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1
Department of Radiology, Presbyterian Hospital, 1100 Central Ave. S.E.,
Albuquerque, NM 87106.
2
Radiology Associates of Albuquerque, 5890 Eubank N.E., Albuquerque, NM
87111.
3
Department of Radiology, University of New Mexico, 2211 Lomas Blvd. N.E.
Albuquerque, NM 87131.
4
Department of Radiology, University of Utah Health Sciences Center, 50 N.
Medical Dr., Salt Lake City, UT 84132.
Received March 27, 2001;
accepted after revision July 24, 2001.
Address correspondence to J. N. King.
Abstract
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MATERIALS AND METHODS. A sterile, disposable, lead-free surgical drape containing radiation protection material composed primarily of bismuth was evaluated for effectiveness in reducing radiation doses to health care personnel. Measurements of phantom scatter, patient scatter, skin entrance, and the effects of collimation, together with comparative monthly thermoluminescent dosimeter recordings, were taken to determine the effectiveness of X-ray beam attenuation using the bismuth drapes.
RESULTS. Scatter radiation to physicians, as measured by thermoluminescent dosimeters placed on each eye, the thyroid, and the wrist, was reduced by 12-fold for the eyes, 25-fold for the thyroid, and 29-fold for the hands when the radiation-attenuating surgical drape was used when compared with control studies performed with a standard nonattenuating surgical drape alone. Monthly thermoluminescent dosimeter measurements decreased fourfold in one physician. Using the protective drape reduced exposure to the assistant in each case to negligible levels. Skin entrance dose was not increased unless the protective drape was placed directly in the X-ray beam. An X-ray attenuation factor equivalent to 0.1 mm of lead with 8 x 8 cm collimation reduced the scatter rates from five- to ninefold despite a 30-40% increase in entrance exposure rate as the lead equivalence increased.
CONCLUSION. Depending on the procedure, the height of the practitioner, and the positioning of the radiation-attenuating surgical drape, use of this drape can substantially reduce the radiation dose to personnel with minimal or no additional radiation exposure to the patient.
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Although the recommended limit for radiation workers has not changed greatly since about 1958, the philosophy toward radiation protection and limits has changed dramatically. The limit is now regarded as an upper limit of acceptability. The principle of ALARA (as low as reasonably achievable) is used to ensure that most exposures will be well below the accepted limit. Experience with the ALARA principle and the limit of 5 rem (50 mSv) per year has allowed the average exposure of workers in the United States—with the exception of interventional radiologists and cardiologists—to decline steadily to about 5% of the limit. The increased use of fluoroscopy by anesthesiologists for pain therapy and during radiation therapy procedures has further expanded the risk to health care providers.
Although the acute effects of radiation are not commonly a problem, the stochastic effects of radiation remain a concern. The probability of the occurrence of stochastic effects is directly related to the radiation dose, but the severity of these conditions is not related to the total dose received. Stochastic effects include carcinogenesis and genetic mutation; they are of particular concern because there is no threshold dose below which the radiation-induced effects will not occur. The nonstochastic effects, such as radiation-induced cataracts, do have a threshold dose, and above this threshold the severity is directly related to the dose. Stochastic events are considered to occur at all doses, but the less the frequency, the lower the dose—thus, the principle of ALARA [1, 4, 5, 8,9,10].
This article focuses on the use of a new radiation protection device intended to reduce both the unit dose and the overall level of radiation experienced by radiation workers during interventional radiology procedures.
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Phase 2
Twelve patient studies were performed using extensive placement of
thermoluminescent dosimeters (TLDs). Eight patient studies served as control
studies that were performed with the use of a standard nonattenuating surgical
drape; and the studies of four patients used the radiation-attenuating drape.
The drape was placed on the patient with the window of the drape over the skin
puncture site (Fig. 2). All
patient studies were performed on the same radiographic equipment (Picker,
Cleveland, OH), and all procedures were percutaneous nephrostomy placements
performed from the right side of the patient. The monitor was positioned for
viewing in the same location for all examinations. Two radiologists
participated in each study, with interpretations obtained from nine
physicians. Several physicians participated in more than one patient
evaluation. All physicians used their own type of standard radiation
protection. The 12 patient studies included TLDs placed on the patient and the
operators. A TLD was placed on the skin at the level of the entrance dose of
each of the 12 patients, and on the thyroid, left eye, right eye, and left
wrist of both the primary and the assisting physicians performing the
procedure. The TLDs were positioned outside any radiation-protective covering
such as lead aprons, thyroid shields, or leaded glasses. The TLDs were taped
to the skin immediately lateral to the eye for the eye recordings. Eight
control studies were conducted without the protective drape, and four studies
were completed under similar conditions using the protective drape, for a
total of 108 TLD recordings on the nine participating physicians and the 12
patients.
Phase 3
A single radiologist with consistently excessive TLD measurements was asked
to use the protective drapes routinely. In addition, this physician attempted
to carefully perform collimation during all procedures. TLD measurements were
recorded for 3 months: the first 2 months without the use of the protective
drape, and the last month with the protective drape used in most (but not all)
procedures.
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Phase 2
Patient studies were performed using a drape of uniform thickness and
bismuth content. Scatter radiation to the physicians as measured by the TLDs
placed on the thyroid, each eye, and the wrist was reduced by a factor of 12
for the eyes, 25.8 for the thyroid, and 29.4 for the hands. As evidenced by
the skin entrance doses to the patients, both the control procedures and the
drape-protected procedures were of a braod range of complexity
(Table 2). Because TLDs were
positioned on the skin surface lateral to each eye, the recordings for the
right and left eyes are strikingly different, showing the effect of the skull
on scatter X-ray attenuation (Table
3). Note that with the exception of a single left wrist recording
during an extended fluoroscopic procedure, measurements for the assistant in
each procedure performed with the radiation-attenuating surgical drape were
negligible. Presumably, in this case, the assistant was asked to hold or
position a device close to the primary beam
(Table 2, radiologist 2, left
wrist).
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Phase 3
A single interventional radiologist who had exceptionally high TLD
measurements was given the opportunity to use the protective drapes routinely.
In addition, this physician attempted to improve the use of collimation and to
keep exposure times to a minimum. This individual's TLD measurements decreased
four-fold from the previous 2 months. These results are summarized in
Table 4.
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As interventional radiology procedures increase in complexity, the length of these procedures often increases proportionately, and the physicians and staff are required to be near the patient and the X-ray tube for prolonged periods of fluoroscopic time. It is increasingly common for the fluoroscopy beam to be on for as long as 60 min or more for a given case, and dose rates may be as much as 5 R (1290 µC/kg) per minute. Workers in this environment are increasingly exposed to greater levels of radiation, and the trend is toward more rather than less radiation risk [2, 8, 10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28].
A number of methods have been devised to decrease the radiation dose to medical workers, including radiation-protective aprons, thyroid shields, leaded glasses, and several types of ceiling- or floor-mounted shields [2, 6, 7, 14,15,16,17,18,19, 25,26,27,28]. In addition, radiation-attenuating surgical gloves have been advocated because hand doses are generally greater than doses to other parts of the body [2, 6, 7, 25, 28] (Tables 2 and 3). The combination of forward-scattered X rays, backscattered X rays, and secondary electrons released from the glove material reduces the effectiveness of these radiation-attenuating surgical gloves [7]. Some publications caution that radiation-attenuating gloves should not be relied on as a primary means of radiation protection, and that the first line of defense is to keep the examiner's hands out of the primary beam [2, 6]. Our study supports this point by showing that limiting exposure to the primary beam and decreasing the amount of scatter will markedly decrease the radiation dose not only to the hands (as much as 30-fold) but also to the thyroid (25-fold) and the eyes (12-fold). The radiation exposure to support staff or an assistant may be negligible, even for prolonged and complicated procedures, when the method reported here is used. Given the demand for complex procedures that involve prolonged radiation exposure, reducing the dose to physicians and staff is increasingly important.
The concept of using a radiation protection shield placed on the patient to attenuate the scatter radiation that may reach an operator is not new. Results similar to those presented here have been shown for similar shields produced from lead [15,16,17,18,19]. However, because of the need for universal precautions and the toxic nature of lead, the use of nondisposable lead devices has not proven practical [29,30,31,32,33,34,35]. The use of materials other than lead for radiation shielding has also been thoroughly investigated. The device investigated here is a lead-free, disposable, radiation-protective, and sterile surgical drape that not only allows a sterile surgical barrier but also provides substantial radiation protection to the primary operator (Tables 2,3,4). Because it is lead-free, the device does not raise additional environmental concerns and can be disposed of in the same way as any surgical drape [29,30,31,32]. The results of our study are equally important for support personnel and assistants, who may receive negligible amounts of radiation even during long and complex fluoroscopic procedures when this radiation-protective surgical drape is used (Table 2).
At the time of this writing, the price is approximately $34 per drape, which adds relatively little to the cost of the procedure. Opening the package and positioning the drape on the patient usually takes less than 1 min. Because the drape is radiopaque, it may need to be repositioned from time to time during complex procedures, or it may be removed completely and later replaced if necessary. Because the drape material is flexible, these adjustments can usually be done in a few seconds. However, if the largest area of the drape is initially placed on the side of the patient nearest the operator, the need for repositioning is usually minimal. We believe that the large reduction in radiation dose to the operator is well worth the small amount of time and the relatively little added cost required to use the drape.
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