UK Health Security Agency is the UK's primary authority carrying out research to advance knowledge about protection from the risks of radiation. We provide world-leading advice, training and services for the widest range of radiation protection safety professionals, organisations and members of the public.

Case study: CT overexposure

A patient outside the EU experienced two partial body exposures to the head during CT scanning, 21 months prior to blood sampling. Overexposure was suspected and chromosomal analysis requested by the patient's GP.

Chromosomal analysis revealed higher yields of both dicentrics and translocations than expected. Using FISH translocation analysis as the most appropriate given the sampling delay, comparison with an appropriate calibration curve and associated statistical analysis suggested that for two exposures approximately 1 month apart, the doses were in the region of 200 mGy each.

It was concluded that both translocation and dicentric levels were slightly higher than the spontaneous levels observed in non-exposed individuals and were consistent with a low dose whole body exposure of the order of 100-200 mGy X-rays, with large uncertainties.

Case study: Rapid assessment and reassurance

10 industrial workers were suspected of overexposure from an unshielded 169Yb radiography source. Health physics calculations suggested that any exposures would have been below the detection limit for the chromosomal aberration; however, the incident was discovered very promptly and it was possible to take blood samples 8 hours later within the short time window to allow the new gamma-H2AX foci assay to be used. The samples were transported on ice to UKHSA and analysis was carried out and the results returned to the company and the individuals within a few hours, ruling out any high or significant whole body dose. This reassurance was aimed at reducing the stress and anxiety of the exposed individuals before further sampling and analysis using the more accurate, but time consuming, traditional cytogenetic assays.

Case study: Eye problems suspected of being linked to linear accelerator accident

A man developed a series of eye problems commencing 1 week after having been exposed to radiation leaking through a defective door to a linear accelerator, and after 6 weeks a cataract developed. The individual was concerned that this was radiation induced despite the absence of any accompanying facial skin effects and the advice that the time delay was judged to be far too short for radiation induced cataract development. Biological dosimetry was requested to further explore the possibility of radiation exposure: 1000 cells were scored and no chromosomal aberration was detected. The best estimate of his averaged whole body dose was zero, with the calculated uncertainties suggesting a 2.5% chance that an averaged whole body dose of about 100 mGy could have been received with no chromosomal damage detected. If only a small volume of the body had been exposed briefly from a narrow beam through a small aperture in the shielding, it was very unlikely that the damage would have been detected, due to the dilution of the few exposed blood cells into the whole blood pool. However, it was judged that a local dose sufficient to cause clinical concern or a cataract within 6 weeks, which would otherwise have resulted in localised erythema (skin reddening), was unlikely to have been received, hence providing reassurance to the individual.