Quarterly assessment of radiotherapy events, classified as level 1 on the ASN-SFRO scale, reported between 1 July and 31 December 2010

Seventy-nine significant radiation protection events, including four in brachytherapy, classified as level 1 on the ASN-SFRO scale, were reported between 1 July and 31 December 2010.

Each event reported concerned only one patient.

Although these events are not expected to have any impact on patients' health, they are analysed to see if any lessons can be learnt from them (particularly in terms of organisation) and to avoid any recurrence.

Most of the events reported – 55 out of 79 – related to patient positioning errors or target volume errors resulting in the exposure of areas not intended for treatment.

Three of the four brachytherapy events reported involved incorrect positioning of radioactive sources in the target volume or cases where the source moved outside this volume.

Twelve events were due to mistaken patient identity caused by human error, some of which were combined with technical or organisational failures.

Ten events concerned dose errors caused by either one or more unscheduled extra doses being administered after treatment, or by a fractioning error or a mistake in noting down the prescribed dose. One brachytherapy event was due to a mistake in calculating source activity.

Lastly, one event was caused by a beam forming error connected with poor collimator design.

ASN investigates level-1 events during specific inspections and during its regular inspections of radiotherapy centres. After a centre has analysed an event, ASN systematically examines all the corrective measures proposed.

ASN observes that events caused by incorrect positioning of the patient remain the most common: these events are most often due to failure to correctly locate the reference point used for identifying the target volume, treatment of the wrong side, failure to take into account offsets provided for when preparing the treatment, or confusion of the different reference points used for successive treatment phases.