Radiation safety for orthopaedic surgeons - DNB Orthopaedics MS Orthopedics MRCS Exam GUIDE - Orthodnb.com

DNB Orthopaedics  MS Orthopedics  MRCS Exam GUIDE - Orthodnb.com

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Tuesday 4 July 2017

Radiation safety for orthopaedic surgeons

Radiation safety for orthopaedic surgeons
My previous post was on radiation safety for patients, as they are unaware of the adverse effects of radiation and it's our duty to educate and protect them. However, many members were expectedly more interested in surgeon safety and precautions. Hence this sequel.
Orthopaedicians are not excessively exposed to radiation, as orthopaedic surgeries usually don't employ fluoroscopy (like interventional radiologists and cardiologists) and don't need constant image guidance. Most studies have too demonstrated radiation safety of most orthopaedic surgeries (except CT-guided biopsy and kypho-/vertebroplasties, which should better be left for interventional radiologists). Hence, many orthopods have a lackadaisical attitude towards radiation safety and precautions, which is not justified. It's important to know the radiation hazards and sensitise the whole operative team to the required precautions to minimise them.
Ionizing radiations produce a wide array of adverse effects on humans, which may be dose-dependent eg. skin burns, alopecia, cataracts, infertility etc or stochastic (no threshold radiation dose below which these can be totally prevented) eg. cancers. Though one cannot entirely prevent the stochastic effects, but decrease the risk of their occurrence by decreasing the exposure. It should be remembered that the effects of radiation are cumulative and despite a low annual dose of radiation, the cumulative dose over the lifespan of an orthopaedic surgeon can be substantive, whose effects are not entirely known!
The principle of ALARA (as low as reasonably achievable) is the guiding principle, wherever ionizing radiation is used in industrial or medical applications. Radiation exposure can be minimized 
in orthopaedic surgeries by the following measures :-

A. Minimizing use
With an experienced surgeon and C-arm technician, the number of C-arm shots can be brought down to under 100 for most procedures. Unnecessary struggle should be avoided on table and open reduction should be resorted after 3-4 attempts of close reduction. A functional, rather than an anatomical, reduction should be aimed at. Small wedge fragments should not be unnecessarily chased. Only one distal lock can be done in stable fractures. Jig-based distal locking/short nails should be used, wherever possible. Simple fractures in upper limb can be compression plated (instead of MIPO/bridge plating) with excellent results. Each pin and screw should not be inserted under C arm, trusting the tactile feedback and depth gauge. A single check X ray at end suffices for most open reductions.
The 'radiation behaviour' gets established early, during the training of an orthopaedic surgeon and they should be adequately educated and supervised to prevent developing abusive behaviour. Some disincentive linked to the number of images may help curtail such behavior, though it is a matter of further studies.
Busy surgeons should add fellows/senior residents to their team and relegate simple procedures (esp nailings) to them.
B. Increasing distance
Distance is the most important factor affecting radiation scatter (from patient) and absorption (by surgeon).

The further the patient is to the X-ray tube, lesser will be the radiation scatter. Also, keeping the tube too close decreases image field and sharpness. A large field of image is desirable in certain circumstances, such as to study fracture reduction and alignment, otherwise the field should be narrowed with beam collimation. In general, the source should be kept as far from the patient and the image intensifier as close to the patient as possible.
The surgical team should obviously maintain an adequate distance from the C arm, whenever possible. But how much distance is adequate? 99.9% less radiation dose is received, if the surgeon maintains a distance of 18 inches from the X ray beam. Any body part must not fall in the field of direct beam + 18", though certain procedures like manual fracture reduction and K wire passage require the surgeon (or his hands) to enter this zone. With experience, K-wires across long bones can be passed without C-arm, confirming the placement afterwards. However, when put across physes, multiple passes must be avoided and C-arm guidance should be resorted.
Most radiation exposure in orthopaedic procedures occurs from 'back scatter'- the radiation reflected back after striking the patient's body. This occurs upto a 2 meter (~6.5 feet) zone on the side of X-ray tube which should be avoided. The larger the body part, greater is the back-scatter (significant in hip, pelvic and spine imaging).
A surgeon who can maintain these distances (1.5' from beam, 6.5' from X ray tube), like a supervising consultant, doesn't need any protection! Some sources recommend that atleast thyroid shields should be worn even when outside this zone, but I have not read the rationale for such recommendation yet and would not endorse it.
C. Beam direction
This is the next most important point, frequently overlooked by surgeons.
The back scatter occurs off the patient on the side of X-ray tube, and it's important that the X-ray tube is set away from the surgeon.
For the uninitiated, the C arm limb with the round part is the image intensifier (camera), while the other limb (usually bulkier in most models) is the X ray tube.
Hence, PA (instead of AP) images should be taken to keep the X ray scatter towards floor rather than face (Fig 2). Most imaging is done in this plane and all C-arms must be rotated to keep the tubes down. For lateral images, the beam direction should be from medial side, the surgeon standing on the lateral side. At times, space constraints/tube configuration may not allow this, but the proper direction must be followed for AP imaging atleast. The image intensifier should never be used as a table, as it involves lot of back-scatter.
Correct direction of beam can reduce the back scatter and radiation exposure to a huge extent. This is particularly important in pelvic and spine regions, as mentioned above. Spine surgeons continually use AP imaging for pedicle screw insertion and may receive a lot of scattered radiation if the beam direction is reverse.
D. Judicious operation
The radiation dose produced by the machine is defined in terms of voltage (kVp) and current (mAmp). These may need to be adjusted according to the soft tissue thickness, to improve the image quality. Usually increase in one should be compensated by decrease in other to keep the radiation dose in control, and both should not be increased simultaneously.
Most C-arms have ABC (automatic brightness control) to control these 2 automatically as per image quality. The machine should be used in ABC mode only, as much as possible.
Laser grids, if available, help the technician to focus the image well and bring down the radiological wastage. Similarly, collimators narrow down the field of radiation, reducing back-scatter.
Digital zooming (for distal locking), if available in monitor, should be preferred over zooming the image in C arm which increases radiation exposure enormously.
Fluoroscopy (continuous imaging) should be avoided, and pulse, rather than continuous, mode should be used, with a low pulse rate, if such settings are available in machine. Pulse mode decreases radiation by upto 70%. The continuous mode should rather be blocked on the machine, if used exclusively for orthopaedics.
If the theatre complex has a mini C arm too, it should be chosen for smaller anatomic regions (like hand and foot) as it involves less radiation.
E. Shielding/ Personal protective equipment (PPE)
1. Lead aprons
Lead aprons are the most important PPE protecting the internal organs of thorax, abdomen and pelvis. As per some studies, 0.25/0.5 mm lead aprons attenuate the radiation dose by 90%/99% respectively. The latter are the minimum thickness recommended, but if found uncomfortable, lighter aprons should be used instead of avoiding them altogether (most aprons in our country are 0.25 mm). Wraparound aprons (top right in figure 1) are recommended for circumferential protection, rather than the regular front apron (top left, Fig 1). However, these become even heavier and almost impossible to wear. Two piece aprons (skirt-top) distribute the weight between shoulders and pelvis and are more comfortable, though not widely available.
The annual permissible radiation dose to chest/gonads is 20 mSv, which may be reached if one is doing 3-4 heavily image guided surgeries per day, despite wearing lead aprons. On the other hand, if one is doing only 1-2 image-guided surgeries per week, this limit may not be reached even without lead aprons.
2. Thyroid shields
The permissible annual radiation dose for thyroid is 150 mSv/year (7.5 times the body dose), which is not reached even if 3-4 heavily image-guided surgeries are done per day without thyroid shield.
However, the thyroid guard attenuates the radiation by 2.5 to 3 times and should be worn electively to avoid cumulative and stochastic effects.
3. Lead gloves
The permissible annual radiation dose for hands is 500 mSv, which cannot be reached in orthopaedic surgeries. Moreover, lead gloves have not been demonstrated to impart substantial protection when hands are directly in field.
Lead gloves are thus not warranted for orthopaedicians.
4. Lead glasses
Even lead impregnated glasses (bottom right in Fig 1) are available to protect the eyes from cataract, though such high dose can again not be reached in orthopaedic procedures. Cataracts have not been known to occur in orthopods due to radiation, as in interventional radiologists and cardiologists.
F. Monitoring/ maintenance
1. C arm
The use of C-arm during the surgery should be monitored. Most models have an alarm system which can set to beep after a set number of shots (say every 100) or after a specified duration of imaging (say every minute). This warns the surgeon of excessive usage.
C-arm loses efficiency over time and periodic inspection/ service helps maintain it well. Timely replacement of the machine/tube every 5-10 years should be done, depending upon workload.
2. Lead aprons
Lead aprons crack easily and should not be folded. They should be hung straight on dedicated stands in OT complex. Periodically, once in 6 or 12 months, these should be X-rayed to ensure the extent of attenuation and pick up any damage.
3. Dosimeters
TLD (Thermoluminescent dosimeters) badges are available from BARC and should be worn to keep a track of one's radiation exposure. It's recommended to wear multiple badges, as over neck, chest, gonads and hands. However, a single badge at waist level suffices for us. These should be ideally stored in lead boxes after use to protect from terrestrial radiation.
Such badges can caution one against excess exposure and help take remedial action.

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