Exposure of Radiologists During Special Procedures!

[Reprinted from RADIOLOGY, Vol. 104, No.3, Pages 679-683, September, 1972.] Copyrighted 1972 by the Radiological Society of North America, Incorporated

Exposure of Radiologists During Special Procedures!

Radiation Physics

Richard C. Riley, Ph.D., John W. Birks, M.S., Enrique Palacios, M.D., and Arch W. Templeton, M.D. ABSTRAcT-During special procedures, radiologists may receive substantial radiation exposure, especia11y to the unprotected lens of the eye: 92% of a radiologist's exposure at arteriography is due to radiography at the time of contrast medium injection. The mean lens exposure per exam is 5.8 mR for cerebral and 27.1 mR for abdominal arteriograms. Unshielded by the lead apron, a front-co11ar film badge overestimates lens exposure by 20% for cerebral and underestimates by 20% for abdominal arteriograms. Since most exposure occurs during contrast medium injection, manual injection should be avoided whenever possible. INDEX TERMS: sonnel, etc.

Radiations, Injurious Effects, in physicians, radiation per-

Radiology 104: 679-683, September 1972

Siemens Gigantos generator (3-phase, 12-pulse) energized two Machlett DX-60 x-ray tubes (1.0 and 2.0 mm focal spots, 4 mm Al total filtration). Fluoroscopy was single-phase, fullwave on a Machlett DX-60 (1.0 and 0.6 mm focal spots, 3 mm Al total filtration) grid-controlled tube. Radiography was performed using 66-85 kVp; fluoroscopy, 75-100 kVp. A 22.9-cm (9-inch) diameter Philips image intensifier with a gain of 4,000 and automatic brightness control was used. The 875-line TV system was paired with an MTI Vidicon camera. Both film changers were Elema-Schonander AOT 35.6 X 35.6 cm (14 X 14 inches) equipped with 10: 1 grids. Dosimetry: Thermoluminescent dosimeters (Harshaw, TLD-100) were specially selected for a group standard deviation of less than 2%. From this set, matched pairs were selected and remained paired for all measurements. The TLD ribbons were never exposed to more than 1.0 R in order to maintain their sensitivity to extremely small exposures. The annealing cycle was 60 minutes at 400 ° C followed by 150 minutes at 100 ° C; a pre-read annealing was then carried out for 10 minutes at 100° C. We used a Harshaw Model 2,000 TLD reader with a Texas Instrument Company strip chart recorder. The TLD ribbons were calibrated with a Victoreen Model 651 low-energy condenser Rmeter. Calibrations were made by exposing the ribbons to 100 mR from a constant-potential therapy x-ray machine operated at 102 kV with 0.25 mm eu plus 1.0 mm Al added filtration and an h.v.I. of 3.0 mm AI.

receive most radiation exposure during fluoroscopic procedures, primarily due to being absent from the x-ray room during radiography. In special procedures such as arteriography, myelography, and bronchography, he is frequently exposed not only during fluoroscopic placement of the catheter but also during radiography at the time of contrast material injection. Since there is going to be exposure from both sources, the relative importance of each to his overall exposure varies with the nature of the procedure. The lens of the eye and the active bloodforming marrow are both "critical organs" for radiation protection purposes. The lens and approximately 18% of the active blood-forming marrow (4) are not covered by the protective lead apron during special procedures. In the absence of procedure-specific data, concern for the radiologist's exposure could elicit an across-the-board radiation protection recommendation not justifiable for certain procedures. This study was undertaken to determine the exposure to the lens, shoulder, elbow, and hand during individual special-procedure examinations so as to evaluate the adequacy of current radiation protection practices and provide a sound basis for recommending procedural improvements.

D

IAGNOSTIC RADIOLOGISTS

METHODS AND MATERIALS

X-ray Apparatus: All examinations were performed in a single room equipped with conventional under-table fluoroscopy, image intensifier, and TV system, and separate anteroposterior and lateral x-ray tube-film-changer systems. A

1 From the Department of Radiology (R. C. R., Assistant Professor and Head, Division of Radiological Sciences; J. W. B., Research Assistant; E. P., Assistant Professor; A. W. T., Professor and Chairman), University of Kansas Medical Center, Kansas City, Kan. Accepted for publication in April 1972. shan

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RICHARD

C.

RILEY AND OTHERS

TABLE I:

September 1972

EXAMINATIONS MONITORED Number of Exams Monitored

Type of Examination Abdominal arteriography Cerebral arteriography Femoral runoff arteriography Cervico-cephalic arteriography Inferior venacavography Superior venacavography Thoracic aortography Myelography Bronchography

Fig. 1. High-sensitivity TLD-lOO ribbons (0.32 X 0.32 X 0.089 cm). Pairs of ribbons were held in place by a circular Band-aid; the larger Band-aid was then attached to the radiologist.

Procedure: Twelve radiologists were monitored while performing 101 of 418 ~xaminations over a twenty-two-week period (TABLE I). Pairs of TLD's (Fig. 1) were placed on the forehead (lens), collar (attached to the film badge), elbow, and dorsal aspect of the hand. TLD's placed on the palm and shoulder were discontinued because the former was uncomfortable to the radiologists and differed little from the dorsal readings, and the latter gave erroneous readings when partially shielded by a loosely tied apron. Before beginning the examination, TLD's were placed on the radiologist and left on throughout the entire procedure. The monitored radiologist was observed continuously during each procedure and any action which could affect exposure was noted. Total fluoroscopy time, fluoroscopic rnA and kVp, radiographic kVp, mAs, and the number of films were recorded. When tasks were shared by two radiologists (a radiologist and a resident, or two residents) data for the total examination and also for that portion performed by the monitored radiologist were obtained. In these cases, the data were scaled to represent the exposures one radiologist would receive if he had conducted the entire examination. In determining the relative contribution of radiography and fluoroscopy to the total exposure, two sets of TLD's were used. One set was left in place throughout the entire examination; the other was placed on the radiologist immediately prior to each radiographic sequence and removed immediately thereafter. RESULTS

Cerebral and abdominal arteriography comprised nearly half of the examinations monitored. Measured lens exposures were higher

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Monitored Performed

20 26

19.8 25.7

24.4 23.9

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5.9 5.0 1.0 1.0 28.7 4.0

11.2 2.4 0.5 1.0 18.9 5.0

during abdominal arteriography than cerebral arteriography. Fluoroscopy time averaged 6 2/3 minutes for cerebral arteriography, compared to 3 1/3 minutes for abdominal arteriography. However, Figure 2 shows that lens exposure correlates well with total film mAs, as does exposure to the film badge, elbow, and hand. Measurement of the contribution of radiography and fluoroscopy to total exposure indicates that 92% of the radiologist's exposure at each site monitored is due to radiography at the time of contrast material injection. Figure 3 shows the lens exposure per film mAs for other arteriographic procedures. Cervicocephalic arteriograms, inferior venacavograms, peripheral arteriograms, thoracic aortograms, and superior venacavograms are similar to abdominal arteriograms in regard to lens exposure per total film mAs. Since myelography and bronchography do not require the radiologist's presence during radiography, exposure should be entirely due to fluoroscopy (including spot-films). Figure 4 demonstrates good correlation between lens exposure and total fluoroscopic time. Although no radiologist's exposure differed markedly from others for the entire study, variation in individual technique may result in either much larger or smaller exposures than the average during myelography (Fig. 4). The mean exposure to each anatomical location monitored during angiography is given in Figure 5. Similar data are given in Figure 6 for myelography and bronchography. Since abdominal arteriography gives the highest exposure to each anatomical location, four additional renal arteriograms were monitored while contrast material was injected by an automatic, remotely-triggered injector. When the radiologist stood 2-3 m from the patient, lens exposure averaged less than 1.0 mR (0, 0, 3.0, mR); collar exposure was similar (0,0.5,2.0, mR).

°°

Radiation Physics

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EXPOSURE OF RADIOLOGISTS DURING SPECIAL PROCEDURES

Vol. 104

tive and legal difficulties-an approach obviously not to be encouraged. After monitoring radiologists during non-intensified fluoroscopy, Bushong (1-3), recommends that the film badge be worn on the collar (which is not covered by the lead apron), since this anatomical location is expected to receive the highest percentage of applicable MPE. Although many state radiological health agencies offer no advice on the placement of the film badge, Rummerfield noted recently that the California Bureau of Radiological Health believes that the film badge should be worn outside the lead apron (7), a position in agreement with the results of our study. Lens exposure measurements made on unshielded front collars are overestimated by 20% for cerebral arteriography and underestimated by 20% for abdominal arteriography (Fig. 5). For personnel monitoring purposes, these differences are not large enough to warrant special lens monitors. During non-intensified fluoroscopy however, lens exposure measurement at the collar level is reported as overestimated by 2.5 times (2). Special precautions should be observed during contrast-material injection since 92% of a radiologist's exposure occurs at that time. Manual injection of contrast material should be avoided whenever possible--the use of an automatic injector or merely standing 2-3 m back from the patient reduces exposure to barely detectable levels. Stepping away from the patient following manual injection (but before the film sequence has terminated) should significantly reduce ex-

DISCUSSION

Special-procedures radiography may present a greater exposure risk to radiologists than routine fluoroscopy. Although lead aprons are worn and fluoroscopy used in both, the differences are of more consequence than the similarities. The special-procedures radiologist cannot wear lead gloves; lead drapes may have to be removed, and he must be near the patient during contrastmaterial injection. Film-sequence radiography and spot-filming differ primarily in the spatial orientation of scattered radiations due to over- VS. under-table tubes.· Performing only special procedures or neuroradiology, ·and dividing gastrointestinal fluoroscopy among those not thus "specialized" tends to increase the potential for higher exposures among special-procedures radiologists. Based upon the maximum permissible exposure (MPE) of 5 rems/year for the lens, its exposure should not exceed 100 mR/week on the average. Thus a cerebral arteriographer could be limited to 17 procedures per week, an abdominal arteriographer to only 4 or 5 (Fig. 5). Recently, the ICRP (6) re-evaluated the human data on radiation cataracts and reaffirmed its recommendation that the MPE for the lens should be 15 rems/year for low LET radiation. One "solution" to this problem is to wear the film badge under the lead apron and, by thus pretending that the lens and nearly one fifth of the active marrow are not overexposed, film badge readings can be obtained which avoid administra-

48

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Fig. 2. Forehe.ad (lens) exposure vs. total film mAs. Data for films taken at different kVp settings were multiplied by kVp/80. The slopes of the lInes are the total mR per total film mAs for all examinations of a given type. Fig. 3. Foreh~ad (lens) exposure during angiography. The lines for abdominal (A) and cerebral (C) arteriography from Figure 2 are shown: Dat.a p