers of fatal malignancies induced by diagnostic procedures. However, the population receiving these x-rays is typically older and less likely to develop a stochastic malignancy.
Interventional Radiology
Interventional procedures typically deliver a higher dose than diagnostic procedures due to the use of fluoroscopy. The population undergoing these procedures is also typically older than the average population, reducing the risks of developing a stochastic malignancy.
Therapeutic Radiation
As discussed in the Carcinogenesis after radiation exposure section, there is debate about the risks of radiation following treatment for malignancy. Analysis of these risks is made difficult by the increased rate of malignancy that would be expected in these patients due to the genetic and environmental factors that caused their original cancer.
There is evidence from Hodgkin's cancer survivors that a dose-response relationship exists with relation to carcinogenesis. Women who received the highest doses of radiation through the breast had an 8-fold higher incidence of breast cancer than those who had the lowest. Patients who survive treatments of which prophylatic cranial irradiation plays a role show an increased risk of glioma and meningioma.
The magnitude of this risk is thought to perhaps plateau after a certain dose is reached, but the exact figures are hard to establish.
Military Exposure
There are two common routes of military exposure:
- Weapons containing depleted uranium (high mass allows penetration of armoured targets)
- Nuclear weapons (in which case we'll probably all be dead anyway, so carcinogenesis is less of a concern)
Depleted uranium has been used in several conflicts (Iraq, Afghanistan). For a discussion, look here. There is minimal evidence in humans injured with depleted uranium munitions; however studies of mice implanted with depleted uranium show a much higher rate of leukaemia.
Work is continuing on measures to prevent radiation induced malignancy from military exposure of ionising radiation.
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