Which type of shielding should be used during an examination that requires a sterile field?

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Lead Aprons

For reasons of weight, lead aprons generally have shielding equivalence equal to a 0.25–0.5-mm lead barrier, and will only attenuate the radiation. Lead aprons absorb 90%–95% of scattered radiation that reaches them (Table 77.5). “Wrap-around” lead aprons are useful when medical personnel spend a lot of time with their backs turned away from the patient. When wrap-around aprons are not used, the personnel wearing them should not turn their unshielded backs toward the x-ray beam. Lead aprons should be worn and stored properly. They should not be folded or thrown on the floor since it may produce creases that develop into breaks in the protective barrier. The integrity of lead aprons should be assessed annually.

Protective Shielding and Personal Equipment

Everyone working in the implant environment should wear a lead apron and a thyroid collar or be positioned behind a mobile lead shield during an implant procedure (Fig. 5.2). Many operators wear leaded glasses to minimize exposure to the eyes. A lead skirt shield should be positioned at the table and can be attached for convenience during the procedure (Fig. 5.3). Lead shields should be tested intermittently to make sure that there are no radiation leaks that develop through flexible x-radiation protection.

Occupational radiation exposure can also be reduced by the use of a bismuth-containing, sterile disposable shield. When positioned just caudal and lateral to the intended device pocket region, these radiation-absorbing shields can decrease absorbed radiation to the operator by up to 80%.8 Widespread use of this device may be hampered by cost considerations.

Recent data suggest that radiation (some from scatter) to the brain (particularly the left side of the brain for right-sided implant procedures and vice versa) may be detrimental. Head caps of flexible barium sulfate and bismuth oxide strips, constructed with lightweight cloth, can attenuate radiation to the brain equivalent to a lead that is 0.5 mm thick.9 Full radiation protection cabins have been shown to reduce exposure to the operator by over 90%, without increasing procedure time or complication rates.10 Despite this finding, they remain costly and somewhat cumbersome, limiting their overall use. Standing behind another individual in closer proximity to the radiation field may offer no protection. Instead, perhaps through scatter and more favorable positioning of protective devices toward the primary operator, radiation exposure may actually be higher for a second operator.11 This has important implications for those in a position of instruction and emphasizes the need for optimal use of shielding protective for both the primary and secondary operators.

Bismuth radiation pads used to reduce x-radiation exposure to a patient’s breasts and eyes for computed tomography scans have been proposed and are controversial but to date have not been used for cardiac implantable electronic device (CIED) implantation.

Careful use of fluoroscopy can reduce the amount needed and not affect the ability to perform the implantation and not adversely affect the safety to the patient. Experienced implanters can routinely implant single- and dual-chamber pacemakers and implantable defibrillators with less than 1 to 2 minutes of fluoroscopy, and in some cases only a few seconds. Table 5.3 provides recommendations for CIED implantation to reduce radiation exposure.

Protective Garments

Lead protective garments are standard required protection to anyone being exposed to radiation. Lead aprons and/or skirt and vest garments need to be between 0.35 and 0.5 mm thick, properly stored, and inspected every 6 months to a year for cracks, creases, or rupture to ensure adequate protection. The garments not only protect the covered organs but also reduce the total body effective dose of exposure as much as 16-fold. The use of a thyroid collar protects the thyroid from the minimal exposure risk and also reduces the total effective dose by a factor between 1.7 and 3. Protective 0.15-mm lead–equivalent glasses or goggles limit the eye lens dose and provide about 70% attenuation even in high energy (kVp) beams. The angle and distance of the beam to the patient will determine the amount of scatter. Increased exposure dose results from oblique or lateral views and higher image intensifier distance from the patient and table. These factors should be considered while acquiring the images. Shields attached to the ceiling and screens that move in and out of the procedure room also provide increased protection from radiation.

An underestimated occupational hazard associated with the use of lead gowns, aprons, and vests is cervical and lumbar spine injuries. The rationale for a skirt and vest in contrast to a full lead apron is to split the weight of the lead between the shoulders and the hips, thus distributing the weight between the upper cervical/thoracic spine and the lumbar spine. Using lighter lead is an obvious approach within the limits of lead thickness and safety requirements. However, in those who have symptoms of cervical disk disease, a single-piece lead gown with a tight belt around the waist is effective in transmitting all the weight to the hips, thus relieving all the weight from the cervical spine. For those who have symptoms, early diagnosis with magnetic resonance imaging and a physical therapy program can frequently reduce symptoms and control the risk of more serious injury.

Radiologic Protection

Protective barriers should be readily available and should be used liberally. The most important of these is the lead apron. Aprons are generally available in 0.5- and 0.25-mm thicknesses. In optimal circumstances, the 0.5-mm thickness has the ability to attenuate 98% to 99.5% of the radiation dose, whereas the 0.25-mm thickness attenuates approximately 96% of the dose.13,17 Deterioration of the apron’s lead lining occurs with use and is increased by rough handling or improper storage. Aprons should undergo periodic screening and replacement if inadequate protection is found, depending on the location of the defect. It has been recommended that aprons should be replaced if there are defects over noncritical areas for which the sum of all defects exceeds 670 mm2, or the equivalent of a 29-mm diameter circular hole. If the defects are over critical areas, such as the gonads or thyroid, aprons should be replaced if the sum of the defects exceeds 11 mm2, or the equivalent of a 3.8-mm diameter circular hole. A thyroid shield with a greater than 11 mm2 defect should be replaced.18 Many aprons are not of the wraparound type and therefore do not provide circumferential protection. Scattered radiation from the sides may produce unprotected exposure.

A thyroid collar and protective glasses are essential. These glasses are highly variable in the amount of protection afforded and allow for a low of 3% to a high of 98% transmission of the radioactive beam.19 The greatest protective effect is obtained with glasses containing lead. Glasses at the lower end of this spectrum may provide protection from ultraviolet rays but not ionizing radiation. Also of note is that a significant amount of the ocular exposure, up to 21%, is the result of scatter from the operator’s head.19 Depending on the head position of the operator during the procedure, side shields or wraparound configurations are necessary to provide adequate protection.

A lead acrylic shield, which can be either ceiling mounted or positioned on a mobile floor stand, should be placed between the operator and the patient to reduce exposure further. Eye radiation can be reduced by a factor of 20 to 35 with the use of a ceiling-suspended lead glass shield.8,12 Lead-lined gloves also help reduce exposure but can be cumbersome. Because (1) backscattered radiation is more intense than forward scattered radiation20 and (2) with the C-arm in the posteroanterior orientation, the greatest exposure due to scatter occurs from under the table, we use a lead drape suspended from the operating table on the operator’s side to reduce exposure. Using this additional shield eliminates a significant amount of this scatter.6

Use Proper Shielding

Only the personnel needed to conduct the procedure should be in the fluoroscopy suite. Everyone should be shielded with lead apronsbefore fluoroscopy begins. The person using the fluoroscopy unit should alert everyone in the room that he or she is about to begin and ensure that all personnel are shielded. Routine use of thyroid shields can minimize the long-term risk of thyroid cancer. Although protective lead gloves can reduce the exposure of the hands to radiation, they can produce a false sense of security. When leaded gloves are used and the person's hands are in the field of exposure, units with ABC will increase their output to compensate for the radiodense leaded gloves, and negate their protective effects. Techniques that prevent the physician's hands from direct exposure within the x-ray field should be used at all times. Protective eyeglasses dramatically reduce eye exposure during fluoroscopy—leaded eyewear is recommended for personnel who accumulate monthly readings on collar badges greater than 400 mrem (4 Sv). Levels of exposure in this range are typically encountered only in areas where continuous cineangiography is conducted frequently (e.g., the cardiac catheterization laboratory).

Employ Proper Shielding

Only the personnel needed to conduct the procedure should be in the fluoroscopy suite. All personnel should be shielded with lead apronsbefore use of fluoroscopy begins. The practitioner using the fluoroscopy unit should alert everyone in the room that he or she is about to begin and ensure that personnel are shielded. Routine use of thyroid shields can minimize the long-term risk of thyroid cancer. Although protective lead gloves can reduce the exposure of the hands to radiation, they can produce a false sense of security. When leaded gloves are employed and the practitioner’s hands are in the field of exposure, units with ABC will increase their output to compensate for the radiodense leaded gloves and negate their protective effects. Using techniques that eliminate the practitioner’s hands from direct exposure within the x-ray field should be used at all times. Protective eyeglasses are available that dramatically reduce eye exposure during fluoroscopy; leaded eyewear is recommended for practitioners who accumulate monthly readings on collar badges above 400 mrem (4 Sv). Levels of exposure in this range are typically encountered only in areas where continuous cineangiography is conducted frequently (e.g., the cardiac catheterization laboratory).

Radiographs

Although the use of ionizing radiation during pregnancy is somewhat controversial, current scientific evidence suggests that when using high-speed film and a lead apron covering the patient's abdomen, little risk of damage to the fetus occurs. It should be remembered that a charge of providing substandard care could be made if the dentist extracts teeth or provides endodontic therapy without making appropriate radiographs. As a result, when signs of active disease are detected during clinical examination and treatment is planned, diagnostic radiographs should be selected using standard selection criteria (see Chapter 1). As with all treatment decisions, the need for radiographs should be communicated clearly to the patient for her informed consent.

Autopsy on Radioactive Bodies

Opening up the dead body would necessarily release radionuclides that had been inhaled or ingested. Shielding of the pathologist is a concern; this could be achieved by wearing a radiology lead apron (0.5 mm lead or equivalent thickness). Long-handled instruments may be helpful in keeping the extremities away from the radioactive organs. Double gloves, hair and foot covers, splashguards, and fluid-resistant long-sleeved jump suits should be used to minimize radiation risk. A problem of special concern is a cut produced during autopsy. The wound should be debrided and rinsed thoroughly to remove as much radioactivity as possible. Placing plastic-backed paper on the floor around the autopsy table would facilitate decontamination. For similar reasons autopsy instruments must be wrapped in plastic.

7.11.7.2.3 Protective clothing and devices

In nuclear medicine, clothes should be adequate to prevent contamination of the body. The minimum requirement is a laboratory coat and gloves. For work with preparation of radiopharmaceuticals, safety glasses, special shoes, as well as caps and masks used for aseptic work, may be required according to national regulations.

A question frequently asked is whether lead aprons are useful for nuclear medicine work. Some reduction of the effective dose will be achieved in case of radionuclides such as 99mTc, while in case of 18F and 131I, the effect is negligible due to the high energy of the gamma rays. It is therefore a matter of judgment whether a limited dose reduction compensates for the effort of wearing an apron. An option used in some places is to use a lead apron during injection while it is more suitable to use a movable shield when in close contact with the patient during an examination.

Protection in practice

Distance and the use of the inverse square law can easily be overlooked. A single step back from the patient may double the distance and reduce dose by a factor of 4. This can be combined with the time of exposure. Reducing exposure time is clearly important for patient protection, but staff should also minimize the time standing close to the patient.

Because of the substantial difference in scatter from the entrance and exit sides of the patient, it is always better to have the X-ray tube below the patient, because the maximum dose to the operator will then be to the lower part of the body rather than to the upper part including the tissues with the greater radiosensitivities. Overcouch screening tables (with the X-ray tube above the table) should only be used routinely with remote screening from behind a protective screen; they are not suitable for interventional studies. It is also important to ensure that for oblique views the X-ray tube is angled away from the operator so as to minimize exposure to X-rays scattered from the entrance side of the patient.

Protective clothing is invariably required for staff working in the unprotected part of the controlled area while the X-ray beam is on. Lead apron specifications are generally 0.25, 0.35 or 0.5 mm lead equivalent. These transmit approximately 5%, 3% and 1.5%, respectively. The thickness to be used depends on local risk assessments, but as a general rule a radiologist would use a 0.35-mm lead apron for general work and a 0.5-mm lead apron for interventional procedures. A major issue is comfort, and this will be the biggest factor in selecting the style of apron to be used. One important protection issue is to select an apron that can be fully closed at the side; a right-handed radiologist will often have that arm raised and that side of the body turned towards the patient. The weight of the apron can be reduced by having thinner lead on the back; it is unusual for operators to turn their back on the patient. There are also so-called lightweight materials used in lead aprons. These incorporate lower atomic number materials such as barium and tin with K-edges in the mid to lower part of the X-ray spectrum, making them more effective in attenuating X-rays with energies below the K-edge of lead (88 keV). A weight reduction of about 30% is claimed to provide the same protection as a standard lead apron.

Most lead aprons leave the thyroid unprotected because of the added discomfort introduced with a high collar. For high-dose procedures, there may then be a requirement to wear a separate thyroid collar, usually with 0.5 mm lead equivalence. The requirement will be based on a risk assessment and will be included in the local rules. In addition, interventional radiologists may be required to use lead glasses or goggles. It is important that these incorporate protection onthe sides, as it is common practice for radiologists to have their head turned away from the patient to watch the monitor. It is possible to get prescription lead glasses.

Of almost equal importance to personal protective equipment is other shielding incorporated in the X-ray installation. Undercouch fluoroscopy installations have a lead apron attached to the explorator or image intensifier mounting. If the explorator is lowered to the maximum extent and the apron is correctly positioned, the amount of radiation reaching the operator should be minimal. In rooms with fixed C-arm installations, it is common practice to have a lead screen attached to the side of the table to reduce scatter radiation to the legs and feet and to have a shield (incorporating a lead glass screen) mounted on the ceiling. When using these screens, it is important to remember that the source of radiation is scatter from the patient. The screen should be positioned directly between the region being examined and the operator. If a ceiling-mounted screen is used with a lead glass panel and the radiologist is able always to see the part of the patient being examined through that panel, then there should be no need to use lead glasses.