Unintended and accidental medical radiation exposures in radiology: guidelines on investigation and prevention

If an incident is caused by an error made by staff in the department or practice using the x-rays (table 1, nos. 1a, 2, 3, and 4), the person carrying out the investigation should take all necessary measures to obtain detailed information, which in many cases will include face-to-face interviews with the staff involved, to determine causes of the incidents and identify contributory factors. They will need to consult a medical physics expert to obtain radiation dose information. The investigation should be instituted with an open 'no blame' approach and aim to identify root causes and contributory factors. Details of what occurred, why it happened, and any deficiencies in procedures or staff training that contributed to the incident should be included in the report. Follow-up should look at remedial actions, to see what improvements should or could be made to minimize the risk of a similar incident occurring in the future. On completion of the investigation, a debrief of all staff involved should be carried out to explain causes of the incident, and describe any adjustments that have been made to procedures and other changes.

There may be latent systemic factors within the department, such as too many distractions within the workplace or staff shortages that contribute to active errors categories 1a, 2, and 4; also known as human errors. Examples of such latent factors are listed in table 2. Active factors may be due to decisions linked to poor staff alertness and awareness. The responsibility for addressing the deficiencies will lie with the manager or lead person for the service, and the requirement to ensure that any changes necessary are implemented to address deficiencies in procedures and training should be included in the procedures. However, all relevant stakeholders should collaborate in the process. There may be modifications to procedures, additional training of staff, introduction of additional checks, or other changes. There may also be adjustments to the organization of the service, to improve clarity for responsibilities.

Steps that should be taken following an incident have been described, but the objective is to avoid the occurrence of such incidents in the first place. A variety of systems can be adopted to help in achieving this and some examples are given in table 3. Professional organizations such as Image Gently (www.imagegently.org) for children and Image Wisely (www.imagewisely.org) for adults promote the use of tools to help in this process, such as checklists and audits to assist in the improvement process. In order to prevent incidents there should be a continuing effort to refine procedures. Before starting a procedure, it is useful to pause for a moment while everyone confirms that the actions highlighted in the checklist have been performed or are in place. This type of 'pause and check' routine has been promoted by professional organizations in radiology (Image Gently 2014, The Society of Radiographers 2017). The checks for paediatric fluoroscopy, for example, include: the correct patient, the possibility of pregnancy, justification of the examination, the anatomical site, radiation safety aspects, optimization of the procedure, and use of AEC and grid. If these factors are written down on a card or poster, and the checks followed at the start of every procedure, this can help to avoid obvious errors.

Incidents can sometimes result from a lack of clarity about individual responsibilities for carrying out particular tasks. An example of a situation where there may be some dubiety about responsibilities is when x-ray equipment is being maintained by a company x-ray engineer. Here the use of a formal equipment handover procedure, with appropriate checklists, can help to ensure that the responsibility for the equipment and its correct operation is recognized. Then, if access to the room and equipment is required for an emergency clinical procedure, all the checks should be made to ensure the equipment is set-up appropriately for clinical use, according to the predetermined format. Such strategies linked with periodic review and audit of procedures, and proper follow-up of any incidents that do occur, should enable robust procedures to be developed that will avoid most incidents.

There are many reports of tissue reactions resulting from interventional procedures in cardiac catheterization laboratories and interventional radiology suites (Rosenthal et al 1997, Vañó et al 1998, ICRP 2000a, 2013a, Koenig et al 2001a, Koenig et al 2001b, Vliestra et al 2004, Bogeart et al 2009, Balter et al 2010, UNSCEAR 2010, IAEA 2010, Vañó et al 2013). When effects occur or when dose levels are such as to give a high risk of them occurring, a review of procedures may be appropriate, as required for other incidents. However, doses are not measured and even dose estimates are unfamiliar so in many institutions and radiology practices staff members are unaware of dose levels and whether there might be a clinically significant risk. When dosimetry information is not available, there is no indication of the potential for tissue reactions, and the link between cases of erythema and radiation exposure may not be recognized. Even when dose information is displayed, the quantities may not be familiar to or understood by the operators, so education in dosimetry and the link to radiation effects is important. If the threshold dose to cause injury is exceeded, the tissue damage will become progressively more severe with increasing dose, but the extent of a tissue reaction injury may not become apparent until weeks or months later. As a result, any association between reported erythema and a radiation exposure may be harder to establish, particularly if the possibility is not mentioned at the time an interventional procedure is carried out. Moreover, staff may not believe that radiation injuries could have resulted from the interventional procedures carried out, if they have not previously been alerted to the possibility. Some cases requiring skin grafting have only been recognized almost a year after exposures occurred (Rehani and Srimahachota 2011, Kostova-Lefterova et al 2017, IAEA 2017a). Since there is a risk of skin injury from interventional procedures, patient consent must be obtained and the radiation risks including clinical manifestations of radiation injury associated with the procedure discussed with the patient if the expected skin dose may be high.

The potentially high radiation levels from interventional procedures coupled with the need for the operators to be close to the patient to perform the necessary manipulations mean that there is also a higher risk of occupational exposure. Reports of lens opacities among interventional staff resulting from exposure over many years highlight the importance of optimizing not only the radiation levels used, but also the appropriate use of protective methods and devices for staff (ICRP 2000a, ICRP 2012, IAEA 2017d).

It is important to put in place procedures to prevent or at least minimize the risk of skin injury, through awareness of potential dose levels before and during any interventional procedure (table 3). High skin doses often result from poor technique and lack of optimization and sometimes occur due to equipment malfunction (Rosenthal et al 1997), but others while not intended are difficult to avoid because of the complexity of the procedure (Bryk et al 2006, Suzuki et al 2008, Vano et al 2013). Hospitals should identify procedures that have a high potential to cause radiation injury and ensure that the competencies for operators and the equipment settings used are satisfactory (ICRP 2000a). Approaches to reducing these risks in different parts of the world will need to take into consideration the technology and resources available. There are many factors that can contribute to doses being higher than necessary. If the interventionalist does not have a detailed knowledge of all operation modes of the x-ray unit, he/she may not make full use of the patient dose optimization techniques available. The default settings in terms of radiation dose and image quality may not be appropriate for certain patients and procedures. These settings should be optimized during commissioning of the equipment and operators trained in use of the facilities. Involvement of medical physics experts during the commissioning and when the applications specialist is setting-up program options with the operators will assist in informing decisions on dose and image quality. Ensuring that sufficient training is given to interventionalists and radiographers in techniques to minimize skin doses for interventional procedures, such as keeping the image receptor close to the patient, using the lowest appropriate pulsed fluoroscopic and image acquisition dose rates necessary for each stage of the procedure, rotating the gantry slightly to vary the beam entry point, and collimating the x-ray beam as much as possible are crucial (Mahesh 2001, Miller et al 2002, Stecker et al 2009, ICRP 2013a, NCRP 2011, IAEA 2010, Hill et al 2017). The training must include unique considerations for paediatric procedures as well as the impact of geometrical factors in the operation of C-arm equipment, such as the influence of iso-centre position, and the potential for the x-ray tube being much closer to the skin surface for oblique projections and so delivering higher skin doses, as well as ensuring the patient's arms do not lie within the primary beam, which has led to injuries in the past (Vañó et al 1998, Vliestra et al 2004, ICRP 2013a). Interventionalists must understand the impact of all the dose management features of the equipment and how to use those features properly. Training in techniques and radiation protection for cardiologists, surgeons, and other clinicians using C-arm equipment, in addition to radiologists (ICRP 2009, 2010, 2013b), will help to avoid practices that may give radiation doses that have the potential to cause skin injury. Free training material on radiation protection in image guided interventional procedures, available on the IAEA website, provides comprehensive information (IAEA 2017b), together with posters on radiation protection methodology in many languages (IAEA 2017c). Exposure levels in neuroradiology, especially interventional neuroradiology, can be a particular problem, because fields focussed on the head will often overlap, irradiating the same area of the skull and these can result in hair loss (Mooney et al 2000, Imanishi et al 2005).

The threshold and severity of tissue reaction is linked to peak skin dose and the area of skin irradiated. The skin dose will depend on the complexity of the procedure as well as the size of the patient, so procedures where there is a potential risk of exceeding a peak skin dose of 3 Gy should be identified. Repeated procedures with dose levels over about 1 Gy on the same patient within a few months will also increase the risk of injury. In all these cases there is a need to be aware of high doses from previous procedures and to look for strategies to reduce peak skin doses (ICRP 2000a).

Software for mapping skin dose distributions from interventional procedures is becoming available (Johnson et al 2011, Khodadadegan et al 2013) and some modern interventional systems can provide real-time estimates of peak skin dose and maps of dose distribution calculated from exposure parameters (Bordier et al 2015). As these systems become more accessible they should provide operators with the possibility of monitoring peak skin dose throughout a procedure. Although these options are not available on the majority of interventional fluoroscopy units at the present time, there are dose quantities that can be used as indicators such as cumulative air kerma at the interventional reference point, KAP, fluoroscopy time, and number of image acquisition runs/frames. The accuracy of the dosimetry data displayed should be validated by a medical physicist. Protocols should be available which take into account patient size, and contain alert and trigger levels set in terms of the displayed quantities. The levels should be based on recommendations of professional societies, and the values included in operator training (cardiologist, radiologist, radiographer, and other medical specialists using fluoroscopically guided procedures). Values that might be used based on international guidelines are included in table 4 (Stecker et al 2009). The more appropriate quantity is the cumulative air kerma at the interventional reference point. However, it should be recognized that this is not an accurate measure of skin dose, as it is based on the assumptions that the skin surface is 15 cm in front of the iso-centre and the x-ray tube is stationary. Moreover, it does not include backscatter which can increase skin dose by 30%–40% or attenuation of the x-ray table. It may therefore be higher or lower than the peak skin dose, so ideally calibration and assessment by a medical physics expert is required. Older equipment may not provide dosimetry information and here fluoroscopy time should be used as a guide, although this is a poor indicator of radiation dose.

Radiation dose estimates should be monitored throughout a procedure for all patients, especially those who are considered to be at risk of skin injury, and the responsibility for this may be delegated to a radiographer, medical physicist or nurse. The interventionalist should be alerted during the procedure when the dose reaches the alert values (Stecker et al 2009). The clinical outcome must be the priority, even if an alert level is reached, so clear recommendations should be made about action to be taken. These may include modifying the procedure or consulting a colleague for advice. Higher trigger levels should be set above which the patient would be informed and followed-up, and for external reporting of the exposure. If any of the dose alerts are exceeded during a procedure, the dose information should be recorded in the patient's medical record (Miller et al 2004, NCRP 2014). The patient should also be monitored closely if any further procedures are performed during the next two months, and the dose from the first procedure taken into account. If the dosimetry parameter exceeds the trigger level for follow-up, then the patient should be informed of the risk. A patient information sheet should be issued on discharge recommending that a family member or other caregiver inspect the area of skin irradiated for signs of redness or rash two weeks later and including resources for the patient to contact if any effects are observed (Stecker et al 2009). The high skin dose should be entered into the patient's medical record and the patient's condition followed-up on their return to the hospital or they may be contacted after approximately three weeks to check whether they have had any skin reaction. The patient's general practitioner, referring doctor, and other professionals involved in the service should all be informed of the procedural exposure.

The IAEA has established an international web-based database SAFRAD (Safety in Radiological Procedures) to collect radiation exposure data for procedures reaching defined trigger levels in interventional radiology and cardiology (IAEA 2017e). The purpose is to identify patients at high risk of developing tissue reactions from interventional procedures, encourage follow-up examinations for adverse side effects, and educate healthcare personnel. The IAEA requests that events are reported to SAFRAD if one of the following levels is exceeded: fluoroscopy time > 60 min, KAP > 500 Gy cm², cumulative air kerma at the interventional reference point > 5 Gy, measured peak skin dose > 3 Gy, number of series or cine runs > 20. SAFRAD also defines the following trigger levels for reporting: observed radiation injury, wrong patient, wrong procedure, unknown pregnancy at time of procedure, or multiple procedures within 12 months.

Events that lead to tissue reactions from CT scans are rare, but if they occur can affect multiple patients, as they are likely to result from use of inappropriate exposure settings (New York Times 2010, 2011). Procedures with higher risks of skin injury are CT fluoroscopy and CT perfusion (ICRP 2000b, ICRP 2007b). Dynamic CT perfusion involves a series of continuous or intermittent CT acquisitions from which functional haemodynamic parameters such as blood flow, blood volume, mean transit time, and time to peak enhancement can be derived (Hoeffner et al 2004). Brain CT perfusion is used for assessment of stroke. The technique may be employed for the body primarily in oncology applications for lesion characterization and assessment of tumour response to medication and radiation treatment, and also in evaluating cardiac function (Kambadakone and Sahani 2009). There is a risk of high skin doses in CT fluoroscopy, because scans performed during guidance of a needle, catheter, or probe may be repeated in approximately the same location (Teeuwisse et al 2001, Tsalafoutas et al 2007). Examples of skin injury and hair loss from CT perfusion cases in the USA have been publicized (ICRP 2007b, New York Times 2010, 2011). These have involved errors due to use of incorrect settings by operators who did not understand the potential impact of CT parameter changes on dose. Examples include selecting a 'Noise Index' for controlling the tube current modulation mode that was too low, yielding doses many times higher than necessary; scanning a patient multiple times because of lack of awareness that multiple image reconstructions could be obtained from the same raw data (Mettler 2017); and a missing beam filter that was dislodged during shipping (Mahesh 2017). Lessons that have been learned from these accidental overexposures are to ensure that acceptance testing is carried out, including comparisons of performance with manufacturer specifications, as well as regular quality control, and to act immediately when an event occurs to assess the radiation dose levels; communicate the findings to everyone involved; and modify procedures in an attempt to avoid future incidents (Mayo-Smith et al 2014, FDA 2017). As a result of these incidents, new regulations have been introduced in the State of California requiring accreditation of all CT scanners, annual evaluation by suitably qualified medical physicists, and recording of CT dose descriptors in patient reports for every CT examination (California Law SB 1237). Annual verification of the accuracy of CT dose displays is particularly important.

Methods for prevention of incidents should first identify procedures that have a high potential to cause injury and ensure the settings are satisfactory, but also review of all CT protocols including evaluation of dose especially those for more common examinations. CT skin dose is not measured directly on patients, but the volume averaged CT dose index (CTDI_vol) displayed on the scanner console provides useful information. The CTDI_vol is an average of the dose at the surface and at the centre of a phantom. For head CT scans, the dose is similar throughout the phantom and so the CTDI_vol is similar to the surface skin dose. However, for body CT scans, the CTDI_vol underestimates surface skin dose and the relationship to compute skin dose ∼1.3 × CTDI_vol should be used (Mahesh 2017).

Recently, a 'CT Dose Alert' standard (NEMA 2013) has been introduced, which will provide an alert to CT machine operators if the scan parameters that have been set will give doses that exceed levels predetermined by the users. The purpose of the CT Dose Alert is to avoid excessive dose delivery due to incorrect settings or repeat scans. The US Food and Drug Administration (FDA) has suggested a CT alert value for CTDI_vol of 1 Gy, which should allow the user to adjust the scan settings to avoid any potential skin injuries (FDA 2009, FDA 2010). In addition, the user also has the option to set 'CT Dose Notification' levels (AAPM 2011) for CTDI_vol and DLP that can be chosen for each scan series and when these levels would be exceeded, programs will alert the operator prior to the examination. If the operator wishes to continue with the parameters that have been set, then reasons have to be documented. The CT Dose Notification option can be a useful tool for quality management and users can monitor their respective CT practice by routinely auditing the CT dose reports (Mahesh 2016).