The kind of threat posed by low doses of ionising radiation is still not yet conclusively well known. New studies are further fuelling the scientific controversy.
Maria Grazia Andreassi from Pisa recently surveyed doctors and their assistants who work in the cardiac catheter lab. Physicians do indeed wear lead protection as a shield against radiation. Their arms, neck and head are not covered though and could, according to one thesis, suffer damage. The researcher collected information by way of a questionnaire which detailed how many X-ray interventions took place per person. She also wanted to know whether physical ailments occurred. At the same time Andreassi worked with a control group from hospitals where no radiation exposure was involved. Factors such as age, gender and nicotine consumption were also taken into account. The effective dose was estimated at 21 mSv (cardiologists) and 7 mSv (nurses or assistants).
Andreassi in fact found statistically significant differences between the groups. Staff in cardiac catheter laboratories suffered 2.6 times more frequently from skin lesions. Their cataract risk was even higher by a factor of 6.3. Whether cancers occur more frequently – the researcher offers a factor of 3.0 here – remains in actuality an open question. The difference in this case was not statistically significant. An argument presented by Andreassi is that a dose-effect relationship exists. Orthopaedic problems (30.2 percent versus 5.4 percent in the control group) or psychosomatic problems (12.9 versus 2.1 per cent) cannot necessarily be attributed to X-ray sources, but perhaps to mental stress and physical stress. The exposure of extremities to high radiation doses, when not covered by radiation protection, was shown by scientists years ago in the project CONRAD (coordinated network for radiation dosimetry).
The recently published study has two major weaknesses: Maria Grazia Andreassi presented no readings for radiation exposure. She had to settle for estimates. In addition, only 30 percent of all those health professionals contacted sent their questionnaire back – a potential bias on account of the inclusion of participants with diseases. Comparisons with other industries show that her findings are not just something to be dismissed out of hand.
Irradiated for a lifetime
The “International Nuclear Workers Study” (Inworks) is considered to be relatively high quality work due to its broad database. Details of 308 297 employees from nuclear power plants were made available to researchers. The follow-up took in 8.2 million person-years. From among 66,632 death cases 17,957 were traced back to solid tumours. In his publication David B. Richardson from Chapel Hill used an absorbed energy dose in milligray (mGy) on the basis of measured values. On average, the body load for all workers was 20.9 mGy. From this the result is an increase in tumour-related mortality of 48 per cent per Gray. In purely theoretically terms, Richardson traces every 100th cancer death in the cohort back to ionising radiation. Distortions can of course not be excluded when using such retrospectively collected data. However, the Japanese Life Span Study involving survivors of both atomic bombs came to similar results. In addition, Richardson found clear relationships between dose and effect. A threshold dose below which there was no increased risk of cancer did not exist.
Blood in emergency
That low radiation doses do have consequences is something shown by another study already published in mid-2015. Klervi Leuraud from France’s Fontenay-aux-Roses also worked with the INWORKS cohort, but set his focus on disorders of the haematopoietic system. A total number of 1,776 nuclear plant workers died from leukaemias, lymphomas or multiple myelomas. As Leuraud discovered, the association with leukaemias, apart from chronic lymphocytic leukemia, was statistically significant. Per Gray the risk increased by a factor of 2.90. Again, there was a clear dose-response relationship here, but no minimum threshold.
Patient healthy, doctor unwell?
The studies clearly demonstrate that radiation exposure events in the professional environment do not remain free of consequences. What does this mean for physicians and their associated professional assistants? In order to protect patients, the trend is clearly towards a dose reduction. Conventional CT scans are increasingly being replaced by low-dose applications or sonographies. These are also of benefit to doctors. So long as ionising radiation is required for diagnosis or therapy, the question arises as to whether currently valid safeguards are actually sufficient.