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Radiation Dose to Patient and Personnel During Extracorporeal Shock Wave Lithotripsy
0022-534 7 /87 /1:l84-0716$02.00/0 THE JOURNAL OF UROLOGY
Vol. 138, October
Copyright (c) 1987 by The Williams & Wilkins Co.
Printed in U.S.A.
RADIATION DOSE TO PATIENT AND PERSONNEL DURING EXTRACORPOREAL SHOCK WAVE LITHOTRIPSY WILLIAM H. BUSH, DOUGLAS JONES
AND
ROBERT P. GIBBONS
From the Sections of Diagnostic Radiology and Urology, Center for Kidney Stone Treatment, The Virginia Mason Clinic and The Virginia Mason Medical Center, and Northwest Medical Physics Center, Seattle, Washington
ABSTRACT
Radiation dose to the patient and personnel was determined during extracorporeal shock wave lithotripsy treatment of 60 patients. Surface radiation dose to the patient's back from the fluoroscopy unit on the side with the kidney stone averaged 10 rem (100 mSv.) per case, although the range was wide (1 to 30 rem). The surface dose from the opposing biplane x-ray unit was less, averaging 5.5 rem (55 mSv.) per case but again with a wide range (0.1 to 21 rem). Exit dose at the lower abdomen averaged 13 mrem. (0.13 mSv.) per case and estimated female gonad dose averaged 100 mrem. (1.2 mSv.). Radiation dose to personnel working in the extracorporeal shock wave lithotripsy suite averaged less than 2 mrem. (0.02 mSv.) per case, making it a procedure that is safe in regard to radiation exposure. (J. Ural., 138: 716-719, 1987) Extracorporeal shock wave lithotripsy (ESWL *) has become the preferred treatment modality for most patients with symptomatic renal and upper ureteral calculi. At some centers ESWL alone is used to treat more than 90 per cent of the patients with symptomatic upper urinary tract stones.' 6 Biplane fluoroscopy is used in the Dornier water bath lithotriptor to localize accurately the calculus in the point of maximal shock wave focus. During treatment of small and/or faintly opacified calculi, especially in large individuals, localization or determination of fragmentation can be difficult, potentially resulting in substantial radiation doses to the patient. Radiation doses to patients and to unit personnel were monitored during treatment of 60 patients with the Dornier extracorporeal shock wave lithotriptor. Determinations were made on the skin surface at the entrance sites of each of the biplane fluoroscopy units and at the exit area on the lower anterior abdomen, corresponding to the level of the female gonads. Unit personnel (urologist, anesthesiologist, nurse and technician) were monitored during treatment and dosimetry about the tub also was obtained.
amount of fluoroscopy plus 400 shocks. The dosimetry responses were similar for both groups. Film badge readings and thermoluminescent dosimeter readings also were similar on patients who were monitored simultaneously with both dosimeters, indicating that the values from the badges were not affected adversely by the shock waves. Only those badges or thermoluminescent dosimeters that were within the fluoroscopic field and identifiable on the fluoroscopic screen during treatment were used to provide exposure data. The data from film badges that had become wet or rotated and were exposed incorrectly during treatment were discarded. Measurement of exposure to personnel. Monitoring of the urologist, anesthesiologist, nurse and technician also was done with either an individual film badge or a pocket dosimeter [quartz-fiber electrometer, range Oto 200 mr. (Oto 51.6 micro C/kg.)§] for each treatment case. These were worn outside of the lead apron at the collar level. The pocket electrometers were read by the radiologist (W. H. B.) and the film badges were sent for reporting after each case.
METHODS AND MATERIALS
Radiation exposure about the lithotriptor tub. Any significant radiation exposure is confined to areas immediately about each of the fluoroscopic units (points 3, 4, 6 and 7, fig. 1 and table 1). Exposure decreases rapidly as one moves away from the tub margin and it declines to almost unmeasurable levels at a distance of 1 meter from the tub. Patient dosimetry. Actual radiation measurements on 60 patients during treatment of symptomatic calculi were obtained using film badges and thermoluminescent dosimeters. There were 37 women and 23 men between 23 and 74 years old (mean age 45 years). Kidney stone sizes varied from 5 to 40 mm. and ureteral calculi varied in size from 5 to 12 mm. Fluoroscopy times for the patients averaged 271 seconds (4½ minutes) with a range of 81 to 694 seconds. Video images ("quick pies") per patient averaged 5 with a range of Oto 25. In-bath radiographs averaged 0.66 per patient with a range of O to 4. Radiation doses for patients are summarized in table 3. Entrance doses on the posterior surface of patients from the stone side fluoroscopic unit were obtained with valid badge measurements from 28 patients. Only those badges that were oriented appropriately within the fluoroscopic field were used
RESULTS
Radiation exposure about the lithotriptor tub. Radiation exposure measurements with a calibrated survey metert were obtained at various points about the treatment tub during radiation exposures with each of the fluoroscopic units (fig. 1, and tables 1 and 2). 7 Actual patient dosimetry. Patient dosimetry was obtained by placing film badges and/or thermoluminescent dosimeters+ (doses reported in millirems, 1 mrem. = 0.01 mSv.) in watertight gloves that were taped on the patient's skin surface on the entrance side of each of the biplane fluoroscopic units (fig. 2). Additionally, measurements were obtained from the lower anterior abdomen (the badge was located approximately 4 cm. above the pubic symphysis corresponding to an exit dose from near the female gonad area). To confirm that the thermoluminescent dosimeter measurements were not being affected by the shock waves, a series of dosimeters was exposed during fluoroscopy only and a second series was exposed to the same Accepted for publication March 11, 1987. Read at annual meeting of American Urological Association, New York, New York, May 18-22, 1986. * Dornier Medical Systems, Inc., Marietta, Georgia t Model 36150, Keithley Instrument Co., Cleveland, Ohio. :j: R. S. Landauer, Glenwood, Illinois.
§ Dosimeter, Cincinnati, Ohio.
716
717
RADIATION DOSE DURING EXTRACORPOREAL SHOCK WAVE LITHOTRIPSY
4
5
r---
'L--2
FIG. 1. Virginia Mason Kidney Stone Center treatment room indicating areas monitored (numbers 2 to 8) during phantom dosimetry. TABLE
1. Phantom dosimetry measurements at various points around
FIG. 2. Cross-section illustration of patient during ESWL shows location of film badges (arrows). Rotated and ovoid configuration of human body raises entrance exposure on stone side (arrow A) and causes lower exposure from fluoroscopy unit on opposite side (arrow B).
the lithotriptor tub and room Station
Distance= 0 (mr./hr.)
Distance = 1 m. (mr./hr.)
0 4.6 1.5 1.3 1.3 4.8 0.2
0 0 0 0 0.1 0 0
2 3 4 5 6 7
8
Stations were established around the water-filled stainless steel tub (fig. 1) and measurements with a Keithley calibrated survey meter were made at rim level (distance = 0) and at 1 meter from the rim (distance = 1 m.). The patient was simulated by a 30 cm. diameter water-filled plastic bottle. Under automatic brightness control the fluoroscopy setting was 90 kVp, 3.2 mA.
TABLE 2.
International System of Units
Exposure
Roentgen (R)
(Coulomb/kg.)
Dose
rad (100 ergs/gm.) rem (rad x Q)
Gray (Gy) (joule/kg.) Sievert (Sv) (Gy x Q)
Dose equivalent
3. Radiation doses to the patient during ESWL
Surface entrance dose, kidney stone side Surface entrance dose, opposite biplane fluoroscopy unit Exit dose at female gonad level
Conversion 1 R = 2.58 X 10-• C/kg. 1 rad = 0.01 Gy 1 rem = 0.01 Sv.
For clinical application to diagnostic x-rays the conversion factor for roentgens to rads is approximately 0.9 and, therefore, 1 roentgen = 0.9 rad. Q = Quality factor: for x-rays Q = 1 and, therefore, 1 rad = 1 rem, 1 Gy = 1 Sv.
in the calculation. The average dose was 10 rem (100 mSv.) with a range of 1.0 to 30.5 rem (10 to 305 mSv.). Entrance doses on the posterior surface from the biplane fluoroscopic unit for the opposite side were calculated from 9 valid measurements. The average dose was 5.5 rem (55 mSv.) with a range of 0.15 to 20.9 rem (1.5 to 209 mSv.). Patient gonadal dose information was estimated from badges placed over the lower anterior abdomen of 22 patients. The average exit surface measurement was 13 mrem. (0.13 mSv.) with a range of 5 to 70 mrem. (0.05 to 0.7 mSv.) (table 3).
Av./Case (mrem.)*
Range (mrem.)
10,000
1,010-30,480
5,500
150-20,900
13
5-70
* 1 mrem. = 0.01 mSv.
TABLE
4. Radiation dose to personnel during renal calculus removal
Radiation quantities and units 7
Conventional Unit
Quantity
TABLE
Urologist Urologist when performing entire percutaneous ultrasonic lithotripsy procedure Anesthesiologist Nurse
Percutaneous Ultrasonic Lithotripsy8• 9 Av./Case (mrem.)
ESWL* Av./Case (mrem.)
10 20
<2 <2
3
<2 <2
4
1 mrem. = 0.01 mSv. * Current study.
Personnel doses. Exposure data for personnel are summarized in table 4. Radiation dose to the urologist during ESWL was obtained either by film badge or pocket electrometer (dosimeter) during 40 cases and the dose averaged less than 2 mrem. (0.02 mSv.) per case, with a range of 1 to 7 mrem. (0.01 to 0.07 mSv.). Radiation dose to the anesthesiologist was obtained similarly during 32 patient treatments and the average dose was less than 3 mrem. (0.03 mSv.) per case, with a range of 1 to 5 mrem. (0.01 to 0.05 mSv.). Radiation dose to the ESWL unit nurse or technician was obtained during 32 patient treatments and the average dose was less than 2 mrem. (0.02 mSv.) per case, with a range of 1 to 2 mrem. (0.01 to 0.02 mSv.).
718
BUSH, JONES AND GIBBONS DISCUSSION
Since ESWL has proved to be so effective in the treatment of symptomatic renal and upper ureteral calculi it is incumbent on those involved with the procedure to have some knowledge of the radiation doses to patients and personnel during its use. Patient and personnel dosimetry reported earlier during percutaneous ultrasonic lithotripsy and percutaneous removal of renal calculi showed high local skin doses to the patient but reasonable gonad doses and acceptable personnel doses. 8 • 9 The radiation doses to patients during this study of ESWL treatment of renal calculi are similar to those from other interventional radiological procedures and less than those incurred during percutaneous stone procedures (tables 3 and 5). As shown in figure 2, during treatment the patient is rotated so that the kidney stone is placed at the focus of shock wave impact, that is the transecting point of the biplane fluoroscopy units. If the patient is large the exterior surface of the patient will be much closer to 1 or both of the x-ray units (principally the stone side unit) and there will be less balloon inflation; therefore, the distance from the focus of the x-ray tube to the skin surface will be shorter. Naturally, this increases the radiation doses. In addition, because of the ovoid body shape, the xray unit on the stone side of the patient generates increased radiation to provide enough photons to the image intensifier (regulated by automatic brightness control). Conversely, radiation from the opposing biplane x-ray unit traverses through a relatively thinner section of the body and, therefore, the entrance dose from that x-ray unit is less. Patient doses during ESWL were less than those incurred during percutaneous removal techniques, such as percutaneous ultrasonic lithotripsy (table 5). 8 As with percutaneous stone removal procedures there was great variability in the amount of fluoroscopy and imaging during ESWL. This ranged from a low of only 81 seconds fluoroscopy to a representative higher amount in 1 patient of 368 seconds fluoroscopy plus 25 video images plus 1 in-bath film. Another patient required 694 seconds of fluoroscopy, although fewer images. Consequently, the range of radiation doses received by patients was wide (table 3). The required amount of imaging and consequent radiation seems to be related primarily to the size of the patient, and the size, number, opacity, location and composition of the calculi. A 1 cm. moderately opaque stone in the renal pelvis of an average-sized or small patient was treated effectively and efficiently with a lower radiation dose. Large, dense calculi required more treatment shocks but they could be visualized and imaged readily. The most difficult cases were those involving faintly opacified calculi, especially in an obese patient. At times initial localization of a calculus to the shock wave focus could be extremely difficult. Pre-procedural placement of a retrograde catheter or Double-J* ureteral stent and in-bath radiographs were helpful in these cases, as was use of the "blastpath" effect. 2' 10• 11 The use of a small (9-inch) television monitor improved image contrast and sharpness, and consultation with the radiologist for assistance with imaging also was helpful in some cases. 12 Fluoroscopy times decreased with increased skill and experience of the ESWL operator. Even when some of the higher doses recorded during this ESWL study are considered it is important to recall that exposure to the skin does not always maintain a direct relationship to the risk of leukemia or cancer. Arithmetic conversions of skin surface dose to specific target organ dose must be made for each irradiation energy and field size. Similarly, for bone marrow and leukemia risk the amount of active marrow irradiated during a specific procedure must be calculated and the relative risk compared to leukemia risk from total body (total bone marrow) dose must be reduced accordingly. 9• 13 Local skin dose values for a small field of x-ray exposure are to be compared to skin exposures from other procedures and not to
* Medical Engineering Corp., New York, New York.
TABLE 5.
Radiation to patients during uroradiological procedures: comparative data Millirems (mrem.) dose Skin Surface
Female Gonad
Excretory urogram, 8
4,000
450-800
CT of abdomen and
4,400
1,400-1,700
views1a, i&---19
Male Gonad 100 50-500
pelvis 13 · 15
Upper gastrointestinal series1s-1s ESWL* Barium enema 15- 19
Percutaneous ultrasonic lithotripsy"
7,000-9,000 10,000 11,000 25,000
10-170
10
1 mrem. = 0.01 mSv. * Current study. t Dosage data estimated from surface measurements.
Recommended annual dose limits (rem) for occupationally exposed personnel according to the International Commission on Radiation Protection, and the National Council on Radiation Protection and Measurements 19- 22
TABLE 6.
International Commission on Radiation Protection (mSv.) Whole body Eye lens Gonads Hands Other tissues
5 15 50 50 50
(50) (150) (500) (500) (500)
National Council on Radiation Protection and Measurements (mSv.) 5 15 15 75 15
(50) (150) (150) (750) (150)
organ or total body values. Radiation dose to an organ from a different x-ray unit position is summated, for example rotational exposure during computerized tomography (CT) scanning, but skin doses at different locations from different x-ray sources are not added together. In our study we found that during ESWL the local skin or surface dose was greater but gonadal dose was less than is necessary for an abdominal CT scan. 13- 15 The skin and gonadal doses are comparable to those from an upper gastrointestinal barium study (table 5). 15- 19 Doses to personnel working in the lithotriptor room are minimal because the water in the tub and the metal tub itself attenuate the radiation substantially (table 1). Measurements around the tub showed that radiation doses 1 meter from the tub were less than one-thirtieth of that at the tub rim. Our personnel continue to wear 0.25 mm. lead-equivalent aprons when moving about the room during fluoroscopy, whereas the urologist sits behind a lucent-leaded shield (0.5 mm. lead equivalent) during operation of the unit and he does not wear a lead apron. The average recorded personnel doses of 2 mrem. per case were, in our opinion, higher than actually incurred based on the room dosimetry measurements; 2 mrem. per case is an artifact of limitation of the measuring devices. Because of this low dose it is a safe procedure for personnel using basic radiation shielding techniques (table 6). 19- 22 CONCLUSION
The Dornier extracorporeal shock wave lithotriptor currently is the preferred treatment modality for nearly all patients with symptomatic kidney stones. Its accuracy depends on biplane fluoroscopy that necessitates radiation to the patient and personnel, and these doses can be kept within acceptable limits. The area exposed on the patient is small and the skin surface dose is similar to that from other interventional radiological procedures. Gonad doses are similar to those from many radiological imaging techniques and they are less than those from
RADIATlOi"'I DOSE DURit•lG ZX'TRACORPOREAL SHOCK.
most interventional -~w·~~,,~ nrnr'Pn:n Radiation doses to personnel are minimal. include Strategies to decrease radiation dose to the use of a retrograde catheter or stent to localize small or faintly opacified calculi, especially in large patients, appropriate fluoroscopic collimation (large or small square field) and minimizing fluoroscopy during positioning of the patient. Ms. Joanna Boatman, Ms. Jenny Lee and Mr. Leonard Gross helped to obtain data for this study, Drs. Roy J. Correa, George E. Brannen, Robert M. Weissman, Donald G. Metcalfe, Robert L. Calhoun, James P. Gasparich and Jeffrey P. Frankel allowed us to include their patients in the study, and Ms. Joann Clifford provided the illustrations. REFERENCES
and 9.
10.
11. 12.
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14.
1. Chaussy, C., Schuller, J., Schmiedt, E., Brandl, H., Jocham, D. and
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7. 8.
Lied!, B.: Extracorporeal shock-wave lithotripsy (ESWL) for treatment of urolithiasis. Urology, suppl. 5, 23: 59, 1984. Gibbons, R. P., Correa, R. J., Brannen, G. E., Weissman, R. M., Metcalfe, D. G. and Bush, W. H.: Extracorporeal shock wave lithotripsy for removal of kidney stones. Bull. Mason Clin., 39: 101, 1985. Bush, W. H., Gibbons, R. P., Lewis, G. P. and Brannen, G. E.: Impact of extracorporeal shock wave lithotripsy on percutaneous stone procedures. Amer. J. Roentgen., 14 7: 89, 1986. LeRoy, A. J.: Mayo Clinic experience. Presented at the annual meeting of the Western Angiographic and Interventional Society, Santa Barbara, California, October 1985. Barbaric, Z. L.: UCLA experience. Presented at the annual meeting of the Western Angiographic and Interventional Society, Santa Barbara, California, October 1985. Tegtmeyer, C. J., Kellum, C. D., Jenkins, A., Gillenwater, J. Y., Way, W. G., Barr, J., Piros, G., Springer, R., Lippert, M. C. and Wyker, A. W.: Extracorporeal shock wave lithotripsy: interventional radiologic solutions to associated problems. Radiology, 161: 587, 1986. Wyckoff, H. 0.: The international system of units (SI). Radiology, 128: 833, 1978. Bush, W. H., Brannen, G. E., Gibbons, R. P., Correa, R. J., Jr. and
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Urol., 132: W. H., Jones, D. and Brannen, G. E.: Radiation dose to
personnel during percutaneous renal calculus removal. Amer. J. Roentgen., 145: 1261, 1985. Eusek, J. R., Bush, W. H., Burnett, L. L. and Gibbons, R. P.: Inbath filming during extracorporeal shock wave lithotripsy. Radiology, 158: 850, 1986. Finlayson, B.: Personal communication, 1986. Bush, W. H. and Gibbons, R. P.: Extracorporeal shockwave lithotripsy: role of the radiologist. Letter to Editor. Radiology, 158: 855, 1986. Finston, R. A.: Radiation hazards and radiation protection. In: Uroradiology: An Integrated Approach. Edited by G. W. Friedland, R. Filly, M. L. Goris, D. Gross, R. L. Kempson, M. Korobkin, B. D. Thurber and J. Walter. New York: Churchill Livingstone, vol. 1, chapt. 7, pp. 179-192, 1983. Evens, R. G. and Mettler, F. A.: National CT use and radiation exposure: United States 1983. Amer. J. Roentgen., 144: 1077, 1985. Judy, P. F. and Zimmerman, R. E.: Dose to critical organs. In: Brigham and Women's Hospital Handbook of Diagnostic Imaging. Edited by B. J. McNeil and H. L. Abrams. Boston: Little, Brown & Co., pp. 318-332, 1986. Burkhart, R. L.: Patient radiation exposure in diagnostic radiology examinations: an overview. Department of Health and Human Services Publication (FDA), 83-8217, pp. 199-214, 1983. Laws, P. W. and Rosenstein, M.: A somatic dose index for diag35: 629, 1978. nostic radiology. Health Gray, J.E., Ragozzino, M. W., Lysel, M. S. and Burke, T. M.: Normalized organ doses for various diagnostic radiologic procedures. Amer. J. Roentgen., 137: 463, 1981. Whalen, J. P. and Balter, S.: Radiation Risks in Medical Imaging. Chicago: Year Book Medical Publishers, pp. 24-32 and 96-97, 1984. Anonymous: Recommendations of the International Commission on Radiological Protection (ICRP publication No. 26). Ann. ICRP, vol. 1, No. 3, 1977. Anonymous: Statement and recommendations of the 1980 Brighton meeting of the ICRP. Ann. ICRP, vol. 4, 1980. National Council on Radiation Protection and Measurements. Basic radiation nn~t.e,rtinn criteria (NCRP report No. 39). Washington, D. C.: Publications, 1971.
Vol. 138, October
Copyright (c) 1987 by The Williams & Wilkins Co.
Printed in U.S.A.
RADIATION DOSE TO PATIENT AND PERSONNEL DURING EXTRACORPOREAL SHOCK WAVE LITHOTRIPSY WILLIAM H. BUSH, DOUGLAS JONES
AND
ROBERT P. GIBBONS
From the Sections of Diagnostic Radiology and Urology, Center for Kidney Stone Treatment, The Virginia Mason Clinic and The Virginia Mason Medical Center, and Northwest Medical Physics Center, Seattle, Washington
ABSTRACT
Radiation dose to the patient and personnel was determined during extracorporeal shock wave lithotripsy treatment of 60 patients. Surface radiation dose to the patient's back from the fluoroscopy unit on the side with the kidney stone averaged 10 rem (100 mSv.) per case, although the range was wide (1 to 30 rem). The surface dose from the opposing biplane x-ray unit was less, averaging 5.5 rem (55 mSv.) per case but again with a wide range (0.1 to 21 rem). Exit dose at the lower abdomen averaged 13 mrem. (0.13 mSv.) per case and estimated female gonad dose averaged 100 mrem. (1.2 mSv.). Radiation dose to personnel working in the extracorporeal shock wave lithotripsy suite averaged less than 2 mrem. (0.02 mSv.) per case, making it a procedure that is safe in regard to radiation exposure. (J. Ural., 138: 716-719, 1987) Extracorporeal shock wave lithotripsy (ESWL *) has become the preferred treatment modality for most patients with symptomatic renal and upper ureteral calculi. At some centers ESWL alone is used to treat more than 90 per cent of the patients with symptomatic upper urinary tract stones.' 6 Biplane fluoroscopy is used in the Dornier water bath lithotriptor to localize accurately the calculus in the point of maximal shock wave focus. During treatment of small and/or faintly opacified calculi, especially in large individuals, localization or determination of fragmentation can be difficult, potentially resulting in substantial radiation doses to the patient. Radiation doses to patients and to unit personnel were monitored during treatment of 60 patients with the Dornier extracorporeal shock wave lithotriptor. Determinations were made on the skin surface at the entrance sites of each of the biplane fluoroscopy units and at the exit area on the lower anterior abdomen, corresponding to the level of the female gonads. Unit personnel (urologist, anesthesiologist, nurse and technician) were monitored during treatment and dosimetry about the tub also was obtained.
amount of fluoroscopy plus 400 shocks. The dosimetry responses were similar for both groups. Film badge readings and thermoluminescent dosimeter readings also were similar on patients who were monitored simultaneously with both dosimeters, indicating that the values from the badges were not affected adversely by the shock waves. Only those badges or thermoluminescent dosimeters that were within the fluoroscopic field and identifiable on the fluoroscopic screen during treatment were used to provide exposure data. The data from film badges that had become wet or rotated and were exposed incorrectly during treatment were discarded. Measurement of exposure to personnel. Monitoring of the urologist, anesthesiologist, nurse and technician also was done with either an individual film badge or a pocket dosimeter [quartz-fiber electrometer, range Oto 200 mr. (Oto 51.6 micro C/kg.)§] for each treatment case. These were worn outside of the lead apron at the collar level. The pocket electrometers were read by the radiologist (W. H. B.) and the film badges were sent for reporting after each case.
METHODS AND MATERIALS
Radiation exposure about the lithotriptor tub. Any significant radiation exposure is confined to areas immediately about each of the fluoroscopic units (points 3, 4, 6 and 7, fig. 1 and table 1). Exposure decreases rapidly as one moves away from the tub margin and it declines to almost unmeasurable levels at a distance of 1 meter from the tub. Patient dosimetry. Actual radiation measurements on 60 patients during treatment of symptomatic calculi were obtained using film badges and thermoluminescent dosimeters. There were 37 women and 23 men between 23 and 74 years old (mean age 45 years). Kidney stone sizes varied from 5 to 40 mm. and ureteral calculi varied in size from 5 to 12 mm. Fluoroscopy times for the patients averaged 271 seconds (4½ minutes) with a range of 81 to 694 seconds. Video images ("quick pies") per patient averaged 5 with a range of Oto 25. In-bath radiographs averaged 0.66 per patient with a range of O to 4. Radiation doses for patients are summarized in table 3. Entrance doses on the posterior surface of patients from the stone side fluoroscopic unit were obtained with valid badge measurements from 28 patients. Only those badges that were oriented appropriately within the fluoroscopic field were used
RESULTS
Radiation exposure about the lithotriptor tub. Radiation exposure measurements with a calibrated survey metert were obtained at various points about the treatment tub during radiation exposures with each of the fluoroscopic units (fig. 1, and tables 1 and 2). 7 Actual patient dosimetry. Patient dosimetry was obtained by placing film badges and/or thermoluminescent dosimeters+ (doses reported in millirems, 1 mrem. = 0.01 mSv.) in watertight gloves that were taped on the patient's skin surface on the entrance side of each of the biplane fluoroscopic units (fig. 2). Additionally, measurements were obtained from the lower anterior abdomen (the badge was located approximately 4 cm. above the pubic symphysis corresponding to an exit dose from near the female gonad area). To confirm that the thermoluminescent dosimeter measurements were not being affected by the shock waves, a series of dosimeters was exposed during fluoroscopy only and a second series was exposed to the same Accepted for publication March 11, 1987. Read at annual meeting of American Urological Association, New York, New York, May 18-22, 1986. * Dornier Medical Systems, Inc., Marietta, Georgia t Model 36150, Keithley Instrument Co., Cleveland, Ohio. :j: R. S. Landauer, Glenwood, Illinois.
§ Dosimeter, Cincinnati, Ohio.
716
717
RADIATION DOSE DURING EXTRACORPOREAL SHOCK WAVE LITHOTRIPSY
4
5
r---
'L--2
FIG. 1. Virginia Mason Kidney Stone Center treatment room indicating areas monitored (numbers 2 to 8) during phantom dosimetry. TABLE
1. Phantom dosimetry measurements at various points around
FIG. 2. Cross-section illustration of patient during ESWL shows location of film badges (arrows). Rotated and ovoid configuration of human body raises entrance exposure on stone side (arrow A) and causes lower exposure from fluoroscopy unit on opposite side (arrow B).
the lithotriptor tub and room Station
Distance= 0 (mr./hr.)
Distance = 1 m. (mr./hr.)
0 4.6 1.5 1.3 1.3 4.8 0.2
0 0 0 0 0.1 0 0
2 3 4 5 6 7
8
Stations were established around the water-filled stainless steel tub (fig. 1) and measurements with a Keithley calibrated survey meter were made at rim level (distance = 0) and at 1 meter from the rim (distance = 1 m.). The patient was simulated by a 30 cm. diameter water-filled plastic bottle. Under automatic brightness control the fluoroscopy setting was 90 kVp, 3.2 mA.
TABLE 2.
International System of Units
Exposure
Roentgen (R)
(Coulomb/kg.)
Dose
rad (100 ergs/gm.) rem (rad x Q)
Gray (Gy) (joule/kg.) Sievert (Sv) (Gy x Q)
Dose equivalent
3. Radiation doses to the patient during ESWL
Surface entrance dose, kidney stone side Surface entrance dose, opposite biplane fluoroscopy unit Exit dose at female gonad level
Conversion 1 R = 2.58 X 10-• C/kg. 1 rad = 0.01 Gy 1 rem = 0.01 Sv.
For clinical application to diagnostic x-rays the conversion factor for roentgens to rads is approximately 0.9 and, therefore, 1 roentgen = 0.9 rad. Q = Quality factor: for x-rays Q = 1 and, therefore, 1 rad = 1 rem, 1 Gy = 1 Sv.
in the calculation. The average dose was 10 rem (100 mSv.) with a range of 1.0 to 30.5 rem (10 to 305 mSv.). Entrance doses on the posterior surface from the biplane fluoroscopic unit for the opposite side were calculated from 9 valid measurements. The average dose was 5.5 rem (55 mSv.) with a range of 0.15 to 20.9 rem (1.5 to 209 mSv.). Patient gonadal dose information was estimated from badges placed over the lower anterior abdomen of 22 patients. The average exit surface measurement was 13 mrem. (0.13 mSv.) with a range of 5 to 70 mrem. (0.05 to 0.7 mSv.) (table 3).
Av./Case (mrem.)*
Range (mrem.)
10,000
1,010-30,480
5,500
150-20,900
13
5-70
* 1 mrem. = 0.01 mSv.
TABLE
4. Radiation dose to personnel during renal calculus removal
Radiation quantities and units 7
Conventional Unit
Quantity
TABLE
Urologist Urologist when performing entire percutaneous ultrasonic lithotripsy procedure Anesthesiologist Nurse
Percutaneous Ultrasonic Lithotripsy8• 9 Av./Case (mrem.)
ESWL* Av./Case (mrem.)
10 20
<2 <2
3
<2 <2
4
1 mrem. = 0.01 mSv. * Current study.
Personnel doses. Exposure data for personnel are summarized in table 4. Radiation dose to the urologist during ESWL was obtained either by film badge or pocket electrometer (dosimeter) during 40 cases and the dose averaged less than 2 mrem. (0.02 mSv.) per case, with a range of 1 to 7 mrem. (0.01 to 0.07 mSv.). Radiation dose to the anesthesiologist was obtained similarly during 32 patient treatments and the average dose was less than 3 mrem. (0.03 mSv.) per case, with a range of 1 to 5 mrem. (0.01 to 0.05 mSv.). Radiation dose to the ESWL unit nurse or technician was obtained during 32 patient treatments and the average dose was less than 2 mrem. (0.02 mSv.) per case, with a range of 1 to 2 mrem. (0.01 to 0.02 mSv.).
718
BUSH, JONES AND GIBBONS DISCUSSION
Since ESWL has proved to be so effective in the treatment of symptomatic renal and upper ureteral calculi it is incumbent on those involved with the procedure to have some knowledge of the radiation doses to patients and personnel during its use. Patient and personnel dosimetry reported earlier during percutaneous ultrasonic lithotripsy and percutaneous removal of renal calculi showed high local skin doses to the patient but reasonable gonad doses and acceptable personnel doses. 8 • 9 The radiation doses to patients during this study of ESWL treatment of renal calculi are similar to those from other interventional radiological procedures and less than those incurred during percutaneous stone procedures (tables 3 and 5). As shown in figure 2, during treatment the patient is rotated so that the kidney stone is placed at the focus of shock wave impact, that is the transecting point of the biplane fluoroscopy units. If the patient is large the exterior surface of the patient will be much closer to 1 or both of the x-ray units (principally the stone side unit) and there will be less balloon inflation; therefore, the distance from the focus of the x-ray tube to the skin surface will be shorter. Naturally, this increases the radiation doses. In addition, because of the ovoid body shape, the xray unit on the stone side of the patient generates increased radiation to provide enough photons to the image intensifier (regulated by automatic brightness control). Conversely, radiation from the opposing biplane x-ray unit traverses through a relatively thinner section of the body and, therefore, the entrance dose from that x-ray unit is less. Patient doses during ESWL were less than those incurred during percutaneous removal techniques, such as percutaneous ultrasonic lithotripsy (table 5). 8 As with percutaneous stone removal procedures there was great variability in the amount of fluoroscopy and imaging during ESWL. This ranged from a low of only 81 seconds fluoroscopy to a representative higher amount in 1 patient of 368 seconds fluoroscopy plus 25 video images plus 1 in-bath film. Another patient required 694 seconds of fluoroscopy, although fewer images. Consequently, the range of radiation doses received by patients was wide (table 3). The required amount of imaging and consequent radiation seems to be related primarily to the size of the patient, and the size, number, opacity, location and composition of the calculi. A 1 cm. moderately opaque stone in the renal pelvis of an average-sized or small patient was treated effectively and efficiently with a lower radiation dose. Large, dense calculi required more treatment shocks but they could be visualized and imaged readily. The most difficult cases were those involving faintly opacified calculi, especially in an obese patient. At times initial localization of a calculus to the shock wave focus could be extremely difficult. Pre-procedural placement of a retrograde catheter or Double-J* ureteral stent and in-bath radiographs were helpful in these cases, as was use of the "blastpath" effect. 2' 10• 11 The use of a small (9-inch) television monitor improved image contrast and sharpness, and consultation with the radiologist for assistance with imaging also was helpful in some cases. 12 Fluoroscopy times decreased with increased skill and experience of the ESWL operator. Even when some of the higher doses recorded during this ESWL study are considered it is important to recall that exposure to the skin does not always maintain a direct relationship to the risk of leukemia or cancer. Arithmetic conversions of skin surface dose to specific target organ dose must be made for each irradiation energy and field size. Similarly, for bone marrow and leukemia risk the amount of active marrow irradiated during a specific procedure must be calculated and the relative risk compared to leukemia risk from total body (total bone marrow) dose must be reduced accordingly. 9• 13 Local skin dose values for a small field of x-ray exposure are to be compared to skin exposures from other procedures and not to
* Medical Engineering Corp., New York, New York.
TABLE 5.
Radiation to patients during uroradiological procedures: comparative data Millirems (mrem.) dose Skin Surface
Female Gonad
Excretory urogram, 8
4,000
450-800
CT of abdomen and
4,400
1,400-1,700
views1a, i&---19
Male Gonad 100 50-500
pelvis 13 · 15
Upper gastrointestinal series1s-1s ESWL* Barium enema 15- 19
Percutaneous ultrasonic lithotripsy"
7,000-9,000 10,000 11,000 25,000
10-170
10
1 mrem. = 0.01 mSv. * Current study. t Dosage data estimated from surface measurements.
Recommended annual dose limits (rem) for occupationally exposed personnel according to the International Commission on Radiation Protection, and the National Council on Radiation Protection and Measurements 19- 22
TABLE 6.
International Commission on Radiation Protection (mSv.) Whole body Eye lens Gonads Hands Other tissues
5 15 50 50 50
(50) (150) (500) (500) (500)
National Council on Radiation Protection and Measurements (mSv.) 5 15 15 75 15
(50) (150) (150) (750) (150)
organ or total body values. Radiation dose to an organ from a different x-ray unit position is summated, for example rotational exposure during computerized tomography (CT) scanning, but skin doses at different locations from different x-ray sources are not added together. In our study we found that during ESWL the local skin or surface dose was greater but gonadal dose was less than is necessary for an abdominal CT scan. 13- 15 The skin and gonadal doses are comparable to those from an upper gastrointestinal barium study (table 5). 15- 19 Doses to personnel working in the lithotriptor room are minimal because the water in the tub and the metal tub itself attenuate the radiation substantially (table 1). Measurements around the tub showed that radiation doses 1 meter from the tub were less than one-thirtieth of that at the tub rim. Our personnel continue to wear 0.25 mm. lead-equivalent aprons when moving about the room during fluoroscopy, whereas the urologist sits behind a lucent-leaded shield (0.5 mm. lead equivalent) during operation of the unit and he does not wear a lead apron. The average recorded personnel doses of 2 mrem. per case were, in our opinion, higher than actually incurred based on the room dosimetry measurements; 2 mrem. per case is an artifact of limitation of the measuring devices. Because of this low dose it is a safe procedure for personnel using basic radiation shielding techniques (table 6). 19- 22 CONCLUSION
The Dornier extracorporeal shock wave lithotriptor currently is the preferred treatment modality for nearly all patients with symptomatic kidney stones. Its accuracy depends on biplane fluoroscopy that necessitates radiation to the patient and personnel, and these doses can be kept within acceptable limits. The area exposed on the patient is small and the skin surface dose is similar to that from other interventional radiological procedures. Gonad doses are similar to those from many radiological imaging techniques and they are less than those from
RADIATlOi"'I DOSE DURit•lG ZX'TRACORPOREAL SHOCK.
most interventional -~w·~~,,~ nrnr'Pn:n Radiation doses to personnel are minimal. include Strategies to decrease radiation dose to the use of a retrograde catheter or stent to localize small or faintly opacified calculi, especially in large patients, appropriate fluoroscopic collimation (large or small square field) and minimizing fluoroscopy during positioning of the patient. Ms. Joanna Boatman, Ms. Jenny Lee and Mr. Leonard Gross helped to obtain data for this study, Drs. Roy J. Correa, George E. Brannen, Robert M. Weissman, Donald G. Metcalfe, Robert L. Calhoun, James P. Gasparich and Jeffrey P. Frankel allowed us to include their patients in the study, and Ms. Joann Clifford provided the illustrations. REFERENCES
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