Quarterly assessment of radiotherapy events, classified as level 1 on the ASN-SFRO scale, reported between 1 April and 30 June 2010

Published on 24/08/2010 • 10:32 am

Information notice

Twenty-one events, classified as level 1 on the ASN-SFRO scale, were reported between 1 April and 30 June 2010. 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 as regards organisation) and to avoid any recurrence.

 Each event reported concerned only one patient.

 Thirteen of the events concerned patient positioning errors as follows:


  •  four errors relating to identification of the reference point used in locating the target area for each treatment session. In two cases, these errors arose from confusion with a mole or with a reference point used for a previous treatment; in one other case, there was confusion between the reference points used in the two phases of the patient’s treatment. The fourth error was due to incorrect marking of the reference point during the preparatory stage of treatment;
  • In the case of treatment involving two target areas, an error resulted in the first area being irradiated with the beams intended for the second area;
  • failure to take into account or correctly apply offsets in relation to the reference point for two patients. These two events occurred at two different centres;
  • the use of incorrect marks made on a repositioning tool;
  • failure to detect error in patient’s position on the control image at the start of treatment. This event occurred with three patients at two different centres;
  • wrong side treated;
  • patient's position reversed (in the head-to-foot direction) during part of a session.


 Four events concerned the administration of an inappropriate dose, due to:

  • one case of mistaken identity concerning a patient receiving treatment for one session;
  • an incorrect dose administered during a session;
  • dose to be administered incorrectly staggered: treatment that was supposed to comprise four sessions per week was given at the rate of five sessions per week for the entire duration of treatment (28 sessions);
  • an unscheduled additional session conducted at the end of treatment.


 Four events concerned a beam shaping error due to:


  • a collimator aiming error (the collimator is the part of the accelerator used to size the treatment beam);
  • incorrect distance between the radiation source and the patient;
  • loss of computer data on the positioning of a collimator;
  • confusion between the lead protection (which can be used to form complex-shaped treatment areas) initially provided for and the modified protection.


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

Corrective measures for the period concerned here included a requirement for some of the centres having reported an event to put measures in place to make the reference point more visible and step up staff training in virtual simulation techniques[1].

Corrective measures also led to modification and improvement of the procedure for checking parameters for treatment plans before they are initiated, applicable for a reporting centre.

With regard to the previous four quarterly assessments, it seems that events caused by incorrect positioning of the patient are 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 or failure to take into account offsets provided for during preparation.

 [1] technique used during preparation for external radiotherapy treatment: at this stage, information about the patient’s anatomy is obtained by means of scanner images, which are then used to define the area to be treated so that the reference point can be marked on the patient’s skin.

Date of last update : 08/06/2017