Overexposure of a service technician repairing a biplane X-ray system

Print View Posted on: 19 December 2016

Event Date: 15 July 2014 Event Type: Irradiation/Accelerator Facility
Event Location: Switzerland, Hospital INES Rating: 2 (Final)

While repairing a biplane cardiovascular X-ray system in a hospital, a service technician accidentally activated the system’s floor pedal. Moving a mobile lead shield, he did not realize that the shield was jamming the pedal. He continued his work under unnoticed exposure for about 5 minutes until the system alarm was automatically activated. Most of the time, the upper part of his body was very close to the lateral X-ray tube. He wore a lead apron during the exposure but he forgot to wear his dosimeter that day.

About two hours after the exposure, the technician developed an erythema on parts of his face and neck. The next day, he reported his accident to the competent authorities and was immediately hospitalized in a unit specialized in treating heavily irradiated patients. Frequent blood analysis did not show any sings for an exposure to radiation. After three days, the erythema had vanished and he could leave the hospital. He was treated on outpatient basis. Considering the erythematous reaction and first information available, the local skin dose was roughly estimated to be around 5 Gray.

Three different laboratories were commissioned to estimate the dose by chromosome aberration analysis. All three laboratories reported that the effective dose could not have been higher than 100 mGy.

The Federal Office of Public Health then conducted extensive dose estimations, based on information from the X-ray system's log file and a reconstruction of the incident with a TLD-equiped Alderson phantom. It could be shown that the dismounted collimator was always in front of the lateral X-ray tube, shielding the technician from the direct beam. The dose estimations came to the following conservative results: an effective dose of 5 mSv, a skin dose of 200 mSv, an eye lens dose of 100 mSv and an extremity dose (arm) of 700 mSv.

According to the literature, these doses are way too low to induce an erythema. The cause of the erythema thus remains unclear.

Several security measures were ignored during the repair. The main power was not switched off, the dosimeter was not worn and the warning light was not visible from the technician's position. Corrective actions were demanded from the technician's employer and the hospital as the owner of the x-ray system.

INES Rating: 2 - Incident (Final) as per 19 December 2016
Release beyond authorized limits? No
Overexposure of a member of the public? No
Overexposure of a worker? Yes

Contamination spread within the facility? No
Damage to radiological barriers (incl. fuel damage) within the facility? No

Degradation of Defence In-Depth Yes

Person injured physically or casualty? No
Is there a continuing problem? No

Raphael Elmiger
Federal Office of Public Health - FOPH

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