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

Between 1 April and 30 June 2011, twenty-four significant radiation protection events occurring during radiotherapy were classified as level 1 on the ASN-SFRO scale. The events, which are not expected to have any impact on patients' health, were nevertheless analysed to see if any lessons can be learnt from them (particularly in terms of organisation) and to avoid any recurrence.

Each event reported concerned only one patient.

Most of the events (14 of 24) were due to abnormal positioning of the patient that resulted in exposure of an unintended area related to

• erroneous application of offsets provided with regard to the reference point used to identify the treatment area;
• confusion with previous tattoo points;
• erroneous interpretations of a reference image used to position the patient.

Six events concerned an error in identification of patients due to :

• confusing two patients (patients with same name or a patient taking the place of another);
• treatment protocol (homonymy, unscheduled appointment change in treatment software).

Three events concerned a dosage error related to

• use of incorrect treatment beam energy;
• neglect of a bolus when administering treatment;
• fractionating a treatment dose different from the one prescribed.

Lastly, one event was caused by a beam forming error due to use of an incorrect collimator.

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

The most notable corrective measures for the period under consideration consist of  restating instructions for verifying the identity of the patient and use of photo identification;

• implementing double verification of centring devices and reminding radiographers to read notes about positioning before placing patient on the treatment table;
• acting on the organisational level by
• avoiding changes of team while a patient is being treated;
• focussing the work of radiographers assigned to treatment posts to essential tasks to limit work disruptions;
• optimizing scheduling of patient appointments to improve management of patient flow.