Contamination of an employee and a staff break room in a nuclear medicine department, with reclassification on the INES scale

Scintigraphy is an imaging technique that consists in administering a radiopharmaceutical drug to a patient, which then diffuses into the organism or the organs to be examined. A detector, called a gamma camera, coupled with a computerised image acquisition and analysis system, then produces images of the functioning of the explored tissues or organs.

On 21 July 2022, the radiographer in charge of preparing the radiopharmaceutical drug syringes was in the break room when the alarm of the active dosimeter worn under his lead apron was activated. The subsequent verification confirmed contamination of the skin of one of the person's forearms. The radiographer immediately underwent the decontamination procedure prescribed for this type of situation.

The centre's radiation protection advisor then carried out radiation checks in the rooms and on the equipment; they revealed a low level of contamination in the preparation chamber and on the edge of the table in the break room. The chamber and table underwent surface decontamination, but the table edge could not be entirely decontaminated therefore the break room was closed and the still-contaminated area was cordoned off until the radioactive elements had decayed. Given their short half-life, these radioactive elements disappear naturally in a few days.

The event resulted more specifically from noncompliance with several internal procedures,

• including: utilisation of the shielded radiopharmaceutical preparation chamber without prior installation of the gloves that seal the chamber
•     failure to check for contamination on leaving the contamination-risk zone, which delayed detection of the contamination;
• and sub-optimal allocation of the radiographers' tasks during the vacation period.

The initial dosimetric results transmitted seemed to indicate that the dosimetric consequences of this event for the worker would be limited, as the received doses in principle remained below the maximum values set by the regulations. Based on these factors, ASN provisionally rated this event level 1 on the INES scale and published an incident notice on 12 August 2022.

The analysis of the radiotoxicological examinations of the radiographer's urine revealed internal contamination within the statutory limits. However, based on complementary analyses conducted by IRSN, the French Institute of Radiation Protection and Nuclear Safety, the equivalent dose to the skin received by the worker was estimated at more than 4 times the statutory limit of 500 mSv over twelve consecutive months.

Given that the statutory occupational exposure limit for the skin was exceeded in a single event, ASN uprated  this event to level 2 on the INES scale (International Nuclear Event Scale, rated from 0 to 7 in increasing order of severity).

The centre sent ASN a significant event report with proposed corrective actions. These actions were analysed then discussed during an on-site ASN inspection on 6 April 2023. They raised no remarks from ASN. The centre was nevertheless informed that it must verify the medium- and long-term effectiveness of the corrective action.