Operational Topics
RADIOACTIVE CONTAMINATION IN HOSPITALS FROM NUCLEAR MEDICINE PATIENTS Shih-Yin Ho and Douglas R. Shearer* al. 1980; Wiatrowski et al. 1984). There is some information concerning contamination hazards arising from therapeutic administration procedures (Brown et al. 1966; Shearer et al. 1985).
Abstvuct-Comparatively little research has been published on radioactive contamination from nuclear medicine patients using hospital toilet facilities. The present study was undertaken to obtain an estimate of the amount of restroom contamination found in a typical 700-bed community hospital as a result of nuclear medicine procedures. Wipe tests were performed on designated areas for two 1-wk periods approximately 6 mo apart. For a typical workload of -25-30 procedures per day, it was found that radioactive contamination ranged from -10’ Bq 100 cm-* 99mTcfor the nuclear medicine for men’s toilet facilities. The restrooms to -lo4 Bq 100 major component of the activity was found in the vicinity of the toilet. Although this contamination is minimal, it is recommended that nuclear medicine patients be directed to designated restroom facilities while awaiting examinations. Health Phys. 62(5):462-466; 1992 Key words: contamination; nuclear medicine; excretion, urinary; 9 9 m T ~
MATERIALS AND METHODS Six bathrooms were chosen for this study, consisting of two patient restrooms in the Nuclear Medicine Department, two public restrooms (a women’s room and a men’s room) located across from the cafeteria on the first floor of the main hospital building, one staff restroom in the Nuclear Medicine Department, and one control restroom located in an office area on the third floor. With the exception of the two public restrooms, all others were unisex. The public restrooms were chosen for comparison with Nuclear Medicine Department restrooms, and, because nuclear medicine patients are advised to drink plenty of fluids while waiting for diagnosis, they often wait in the cafeteria where beverages are available and will use the nearest toilet facilities (two public restrooms). Areas of study included toilet seats, the floor around toilets, sinks, door handles, soap dispensers, toilet roll dispensers, paper towel dispensers, garbage cans, the floor around doors, light switches, flushers, sanitary napkin envelope dispensers, urinals, and the floor around urinals. Over two separate weekly periods approximately 6 mo apart, wipe tests were performed twice a day on these areas for the six restrooms. Alcohol swabs were wiped over approximately 100 cm2 of each of the designated areas and placed into separate test tubes. The tubes were later counted on an Organon Teknika Gamma Counter 7000.+ Individual tubes where radioactivitv exceeded 10 times the background radiation (3.7 x lo-’ Bq 100 cm-2) were reanalyzed on a Canberra multichannel analyzers to determine the identity of the isotope. The detected counts per minute were later converted into absolute radioactivity using a counting efficiency factor determined by counting standards traceable to the National Institute of Standards and Technology.
INTRODUCTION NUCLEAR medicine patients are administered on the order of 108-Bq quantities of radiopharmaceuticals of which a large proportion is excreted in the urine. In many cases, e.g., in bone scan procedures, these patients are encouraged to use hospital restrooms in order to decrease the radiation contribution from nontarget areas during imaging. In addition to radioactivity in urine, radioactivity is also eliminated in sweat and saliva and can be distributed anywhere that is accessible to the touch, e.g., sinks, faucet handles, door knobs. Although there is a great deal of guidance for patients treated with therapeutic quantities of radionuclides (NCRP 1970; WHO 1975; ICRP 1976) and some information on doses to patients given diagnostic radionuclides and the associated external exposure rates (ICRP 1987a, 1987b; NCRP 1982, 1983, 1989a, 1989b),there has been very little research published on the potential for hospital contamination from patients given diagnostic quantities of radionuclides (Eadie et * Medical Physics Department, Rhode Island Hospital, 593 Eddy Street, Providence, RI 02902. (Manuscript received 7 September 199I; revised manuscript received I3 January 1992, accepted 28 January 1992) 0017-9078/92/$3.00/0 Copyright 0 1992 Health Physics Society
(Genesis) 15 wells, Organon Teknika Corp., 100 Akzo Drive, Durham, NC 27704. Series 80 multichannel analyzer, Canberra Industries, Inc., 1 State Street, Meriden, CT 06350.
*
462
Radioactive contamination from nuclear medicine patients 0 S.-Y. Ho AND D. R. SHEARER
463
Table 1. Average number of exams and mean activity of radionuclides (MBq) administered per day. Days of the week Administered Total number of exams 99mTc 20'T1 1231
'''In 1311 1311 0.D.a a
Monday
Tuesday
25 9.8 x 4.4 X 2.2 x 0 1.9 X 5.4 x
28 1.2 x 5.2 X 5.0 x 0 9.3 X 8.0 x
103 10' 10' 10'
10'
104 lo2 10' 10' lo2
Wednesday 30 1.2 x 4.1 X 4.8 x 0 1.9 X 0
104 lo2 10' 10'
Thursday 33 1.2 x lo4 5.6 X 10' 4.6 x 10' 9.3 0 0
Friday 28 1.1 x 6.7 X 2.8 x 0 9.3 x 0
104 10' 10' 10'
Saturday 5 4.2 x 103 0 0 0 9.3 x 10'
Sunday
0 0 0 0
0
0
1 5.2 x
102
0.p. = outpatient.
For a period of several days, dry paper swabs were wiped over the same areas of the nuclear medicine patient and staff restrooms to determine how much of the radioactivity was removable when dry.
RESULTS AND DISCUSSION The contamination in these restrooms was due to "'"TC, as confirmed by the multichannel analyzer. The minimum detectable activity (MDA) of the counting regime used was of the order of lo-' Bq. Therefore, any readings below this level were undetectable. A comparison of removable radioactivity, when using a dry swab as opposed to a wet swab, indicated that wet swabs were considerably more effective in picking up contamination. A preliminary experiment showed that wet swabs picked up 100 times more contamination than did dry swabs. As a result, all tests for removable contamination in this study were conducted using wet swabs. Table 1 gives the patient load and average activity administered during the two separate weekly periods. Table 2 shows the pooled average of the wipe test results for each hospital restroom. The control restroom, located near the offices of the Medical Physics Department¶ showed no counts above the MDA. Removable contamination in the nuclear medicine patient restrooms was about 102-103 Bq 100 cm-2. Greater amounts of removable contamination were found in the public men's restroom located across from the cafeteria. Table 3 shows the average radioactivity for any restroom used by nuclear medicine patients and the mean radioactivity found in various areas of the staff
restroom that were seldom to never used by nuclear medicine patients. The maximum radioactivity found in the staff restroom was of the order of 1 Bq for every 100 cm2 of surface, while the mean radioactivity was only slightly above the MDA for the counter. Fig. 1 shows a comparison of the mean radioactivity is found in various areas of two separate restrooms used primarily by nuclear medicine patients as well as two public restrooms (women's restroom and men's restroom). The error bars show standard deviation. As can be expected, toilet seats, the floor around the toilet, and the flusher have the greatest amounts of removable contamination. The amount of removable contamination in the public restrooms was comparable to the amounts in the nuclear medicine patient restrooms for areas such as the floor around the toilet, the sinks, the door knobs, the soap dispensers, the light switches, and the flushers, but was significantlyless for the toilet seats. The amount of removable contamination for the urinal and the floor around the urinal in the public men's restroom across from the cafeteria was relatively high, on the order of 104-105Bq 100 cm-* for the urinal and the floor around it, respectively. The quantity of radioactivity encountered in a particular restroom depended on the day of the week. Table 4 summarizes the total daily radioactivity on wipes found for all of the tested restrooms combined. There was very little contamination on Sundays, but
Table 3. Average radioactivity found in staff restrooms and restrooms used by nuclear medicine patients. See abbreviation guide in Fin. 1 .a Removable contamination (Bq 100 cm-2)
Table 2. Average radioactivity in a hospital restroom for any dav. See abbreviation guide in Fin. 1 . Restrooms
Removable contamination (Bq 100 cm-2)
Standard deviation
Control Staff N.M. 1 N.M. 2 Women's Men's
No significant counts 5.07 7.22 X 10' 2.18 x 103 2.56 X 10' 2.08 x 104
N/A 5.3 1 . 1 x 103 4.5 x 103 4.7 x 10' 6.0 x 1 0 4
Areas
Staff
Nuclear medicine
6.4 x lo-' (2.8 x lo-') 7.5 x lO'(1.1 x 10') Toilet Floor 7.8 x lo-' (4.7 x lo-') 8.6 (8.95) Sink 6.4 X lo-' (2.7 X lo-') 2.5 (4.4 X lo-') Door 8.3 x lo-' (3.5 x lo-') Soap 6.4 x lo-' (2.7 x lo-') 5.8 x lo-' (1.6 x lo-') Light 5.9 x lo-' (2.2 X lo-') 7.7 X lo-' (2.6 X lo-') Flush 5.6 X lo-' (1.9 X lo-') 1.9 (1.6) a The values in parentheses that follow each measurement are the standard deviations of the measured values. No significant removable contamination.
Health Physics
Mean for N.M. 1
Mean for N.M. 2
Mean for women’s room
c
.-o m .-c:
103
L
Mean for men’s room
EN: S E c 0 0 0 0 0
-a m
102
m0
5
K
10’
100
10‘
Toilet Floor
Sink
Door Soap Light Flush
Urin
FI@
Areas of interest
Abbreviation guide. Abbreviations
Full title
N.M. N.M. 1 N.M. 2 Women’s Men’s Staff Toilet Floor Sink Door Soap Light Flush Urin. Fl@
Nuclear medicine patient restrooms Nuclear medicine patient restroom 1 Nuclear medicine patient restroom 2 Public women’s restroom across from cafeteria Public men’s restroom across from cafeteria Nuclear medicine staff restroom Toilet seat Floor around toilet Sink faucet handles Door knobslhandles Soap dispenser Light switch Flusher Urinal Floor around urinal
Fig. 1. Mean radioactivity found in restrooms mainly used by nuclear medicine patients and restrooms used by the general public.
the contamination level was higher during the week. This is in accordance with nuclear medicine procedural frequency. Nuclear medicine patients are injected with
May 1992, Volume 62, Number 5
radionuclides primarily on weekdays. The fact that Saturdays had some removable contamination could be attributed to two possible reasons: (1) the radioactivity from the weekdays had not decayed completely; (2) some restrooms were still being used on Saturday for nuclear medicine procedures and radionuclide disposal. For the nuclear medicine staff restroom, the contamination was relatively low and essentially constant except for the weekend, when no contamination was found. For the two nuclear medicine patient restrooms tested, although the maximum activity was found on Mondays, the contamination level was fairly constant with the exception of Sundays. For the total daily radioactivity for the public restrooms across from the cafeteria, the radiation was considered low to undetectable on the weekend, was vastly different for men’s and women’s restrooms, and did not exhibit any trend of removable contamination throughout the week. This corresponds to the fact that the radiation detected in these restrooms, notably the men’s room, usually occurs due to a major urine incident at least once a week. The results in this study are not counterintuitive. One would expect nuclear medicine patient restrooms to be contaminated most of the time. Since nuclear medicine patients are advised to drink plenty of fluids, it is expected that the public restrooms near the cafeteria would show occasional contamination. It is expected that the nuclear medicine staff restroom would show some contamination since nurses and other staff are always handling these patients and need to help them dispose of their waste when they are unable to do so. Also, technologists who inject patients with radionuclides may have some contamination on their lab coats (Nishiyama et al. 1980), which also may be transferrable to bathroom surfaces. Removable contamination is expected to occur in restrooms only on the days when testing and injection occur. However, it is reported that 9 9 m Tstill ~ might be present on Saturday, after a week of contamination. It is also expected that public restrooms will not follow any particular trend other than no procedural contamination occurring on the weekends. It may be expected that routine cleaning of the restrooms would remove the contamination; however, everyday custodial cleaning does not. Rather, the effect of normal cleaning and mopping only spreads the contamination. For example, on many occasions when a major incident would occur in the men’s public restroom, wipe tests before the custodial crew arrived would show contamination only in the area of the accident, namely, around the urinal. However, after routine cleaning, wipe tests would show that many areas, if not all areas, on the floor were radioactively contaminated. Thus from these experiences, it seems that normal mopping and cleaning only enhances the spread of contamination rather than removing it. Custodians are required to wear protective gloves when mopping a restroom and are at little risk of being contaminated.
Radioactive contamination from nuclear medicine patients 0 S.-Y.Ho AND D. R. SHEARER
465
Table 4. Total removable contamination (Bq 100 cm-') throughout a week for all restrooms. See abbreviation guide in Fig. 1. Days of the week
a
Restrooms
Monday
All six restrooms together Staff N.M. 1 and 2 (mean) Women's restroom Men's restroom
1.5 X lo3 4.1 4.6 x 103 4.4 9.4
Tuesday 3.7 X 10' 1.6 1.1 x 103 7.4 6.1 X 10'
Wednesday 2.1 X lo4 5.1 2.1 x 102 6.8 X 10' 8.6 X lo4
Thursday 1.4 X lo3 1.3 X 10' 9.3 x 102 6.4 6.2 x lo3
Friday 4.9 X lo2 7.1 1.4 x 103 4.1 X 10' 2.2 X 10'
Saturday 3.7 X lo2
Sunday 1
a
a
2.1 x 103
2.4 2.4
a
a
a
No significant removable contamination.
Table 5. Dose calculated from electron dose-rate factors in skin from radionuclidesdeposited on body surface (calculated from Kocher and Eckerman 1987, Table 1). See abbreviation guide in Fin. 1. Dose from 9 9 m Tdeposited ~ on skin (Sv) Restrooms
Mean e- dose
Max e- dose
Control Staff N.M. Women's restroom Men's restroom
Negligible 1.35 x 10-5 1.58 x lo-* 7.77 x 10-5 1.18 x 10-4
Negligible 1.3 x 10-4 3.18 X lo-' 1.52 x 10-3 2.4 x 10-3
The most common radionuclide used in nuclear medicine procedures is 9 9 m T ~ which , is primarily a gamma emitter with a short half-life of 6.02 h. The action level recommended by the U.S. Nuclear Regulatory Commission for unrestricted areas is 33 Bq 100 cm-' (U.S. NRC 1987), which is often exceeded in the restrooms surve ed here. A contamination level of about 3.7 x 10J Bq cm-2 of gamma-emitting radionuclides transferred to the skin can give rise to doses to the basal layer of between 5 cGy and 10 cGy (Henson 1972). Recent studies have shown that a 3.7 x lo4 Bq cm-' source of uniform contamination of 9 9 m Tgives ~ a dose rate of about 9 mGy h-'(0.9 rad h-') at a 0.007cm depth in skin tissue (McGuire and Dalrymple 1990). It should be noted that the biological significance of small tissue areas irradiated at this level is unclear. Even if 100%ofthe radioactive contamination was transferred to the skin, the amount of radiation to be absorbed (Sv) still would be very low. A toilet seat, for example, is an area where skin will directly touch the surface. Using the dose-rate factors vs. tissue depth results (Kocher and Eckerman 1987) and considering the low amount of removable radioactivity on the seat, the amount of radiation absorbed by the skin is, at most, 3.18 x lo-' Sv in a nuclear medicine patient restroom and practically negligible on other restroom toilet seats (see Table 5). CONCLUSION The radioactivity detected in restrooms is low compared to the amount administered to a patient and the
amount that is excreted. It is interesting to note that much of the contamination cannot be picked up unless the substance touching it is wet. This was shown when dry paper swabs picked up very little or no radioactivity in the restrooms, while alcohol swabs were able to pick up greater amounts. Because of this condition, the hazard from radioactive contamination may be smaller than might be expected from the wipe test results presented here. Although the patients are injected with lo8 Bq of ""'Tc, only -lo4 Bq of removable radioactivity was detected. This is in qualitative agreement with the results of Wiatrowski et al. (1984). This study has shown that the radioactive contamination of hospital restrooms is low and that the hazard is minimal. Contamination that could be absorbed through the skin or by ingestion may give rise to some internal dose. Therefore, it may be prudent to advise nuclear medicine patients to use designated restrooms while waiting for examinations.
-
Acknowledgement($-We would like to thank Glenn Donovan and Sandra Moran at Rhode Island Hospital for their help with this project.
REFERENCES Brown, J. M.; Howley, J. R.; McIntosh, Y. D.; Dickinson, M. B. Contamination problems associated with the administration of massive doses of sulfur-35 to patients. Health Phys. 10:557-561; 1966. Eadie, A. S.; Horton, P. W.; Hilditch, T. E. Monitoring of airborne contamination during the handling of technetium-99m and radioiodine. Phys. Med. Biol. 25: 10791087; 1980. Henson, P. W. A note on some aspects of skin contamination by certain radionuclides in common use. Br. J. Radiol. 45~938-943; 1972. International Commission on Radiological Protection. The handling, storage, use and disposal of unsealed radionuclides in hospitals and medical research establishments. Oxford: Pergamon Press; ICRP Publication No. 25; 1976. International Commission on Radiological Protection. Protection of the patient in nuclear medicine. Oxford: Pergamon Press; ICRP Publication No. 52; 1987a. International Commission on Radiological Protection. Radiation dose to patients from radiopharmaceuticals. Oxford: Pergamon Press; ICRP Publication No. 53; 1987b.
466
Health Physics
Kocher, D. C.; Eckerman, K. F. Electron dose-rate conversion factors for external exposure of the skin from uniformly deposited activity on the body surface. Health Phys. 53: 135-141; 1987. McGuire, E. L.; Dalrymple, G. V. Beta and electron dose calculations to skin due to contamination by common nuclear medicine radionuclides. Health Phys. 58:399-403; 1990. National Council on Radiation Protection and Measurements. Precautions in the management of patients who have received therapeutic amounts of radionuclides. Bethesda, MD: NCRP NCRP Report No. 37; 1970. National Council on Radiation Protection and Measurements. Nuclear medicine-factors influencing the choice and use of radionuclides in diagnosis and therapy. Bethesda, MD: NCRP NCRP Report No. 70; 1982. National Council on Radiation Protection and Measurements. Protection in nuclear medicine and ultrasound procedures in children. Bethesda, MD: NCRP; NCRP Report No. 73; 1983. National Council on Radiation Protection and Measurements. Exposure of the U.S. population from diagnostic
May 1992, Volume 62, Number 5 medical radiation. Bethesda, MD: NCRP; NCRP Report No. 100; 1989a. National Council on Radiation Protection and Measurements. Radiation protection for medical and allied health personnel. Bethesda, MD: NCRP NCRP Report No. 105; 1989b. Nishiyama, H.; Lukes, S. J.; Feller, P. A.; Van Tuinen, R. J.; Williams, C. C.; Saenger, E. L. Survey of 9 9 m Tcontami~ nation of laboratory personnel: Its degree and routes. Radiology 135:467-471; 1980. Shearer, D. R.; Donovan, G. L.; Moore, M. M. Contamination from therapeutic I- 131 capsules. Health Phys. 49:8 183; 1985. US. Nuclear Regulatory Commission. Guide for the preparation of applications for medical programs. Washington, DC: U.S. NRC; Guide 10.8, Revision 2; 1987. Wiatrowski, W. A.; Cooke, E. P.; Kopp, D. T.; Jordan, D. W. Radiocontamination in medical centers from diagnostic nuclear medicine procedures. Health Phys. 47:297-298; 1984. World Health Organization. Manual on radiation protection in hospitals and general practice. Vol. 2. Unsealed sources. Geneva: World Health Organization; 1975.
..
RADIOACTIVE CONTAMINATION IN HOSPITALS FROM NUCLEAR MEDICINE PATIENTS Shih-Yin Ho and Douglas R. Shearer* al. 1980; Wiatrowski et al. 1984). There is some information concerning contamination hazards arising from therapeutic administration procedures (Brown et al. 1966; Shearer et al. 1985).
Abstvuct-Comparatively little research has been published on radioactive contamination from nuclear medicine patients using hospital toilet facilities. The present study was undertaken to obtain an estimate of the amount of restroom contamination found in a typical 700-bed community hospital as a result of nuclear medicine procedures. Wipe tests were performed on designated areas for two 1-wk periods approximately 6 mo apart. For a typical workload of -25-30 procedures per day, it was found that radioactive contamination ranged from -10’ Bq 100 cm-* 99mTcfor the nuclear medicine for men’s toilet facilities. The restrooms to -lo4 Bq 100 major component of the activity was found in the vicinity of the toilet. Although this contamination is minimal, it is recommended that nuclear medicine patients be directed to designated restroom facilities while awaiting examinations. Health Phys. 62(5):462-466; 1992 Key words: contamination; nuclear medicine; excretion, urinary; 9 9 m T ~
MATERIALS AND METHODS Six bathrooms were chosen for this study, consisting of two patient restrooms in the Nuclear Medicine Department, two public restrooms (a women’s room and a men’s room) located across from the cafeteria on the first floor of the main hospital building, one staff restroom in the Nuclear Medicine Department, and one control restroom located in an office area on the third floor. With the exception of the two public restrooms, all others were unisex. The public restrooms were chosen for comparison with Nuclear Medicine Department restrooms, and, because nuclear medicine patients are advised to drink plenty of fluids while waiting for diagnosis, they often wait in the cafeteria where beverages are available and will use the nearest toilet facilities (two public restrooms). Areas of study included toilet seats, the floor around toilets, sinks, door handles, soap dispensers, toilet roll dispensers, paper towel dispensers, garbage cans, the floor around doors, light switches, flushers, sanitary napkin envelope dispensers, urinals, and the floor around urinals. Over two separate weekly periods approximately 6 mo apart, wipe tests were performed twice a day on these areas for the six restrooms. Alcohol swabs were wiped over approximately 100 cm2 of each of the designated areas and placed into separate test tubes. The tubes were later counted on an Organon Teknika Gamma Counter 7000.+ Individual tubes where radioactivitv exceeded 10 times the background radiation (3.7 x lo-’ Bq 100 cm-2) were reanalyzed on a Canberra multichannel analyzers to determine the identity of the isotope. The detected counts per minute were later converted into absolute radioactivity using a counting efficiency factor determined by counting standards traceable to the National Institute of Standards and Technology.
INTRODUCTION NUCLEAR medicine patients are administered on the order of 108-Bq quantities of radiopharmaceuticals of which a large proportion is excreted in the urine. In many cases, e.g., in bone scan procedures, these patients are encouraged to use hospital restrooms in order to decrease the radiation contribution from nontarget areas during imaging. In addition to radioactivity in urine, radioactivity is also eliminated in sweat and saliva and can be distributed anywhere that is accessible to the touch, e.g., sinks, faucet handles, door knobs. Although there is a great deal of guidance for patients treated with therapeutic quantities of radionuclides (NCRP 1970; WHO 1975; ICRP 1976) and some information on doses to patients given diagnostic radionuclides and the associated external exposure rates (ICRP 1987a, 1987b; NCRP 1982, 1983, 1989a, 1989b),there has been very little research published on the potential for hospital contamination from patients given diagnostic quantities of radionuclides (Eadie et * Medical Physics Department, Rhode Island Hospital, 593 Eddy Street, Providence, RI 02902. (Manuscript received 7 September 199I; revised manuscript received I3 January 1992, accepted 28 January 1992) 0017-9078/92/$3.00/0 Copyright 0 1992 Health Physics Society
(Genesis) 15 wells, Organon Teknika Corp., 100 Akzo Drive, Durham, NC 27704. Series 80 multichannel analyzer, Canberra Industries, Inc., 1 State Street, Meriden, CT 06350.
*
462
Radioactive contamination from nuclear medicine patients 0 S.-Y. Ho AND D. R. SHEARER
463
Table 1. Average number of exams and mean activity of radionuclides (MBq) administered per day. Days of the week Administered Total number of exams 99mTc 20'T1 1231
'''In 1311 1311 0.D.a a
Monday
Tuesday
25 9.8 x 4.4 X 2.2 x 0 1.9 X 5.4 x
28 1.2 x 5.2 X 5.0 x 0 9.3 X 8.0 x
103 10' 10' 10'
10'
104 lo2 10' 10' lo2
Wednesday 30 1.2 x 4.1 X 4.8 x 0 1.9 X 0
104 lo2 10' 10'
Thursday 33 1.2 x lo4 5.6 X 10' 4.6 x 10' 9.3 0 0
Friday 28 1.1 x 6.7 X 2.8 x 0 9.3 x 0
104 10' 10' 10'
Saturday 5 4.2 x 103 0 0 0 9.3 x 10'
Sunday
0 0 0 0
0
0
1 5.2 x
102
0.p. = outpatient.
For a period of several days, dry paper swabs were wiped over the same areas of the nuclear medicine patient and staff restrooms to determine how much of the radioactivity was removable when dry.
RESULTS AND DISCUSSION The contamination in these restrooms was due to "'"TC, as confirmed by the multichannel analyzer. The minimum detectable activity (MDA) of the counting regime used was of the order of lo-' Bq. Therefore, any readings below this level were undetectable. A comparison of removable radioactivity, when using a dry swab as opposed to a wet swab, indicated that wet swabs were considerably more effective in picking up contamination. A preliminary experiment showed that wet swabs picked up 100 times more contamination than did dry swabs. As a result, all tests for removable contamination in this study were conducted using wet swabs. Table 1 gives the patient load and average activity administered during the two separate weekly periods. Table 2 shows the pooled average of the wipe test results for each hospital restroom. The control restroom, located near the offices of the Medical Physics Department¶ showed no counts above the MDA. Removable contamination in the nuclear medicine patient restrooms was about 102-103 Bq 100 cm-2. Greater amounts of removable contamination were found in the public men's restroom located across from the cafeteria. Table 3 shows the average radioactivity for any restroom used by nuclear medicine patients and the mean radioactivity found in various areas of the staff
restroom that were seldom to never used by nuclear medicine patients. The maximum radioactivity found in the staff restroom was of the order of 1 Bq for every 100 cm2 of surface, while the mean radioactivity was only slightly above the MDA for the counter. Fig. 1 shows a comparison of the mean radioactivity is found in various areas of two separate restrooms used primarily by nuclear medicine patients as well as two public restrooms (women's restroom and men's restroom). The error bars show standard deviation. As can be expected, toilet seats, the floor around the toilet, and the flusher have the greatest amounts of removable contamination. The amount of removable contamination in the public restrooms was comparable to the amounts in the nuclear medicine patient restrooms for areas such as the floor around the toilet, the sinks, the door knobs, the soap dispensers, the light switches, and the flushers, but was significantlyless for the toilet seats. The amount of removable contamination for the urinal and the floor around the urinal in the public men's restroom across from the cafeteria was relatively high, on the order of 104-105Bq 100 cm-* for the urinal and the floor around it, respectively. The quantity of radioactivity encountered in a particular restroom depended on the day of the week. Table 4 summarizes the total daily radioactivity on wipes found for all of the tested restrooms combined. There was very little contamination on Sundays, but
Table 3. Average radioactivity found in staff restrooms and restrooms used by nuclear medicine patients. See abbreviation guide in Fin. 1 .a Removable contamination (Bq 100 cm-2)
Table 2. Average radioactivity in a hospital restroom for any dav. See abbreviation guide in Fin. 1 . Restrooms
Removable contamination (Bq 100 cm-2)
Standard deviation
Control Staff N.M. 1 N.M. 2 Women's Men's
No significant counts 5.07 7.22 X 10' 2.18 x 103 2.56 X 10' 2.08 x 104
N/A 5.3 1 . 1 x 103 4.5 x 103 4.7 x 10' 6.0 x 1 0 4
Areas
Staff
Nuclear medicine
6.4 x lo-' (2.8 x lo-') 7.5 x lO'(1.1 x 10') Toilet Floor 7.8 x lo-' (4.7 x lo-') 8.6 (8.95) Sink 6.4 X lo-' (2.7 X lo-') 2.5 (4.4 X lo-') Door 8.3 x lo-' (3.5 x lo-') Soap 6.4 x lo-' (2.7 x lo-') 5.8 x lo-' (1.6 x lo-') Light 5.9 x lo-' (2.2 X lo-') 7.7 X lo-' (2.6 X lo-') Flush 5.6 X lo-' (1.9 X lo-') 1.9 (1.6) a The values in parentheses that follow each measurement are the standard deviations of the measured values. No significant removable contamination.
Health Physics
Mean for N.M. 1
Mean for N.M. 2
Mean for women’s room
c
.-o m .-c:
103
L
Mean for men’s room
EN: S E c 0 0 0 0 0
-a m
102
m0
5
K
10’
100
10‘
Toilet Floor
Sink
Door Soap Light Flush
Urin
FI@
Areas of interest
Abbreviation guide. Abbreviations
Full title
N.M. N.M. 1 N.M. 2 Women’s Men’s Staff Toilet Floor Sink Door Soap Light Flush Urin. Fl@
Nuclear medicine patient restrooms Nuclear medicine patient restroom 1 Nuclear medicine patient restroom 2 Public women’s restroom across from cafeteria Public men’s restroom across from cafeteria Nuclear medicine staff restroom Toilet seat Floor around toilet Sink faucet handles Door knobslhandles Soap dispenser Light switch Flusher Urinal Floor around urinal
Fig. 1. Mean radioactivity found in restrooms mainly used by nuclear medicine patients and restrooms used by the general public.
the contamination level was higher during the week. This is in accordance with nuclear medicine procedural frequency. Nuclear medicine patients are injected with
May 1992, Volume 62, Number 5
radionuclides primarily on weekdays. The fact that Saturdays had some removable contamination could be attributed to two possible reasons: (1) the radioactivity from the weekdays had not decayed completely; (2) some restrooms were still being used on Saturday for nuclear medicine procedures and radionuclide disposal. For the nuclear medicine staff restroom, the contamination was relatively low and essentially constant except for the weekend, when no contamination was found. For the two nuclear medicine patient restrooms tested, although the maximum activity was found on Mondays, the contamination level was fairly constant with the exception of Sundays. For the total daily radioactivity for the public restrooms across from the cafeteria, the radiation was considered low to undetectable on the weekend, was vastly different for men’s and women’s restrooms, and did not exhibit any trend of removable contamination throughout the week. This corresponds to the fact that the radiation detected in these restrooms, notably the men’s room, usually occurs due to a major urine incident at least once a week. The results in this study are not counterintuitive. One would expect nuclear medicine patient restrooms to be contaminated most of the time. Since nuclear medicine patients are advised to drink plenty of fluids, it is expected that the public restrooms near the cafeteria would show occasional contamination. It is expected that the nuclear medicine staff restroom would show some contamination since nurses and other staff are always handling these patients and need to help them dispose of their waste when they are unable to do so. Also, technologists who inject patients with radionuclides may have some contamination on their lab coats (Nishiyama et al. 1980), which also may be transferrable to bathroom surfaces. Removable contamination is expected to occur in restrooms only on the days when testing and injection occur. However, it is reported that 9 9 m Tstill ~ might be present on Saturday, after a week of contamination. It is also expected that public restrooms will not follow any particular trend other than no procedural contamination occurring on the weekends. It may be expected that routine cleaning of the restrooms would remove the contamination; however, everyday custodial cleaning does not. Rather, the effect of normal cleaning and mopping only spreads the contamination. For example, on many occasions when a major incident would occur in the men’s public restroom, wipe tests before the custodial crew arrived would show contamination only in the area of the accident, namely, around the urinal. However, after routine cleaning, wipe tests would show that many areas, if not all areas, on the floor were radioactively contaminated. Thus from these experiences, it seems that normal mopping and cleaning only enhances the spread of contamination rather than removing it. Custodians are required to wear protective gloves when mopping a restroom and are at little risk of being contaminated.
Radioactive contamination from nuclear medicine patients 0 S.-Y.Ho AND D. R. SHEARER
465
Table 4. Total removable contamination (Bq 100 cm-') throughout a week for all restrooms. See abbreviation guide in Fig. 1. Days of the week
a
Restrooms
Monday
All six restrooms together Staff N.M. 1 and 2 (mean) Women's restroom Men's restroom
1.5 X lo3 4.1 4.6 x 103 4.4 9.4
Tuesday 3.7 X 10' 1.6 1.1 x 103 7.4 6.1 X 10'
Wednesday 2.1 X lo4 5.1 2.1 x 102 6.8 X 10' 8.6 X lo4
Thursday 1.4 X lo3 1.3 X 10' 9.3 x 102 6.4 6.2 x lo3
Friday 4.9 X lo2 7.1 1.4 x 103 4.1 X 10' 2.2 X 10'
Saturday 3.7 X lo2
Sunday 1
a
a
2.1 x 103
2.4 2.4
a
a
a
No significant removable contamination.
Table 5. Dose calculated from electron dose-rate factors in skin from radionuclidesdeposited on body surface (calculated from Kocher and Eckerman 1987, Table 1). See abbreviation guide in Fin. 1. Dose from 9 9 m Tdeposited ~ on skin (Sv) Restrooms
Mean e- dose
Max e- dose
Control Staff N.M. Women's restroom Men's restroom
Negligible 1.35 x 10-5 1.58 x lo-* 7.77 x 10-5 1.18 x 10-4
Negligible 1.3 x 10-4 3.18 X lo-' 1.52 x 10-3 2.4 x 10-3
The most common radionuclide used in nuclear medicine procedures is 9 9 m T ~ which , is primarily a gamma emitter with a short half-life of 6.02 h. The action level recommended by the U.S. Nuclear Regulatory Commission for unrestricted areas is 33 Bq 100 cm-' (U.S. NRC 1987), which is often exceeded in the restrooms surve ed here. A contamination level of about 3.7 x 10J Bq cm-2 of gamma-emitting radionuclides transferred to the skin can give rise to doses to the basal layer of between 5 cGy and 10 cGy (Henson 1972). Recent studies have shown that a 3.7 x lo4 Bq cm-' source of uniform contamination of 9 9 m Tgives ~ a dose rate of about 9 mGy h-'(0.9 rad h-') at a 0.007cm depth in skin tissue (McGuire and Dalrymple 1990). It should be noted that the biological significance of small tissue areas irradiated at this level is unclear. Even if 100%ofthe radioactive contamination was transferred to the skin, the amount of radiation to be absorbed (Sv) still would be very low. A toilet seat, for example, is an area where skin will directly touch the surface. Using the dose-rate factors vs. tissue depth results (Kocher and Eckerman 1987) and considering the low amount of removable radioactivity on the seat, the amount of radiation absorbed by the skin is, at most, 3.18 x lo-' Sv in a nuclear medicine patient restroom and practically negligible on other restroom toilet seats (see Table 5). CONCLUSION The radioactivity detected in restrooms is low compared to the amount administered to a patient and the
amount that is excreted. It is interesting to note that much of the contamination cannot be picked up unless the substance touching it is wet. This was shown when dry paper swabs picked up very little or no radioactivity in the restrooms, while alcohol swabs were able to pick up greater amounts. Because of this condition, the hazard from radioactive contamination may be smaller than might be expected from the wipe test results presented here. Although the patients are injected with lo8 Bq of ""'Tc, only -lo4 Bq of removable radioactivity was detected. This is in qualitative agreement with the results of Wiatrowski et al. (1984). This study has shown that the radioactive contamination of hospital restrooms is low and that the hazard is minimal. Contamination that could be absorbed through the skin or by ingestion may give rise to some internal dose. Therefore, it may be prudent to advise nuclear medicine patients to use designated restrooms while waiting for examinations.
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Acknowledgement($-We would like to thank Glenn Donovan and Sandra Moran at Rhode Island Hospital for their help with this project.
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