Preventing accidental exposure in external beam radiotherapy

Frequently asked questions by the health professionals

» How do I minimize the risk of accidents in my clinic? 
» Is there value in learning from accidents in EBRT that have happened elsewhere? 
» As long as there are no overexposure symptoms in my clinic’s patients, are we OK?  
» Major accidents are very rare. How should I approach the more common smaller incidents? 
» What should I do when the cobalt source sticks in the 'beam on' position?

» How do I minimize the risk of accidents  in my clinic?

A good start is to learn from past accidents.

Lessons learned from many accidents point to some general conclusions. Accidental exposures occur when there is an insufficiency in:

• Attention to detail, alertness or awareness. This could also be made worse if personnel have to work in conditions prone to distraction;
• Procedures and checks, or when they are not comprehensive, documented or fully implemented; 
• Qualified and well-trained staff, with necessary educational background and specialized training; 
• Coordination, e.g. gaps and ambiguities in functions of personnel and lines of authority and responsibility. Safety critical tasks can be insufficiently covered. 

Counteracting these conditions will lead you a long way towards minimizing the risk of accidents in your clinic. Help in finding the solutions can be found in some key documents.

Read more:

• INTERNATIONAL ATOMIC ENERGY AGENCY, Lessons Learned from Accidental Exposures in Radiotherapy, IAEA Safety Reports Series No. 17, IAEA, Vienna (2000). 
• INTERNATIONAL COMMISSION ON RADIOLOGICAL PROTECTION, Prevention of Accidental Exposures to Patients Undergoing Radiation Therapy, Publication 86, Pergamon Press, Oxford and New York (2000). 

» Is there value in learning from accidents in EBRT that have happened elsewhere?

Yes, and resources are freely available.

A good way to become informed of why and how accidents might happen is to read the freely downloadable IAEA reports on investigations from accidental exposures. Even if, in these cases, the equipment, the staffing and procedural set-up is different in your clinic, there can be valuable lessons to learn. This is especially the case, when one is prepared to keep an open mind and is ready to see beyond the details of the specifically presented accident.

In addition to these reports, sometimes accounts of accidents are published in scientific journals or disseminated through other means. By sharing this information with others, clinics help to make radiotherapy safer.

Read more:

• INTERNATIONAL ATOMIC ENERGY AGENCY, Accidental overexposure of radiotherapy patients in San José, Costa Rica, STI/PUB/1180, IAEA, Vienna,(1998). 
• INTERNATIONAL ATOMIC ENERGY AGENCY, Investigation of an accidental exposure of radiotherapy patients in Panama, STI/PUB/1114, IAEA, Vienna (2001). 
• INTERNATIONAL ATOMIC ENERGY AGENCY, Accidental overexposure of radiotherapy patients in Białystok, STI/PUB/1027, IAEA, Vienna (2004). 

» As long as there are no overexposure symptoms in my clinic’s patients, are we OK?

Lack of symptoms is, unfortunately, no guarantee that all patients are treated as intended.

Unfortunately acute symptoms of overexposure might only be showing when it is too late to do something to correct the treatment. It should also be kept in mind that situations of underexposure might only be seen in terms of lower-than-expected cure rates of patient groups after many years. In this type of situation, a vast number of patients might be affected by an accidental underexposure before it is discovered.

Read more:

• ASH, D., BATES, T., Report on the clinical effects of inadvertent radiation underdosage in 1045 patients, Clin. Oncol. 6 (1994) 214-225. 

» Major accidents are very rare. How should I approach the more common smaller incidents?

Incidents in radiotherapy should be monitored and approached as important events.

When considering the risks associated with radiotherapy, it should always be taken into account that the patient also has potential benefit from the radiotherapy. The combination of the probability of harm occurring and the consequence of that harm constitute the risk the patient is subjected to from a particular hazard in dose administration.

While the consequence of an incident might be small for the individual patient, the probability of incidents occurring is much greater than the probability of major accidental exposures. Therefore, incidents can still pose a substantial risk in the radiotherapy clinic. One should keep in mind the high level of accuracy for the individual patient required for good practice in radiotherapy.

Another reason for the importance of learning from incidents is that many incidents can have a variable magnitude (e.g. for Patient 1, the mistake causes a dose deviation of 5%, while for Patient 2, the same type of mistake causes a dose deviation of 50%). One should also learn from the potential incidents, or 'near misses'. These are usually even more numerous than the actual incidents, and might correspondingly enable the clinic to find safety critical steps in the treatment chain, and strengthen the defence where it is needed.

Not only should one therefore search for, correct, monitor and learn from incidents in the own clinic, but when an opportunity is given one should learn from incidents in other clinics too. This can be done through a voluntary anonymous incident reporting system shared with other clinics (e.g. Radiation Oncology Safety Information System: ROSIS).

Read more:

• ROSEIS (Radiation Oncology Safety Education and Information system)

» What should I do when the cobalt source sticks in the 'beam on' position?

You should follow the procedure that you have set up before the event happened.

All clinics using cobalt treatment units should have a procedure for this situation. This procedure should be written, clearly displayed, available to and known by all relevant staff, and regular practice sessions should be held. While it is the local clinical responsibility to devise a procedure that is relevant for the local circumstances, there are some general elements to consider when action is taken in the event of a cobalt source not returning to its safe position at the end of treatment.

It is important to note that the points below might not be in the order carried out in your clinic, and they might not cover all aspects according to your clinic's local rules.

• Remain calm;
• Try to stop the irradiation using emergency key/button;
• On some cobalt units, there is a facility to emergency-close collimators to a minimal field;
• Rotate gantry/table so patient is removed from the primary beam;
• Remove the patient from the primary beam; 
• Remove patient safely and quickly from the room;
• If two persons are working on the unit, one person might remain outside and make a note of the time taken for the sequence of steps (for assessment of dose to patient and staff). A stopwatch should be present at the treatment console; 
• Persons entering room should carry dosimeter;
• If the source does not return, it might be necessary to push it back to a safe position using an emergency rod; 
• The person responsible for radiation safety should be contacted, the room door closed and a warning sign hung on door. 

When considering the great importance of getting the patient out of the primary beam, it should be remembered that the dose received by staff is relatively low under normal circumstances when they are avoiding the primary beam. Make sure that all emergency equipment is available at the unit; that the periodic checks are performed (e.g. every morning); and that the unit functions well before taking it back into clinical use after source stick.

Read more:

• INTERNATIONAL COMMISSION ON RADIATION UNITS AND MEASUREMENTS, Prescribing, Recording and Reporting Photon Beam Therapy (Supplement to ICRU Report No. 50), ICRU Report No. 62, ICRU, Bethesda, MD (1999). 
• INTERNATIONAL COMMISSION ON RADIATION UNITS AND MEASUREMENTS, Prescribing, Recording and Reporting Photon Beam Therapy, ICRU Report No. 50, ICRU, Bethesda, MD (1993). 
• McKENZIE, A., et al (Eds), Geometric Uncertainties in Radiotherapy - Defining the Planning Target Volume, British Institute of Radiology, London (2003). 
• INTERNATIONAL ATOMIC ENERGY AGENCY, Radiation Oncology Physics: A Handbook for Teachers and Students, STI/PUB/1196, IAEA, Vienna (2005).