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Radiation Safety

Dr Chris Wells, Liverpool, UK

In the early days following the discovery of X-rays, the danger of this medium was not realised. It rapidly became apparent that the invisible rays could cause not only skin cancer but also leukaemia.

Radiologists, technicians and scientists involved in work with X-rays and radium developed many different forms of malignant disease and suffered from an appalling reduction in life expectancy as a result.

Shielding of radiation sources and other techniques reduced the exposure, rapidly reducing the risk. Techniques have been refined over the years so that today Radiologists tend to live longer than their matched medical colleagues. Some cynical colleagues have suggested that this is because of a lack of stress experienced by Radiologists, but I am sure that this is not the case!

Shielding methods in the Radiology Department are first-rate, but some of these techniques are not always applied to fluoroscopy. Many papers on fluoroscopy have appeared in the last decade, indicating assessment of personnel and ways in which this can be minimised, and these include Angiographers, Cardiologists, General Surgeons and Orthopaedic Surgeons. However, very little has been done in measuring the exposure of Pain Clinicians in the Operating Theatre.

Many methods exist to reduce the radiation risk during the use of fluoroscopy. This includes time of exposure, last image hold, pulsed fluoroscopy, reduction of primary and secondary backscatter, primary beam exposure, proper collimation and shielding techniques.

Shielding

All Pain specialists know that shielding is important, but there are 2 problems. One is that the shields can get in the way of the X-ray machine and stop its manoeuvrability. Also they can get in the way of the Operator. The second is that the various pieces of equipment which the Operator wears are uncomfortable and inhibit his ability to operate.

Types of Shielding

1) Lead gown

2) Thyroid shield

3) Eye shield

4) Gloves

5) Patient shield

6) Table shield

The "cathode" or the "gun" of a C-arm projects electrons as an invisible beam of light. These electrons pass through the patient and go on to strike the anode (X-ray plate) at a distance away. The beam widens as it comes out of the cathode, but should be mainly directed towards the anode. If there were no patient in the way, most of these electrons would be captured by the anode. However, on hitting the patient there is a scatter in many directions, some passing directly through to the anode, but with some actually reflected off the patient or the treatment table to produce sidescatter or backscatter. This is the major source of exposure to the Operator and other personnel. The primary beam, the aperture size and the time of exposure have a directly proportional effect on exposure to the patient and consequently to the physician.

Distance from the electron source. Most Operators are aware that dosage falls off according to the inverse square of the distance from the source. As the cathode is not (or should not be) pointing directly at the Operator, the nearness to the cathode is actually not particularly relevant. The proximity of the Operator to the bottom of the table, and the patient, is more pertinent.

Maximal permissible dose equivalent (MPDE): Guidelines have been published, but it should be stressed that these are not SAFETY LIMITS. The best possible dose of radiation is no dose. However, in order for us to do our job we are bound to experience exposure to a certain degree. The principle of ALARA should be applied - As Low As Reasonably Achievable. Guidelines for occupation exposure for Pain specialists and others are one-tenth the limit for occasionally exposed individuals (eg, staff in Theatre) and one-thirtieth times the limit for the general population.

Problems in Practice

Anyone working with radiation needs a film badge. Most people remember to wear this regularly, some don't. It needs to be worn outside of the gown. If you don't wear it it won't work and everyone will think you are safe when you are not. If you do more than one operating list in different sites, you need to have your own film badge and keep it on you at all times.

Over the last 6 months I have been monitoring my exposure to radiation in the 5 Operating Theatres in which I work. Film badges have been worn at 6 sites:-

1) The eye

2) The thyroid

3) The humerus (outside the gown)

4) The ilium (under the gown)

5) The finger (under the glove)

6) The outer aspect of the knee

Measurements are taken over a continual 2 week period using my normal precautions and then a further 2 week period using additional precautions.

Additional precautions are as follows:-

1) Lead glasses (lead lenses plus lead side-pieces)

2) Thyroid shield

3) Superior lead gown

4) Special gloves

5) Side shield between side of patient, bottom of table and cathode

6) (Patient shield)

Initial results indicated a significant level of thyroid exposure, and a very slight but significant level of eye exposure. The lens of the eye can receive a maximum lifetime dose of only 6 REM before cataract formation is likely to occur. I therefore recommend the use of lead glasses. At the moment these are heavy and not particularly comfortable, but hopefully design will improve. As there is no lower dose threshold for thyroid gland exposure, the less the thyroid is exposed, the better. Therefore a thyroid shield is essential.

Gloves, however well made, are expensive and reduce manual dexterity. There was no significant level of exposure to my hands so gloves did not create any noticable effect. Of course if one is going to put one's hands underneath the machine then one is going to get a significant beam. Understandably, for certain procedures this may be essential at times and so gloves can be considered for this type of procedure.

The side shield significantly reduces the exposure to the lower legs. Again, exposure before was at a pretty low level and not one that would worry the Safety Officer, but personally I feel better getting less exposure. As a final note, please remember not to turn your back on the machine whilst looking at the video monitor, if you are wearing one of the new and superior gowns. Not only will you get a decent level of exposure from the machine but your film badge will not be able to measure this because the amount penetrating to the front of your body will be less than 1 per cent.

In the UK you have to attend radiation protection lectures. Most people regard these as a chore and don't listen, often because the topic is presented in a very boring way. However, your eyes, your thyroid and your cancer status should be important to you and it is unlikely that a Health Authority will compensate you if you don't look after it yourself. Insist on a side screen, insist on a thyroid shield and insist on lead glasses. Think about having some gloves available for occasional use. Don't even contemplate wearing 2 pairs of gloves, unless you want to be sued for incompetent procedures!

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