Note OCCUPATIONAL EXPOSURE TO
131
I—A CASE STUDY
Maarit Muikku, Jussi Huikari, Helinä Korpela, Carita Lindholm, Wendla Paile, and Teuvo Parviainen*
Abstract—In a laboratory in a company manufacturing radiopharmaceuticals, a laboratory technician was contaminated with 131I. The employee was preparing 131I capsules for thyroid carcinoma treatment. The employee was wearing two pairs of protective gloves and, when changing gloves, noticed a rupture in the right inner glove but no visible rupture in the outer glove. Only 3-4 h later, routine monitoring revealed heavy contamination of the back of the right hand. Immediate actions to decontaminate the hand were taken on-site. Stable iodine was not administered. On the next day, besides persisting heavy contamination of the hand, 131I was also detected in the thyroid gland. Based on original measurements on-site and later follow-up at STUK, including surface contamination measurements and whole body counting, the original 131I activity on the hand was estimated at 12 MBq and the superficial skin dose at 33 Gy, affecting a skin area of about 10 cm2. The thyroid dose was estimated at 430 mGy. Eleven days after the incident, the skin was dry and slightly desquamated. After 15 d, the skin was intact with no desquamation left. No further signs of skin damage have occurred. Cytogenetic analysis of circulating lymphocytes indicated a slight elevation of chromosomal aberrations. Health Phys. 107(4):351–355; 2014 Key words: 131I; contamination; skin dose; thyroid
INTRODUCTION IODINE-131 (131I) is commonly used in medicine for therapy of thyroid cancer, hyperthyreosis, Graves-Basedow disease, toxic adenoma, and also for nuclear medicine imaging. The physical half-life of 131I is 8.02 d (Bé et al. 2008). If radioiodine enters the circulation, whether intentionally or by accident, a substantial fraction is absorbed by the thyroid gland within a few hours. The fraction depends on dietary intake of iodine and on thyroid function. The human biokinetic model applied by the International Commission on Radiological Protection (ICRP) assumes *STUK—Radiation and Nuclear Safety Authority, P.O. Box 14, FIN‐00881, Helsinki, Finland. The authors declare no conflicts of interest. For correspondence contact: Maarit Muikku, STUK—Radiation and Nuclear Safety Authority, P.O. Box 14, FIN‐00881, Helsinki, Finland, or email at [email protected]. (Manuscript accepted 15 April 2014) 0017-9078/14/0 Copyright © 2014 Health Physics Society DOI: 10.1097/HP.0000000000000147
that 30% of iodine in the blood is taken up by the thyroid. The remainder is excreted in urine (ICRP 1997). The biological half-life in blood is about 6 h. Iodine incorporated into the thyroid leaves the gland with a half-life of approximately 80 d, so the effective half life of 131I is determined almost entirely by the physical half-life. Primarily, 131I emits beta particles with a mean energy of 0.18 MeV and a maximum of 0.81 MeV. However, 90% of the beta intensity is from the transition with an end-point energy of 0.61 MeV and an average energy of 0.19 MeV. Most of this energy is absorbed within 0.1 mm, which entails the sensitive basal cell layer of the skin. The contribution to the skin dose from gamma irradiation is very small. For the slightly more energetic beta emitter 170 Tm (Emax 0.97 MeV), a superficial threshold dose of 35 Gy has been estimated for severe acute skin damage (moist desquamation) if the source is larger than 9 mm (Hopewell 1993; ICRP 1991). The threshold dose for late skin atrophy is lower than for acute damage. Although the skin is generally a good barrier against many contaminants, there is evidence that iodine is absorbed through the skin. As an example, dermal exposure to excess iodine, such as povidone-iodine, can induce acute transient hypo- or hyperthyroidism as a toxic effect of iodine overload (ATSDR 2004). Harrison (1963) estimated iodine absorption rates through human skin for solutions of potassium iodide or iodine (I2), and for gaseous I2. He found that the absorption of iodine in aqueous solutions was only in the order of 0.06–0.19% of the amount administered on the skin, whereas for gaseous I2, the absorption was possibly 10 times higher. Washing the skin seemed to remove 80–95% of the activity. Some quantitative information is also available on dermal absorption of iodine in animals. In the studies by Nyiri and Jannitti (1932), quantitative experiments were made on rabbits to evaluate penetration, absorption, and evaporation of iodine applied to the surface of animal skin. According to the studies, 50% of the iodine escapes into the air within the first 2 h. After 24 h, the loss through evaporation amounts to about 75–80%, and subsequently after the first days, it ceases. The remaining approximately 12% penetrates gradually through the skin; 1 to 4% is absorbed
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Copyright © 2014 Health Physics Society. Unauthorized reproduction of this article is prohibited.
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within the first hours, 5 to 6% is taken up within 3 d, and the remaining 3 to 5% is gradually absorbed after this. In a study by Murray (1969), a solution containing a mixture of 85% [131I]I2 and 15% [131I]NaI was applied to a 150 cm2 area of abdominal skin on four miniature pigs. Two hours later, the skin was washed thoroughly, which removed approximately 95% of the applied activity. After 2–3 d, about 1% of the initial activity remained. The peak thyroid uptake of radioiodine was reached 1–2 d after the application. The present study describes an incident of skin contamination with 131I in a company manufacturing radiopharmaceuticals, including activity measurements and dose estimations performed. CASE REPORT AND MONITORING METHODS A female employee was preparing 131I therapy capsules for thyroid carcinoma in a radiopharmaceutical company. The employee was wearing two pairs of protective gloves, and when changing gloves, she noticed a rupture in the right inner nitrile glove but no visible break in the outer latex glove. Only 3–4 h later, when she left the controlled area, routine monitoring revealed heavy contamination of the back of the right hand. The reading of the hand monitor was 2,400 cps. Immediate actions to decontaminate the hand were taken on-site. Washing liquid, KIsolution (0.1 M potassium iodide), and 70% ethanol were used to remove the contamination. After decontamination, the reading of the hand monitor was 1,200 cps. Further washing did not affect the contamination level. Stable iodine was not administered, as the significance of iodine absorption through intact skin was not realized until later. Next morning, about 22 h after the incident, the level of contamination on the back of the right hand was still
October 2014, Volume 107, Number 4
high. Some further actions to decontaminate the hand using washing liquid and warm water were taken. After the decontamination procedures, the reading of the hand monitor was 500 cps. Clearly lower 131I contamination was also noticed on the left hand. The 131I activity in the thyroid was estimated using a NaI scintillation detector (MiniMonitor 900, probe 41; Mini-Instruments Ltd., 8 Station Industrial Estate, Burnham on Crouch, Essex CM0 8RN, UK), resulting in about 120 kBq. At that time, the Radiation and Nuclear Safety Authority (STUK) was notified, and the employee was sent for thyroid and hand monitoring to STUK. At STUK, the surface contamination on the back of the hand was estimated using a NaI scintillation detector (Mini-Monitor 900, probe 42A) and a thyroid monitor (Atomtex RKG-AT1320A; Atomtex, 5 Gikalo St., Minsk, Republic of Belarus; Muikku and Rahola 2007) (Table 1). The maximum dose rate close to the surface of the right hand was measured to be 36 μSv h−1. At this point, the most contaminated skin area was estimated to be approximately 20 cm2. The mobile whole body counter at STUK was also used to monitor the contamination on the hand. The hand was held at a distance of about 60 cm from the HPGe detector. The set-up for hand measurement was later calibrated with a 133Ba thyroid phantom. The use of a thyroid phantom for this purpose is justified since the spot size of the contamination and the physical size of the phantom are very similar. The dose rate near the thyroid gland was measured using dose rate meters (Table 1). The 131I activity in the thyroid was measured using an Atomtex RKG-AT1320A monitor at a distance of 7 cm (Muikku and Rahola 2007) and STUK’s whole body counter (Huikari et al. 2011). The rise in the 131I activity in the thyroid observed on day four is expected if it is assumed that the skin reservoir is feeding the thyroid. The whole body counter was
Table 1. Monitoring results from surface contamination of the back of the right hand and the thyroid (131I) at several postincident time points. Time Hand
Thyroid
29–30 h 4d 11 d 15 d 29–30 h 4d 11 d 15 d 3 mo
Atomtex RGK AT1320 2 MBq 100 kBq
131
I—A CASE STUDY
Maarit Muikku, Jussi Huikari, Helinä Korpela, Carita Lindholm, Wendla Paile, and Teuvo Parviainen*
Abstract—In a laboratory in a company manufacturing radiopharmaceuticals, a laboratory technician was contaminated with 131I. The employee was preparing 131I capsules for thyroid carcinoma treatment. The employee was wearing two pairs of protective gloves and, when changing gloves, noticed a rupture in the right inner glove but no visible rupture in the outer glove. Only 3-4 h later, routine monitoring revealed heavy contamination of the back of the right hand. Immediate actions to decontaminate the hand were taken on-site. Stable iodine was not administered. On the next day, besides persisting heavy contamination of the hand, 131I was also detected in the thyroid gland. Based on original measurements on-site and later follow-up at STUK, including surface contamination measurements and whole body counting, the original 131I activity on the hand was estimated at 12 MBq and the superficial skin dose at 33 Gy, affecting a skin area of about 10 cm2. The thyroid dose was estimated at 430 mGy. Eleven days after the incident, the skin was dry and slightly desquamated. After 15 d, the skin was intact with no desquamation left. No further signs of skin damage have occurred. Cytogenetic analysis of circulating lymphocytes indicated a slight elevation of chromosomal aberrations. Health Phys. 107(4):351–355; 2014 Key words: 131I; contamination; skin dose; thyroid
INTRODUCTION IODINE-131 (131I) is commonly used in medicine for therapy of thyroid cancer, hyperthyreosis, Graves-Basedow disease, toxic adenoma, and also for nuclear medicine imaging. The physical half-life of 131I is 8.02 d (Bé et al. 2008). If radioiodine enters the circulation, whether intentionally or by accident, a substantial fraction is absorbed by the thyroid gland within a few hours. The fraction depends on dietary intake of iodine and on thyroid function. The human biokinetic model applied by the International Commission on Radiological Protection (ICRP) assumes *STUK—Radiation and Nuclear Safety Authority, P.O. Box 14, FIN‐00881, Helsinki, Finland. The authors declare no conflicts of interest. For correspondence contact: Maarit Muikku, STUK—Radiation and Nuclear Safety Authority, P.O. Box 14, FIN‐00881, Helsinki, Finland, or email at [email protected]. (Manuscript accepted 15 April 2014) 0017-9078/14/0 Copyright © 2014 Health Physics Society DOI: 10.1097/HP.0000000000000147
that 30% of iodine in the blood is taken up by the thyroid. The remainder is excreted in urine (ICRP 1997). The biological half-life in blood is about 6 h. Iodine incorporated into the thyroid leaves the gland with a half-life of approximately 80 d, so the effective half life of 131I is determined almost entirely by the physical half-life. Primarily, 131I emits beta particles with a mean energy of 0.18 MeV and a maximum of 0.81 MeV. However, 90% of the beta intensity is from the transition with an end-point energy of 0.61 MeV and an average energy of 0.19 MeV. Most of this energy is absorbed within 0.1 mm, which entails the sensitive basal cell layer of the skin. The contribution to the skin dose from gamma irradiation is very small. For the slightly more energetic beta emitter 170 Tm (Emax 0.97 MeV), a superficial threshold dose of 35 Gy has been estimated for severe acute skin damage (moist desquamation) if the source is larger than 9 mm (Hopewell 1993; ICRP 1991). The threshold dose for late skin atrophy is lower than for acute damage. Although the skin is generally a good barrier against many contaminants, there is evidence that iodine is absorbed through the skin. As an example, dermal exposure to excess iodine, such as povidone-iodine, can induce acute transient hypo- or hyperthyroidism as a toxic effect of iodine overload (ATSDR 2004). Harrison (1963) estimated iodine absorption rates through human skin for solutions of potassium iodide or iodine (I2), and for gaseous I2. He found that the absorption of iodine in aqueous solutions was only in the order of 0.06–0.19% of the amount administered on the skin, whereas for gaseous I2, the absorption was possibly 10 times higher. Washing the skin seemed to remove 80–95% of the activity. Some quantitative information is also available on dermal absorption of iodine in animals. In the studies by Nyiri and Jannitti (1932), quantitative experiments were made on rabbits to evaluate penetration, absorption, and evaporation of iodine applied to the surface of animal skin. According to the studies, 50% of the iodine escapes into the air within the first 2 h. After 24 h, the loss through evaporation amounts to about 75–80%, and subsequently after the first days, it ceases. The remaining approximately 12% penetrates gradually through the skin; 1 to 4% is absorbed
www.health-physics.com
351
Copyright © 2014 Health Physics Society. Unauthorized reproduction of this article is prohibited.
352
Health Physics
within the first hours, 5 to 6% is taken up within 3 d, and the remaining 3 to 5% is gradually absorbed after this. In a study by Murray (1969), a solution containing a mixture of 85% [131I]I2 and 15% [131I]NaI was applied to a 150 cm2 area of abdominal skin on four miniature pigs. Two hours later, the skin was washed thoroughly, which removed approximately 95% of the applied activity. After 2–3 d, about 1% of the initial activity remained. The peak thyroid uptake of radioiodine was reached 1–2 d after the application. The present study describes an incident of skin contamination with 131I in a company manufacturing radiopharmaceuticals, including activity measurements and dose estimations performed. CASE REPORT AND MONITORING METHODS A female employee was preparing 131I therapy capsules for thyroid carcinoma in a radiopharmaceutical company. The employee was wearing two pairs of protective gloves, and when changing gloves, she noticed a rupture in the right inner nitrile glove but no visible break in the outer latex glove. Only 3–4 h later, when she left the controlled area, routine monitoring revealed heavy contamination of the back of the right hand. The reading of the hand monitor was 2,400 cps. Immediate actions to decontaminate the hand were taken on-site. Washing liquid, KIsolution (0.1 M potassium iodide), and 70% ethanol were used to remove the contamination. After decontamination, the reading of the hand monitor was 1,200 cps. Further washing did not affect the contamination level. Stable iodine was not administered, as the significance of iodine absorption through intact skin was not realized until later. Next morning, about 22 h after the incident, the level of contamination on the back of the right hand was still
October 2014, Volume 107, Number 4
high. Some further actions to decontaminate the hand using washing liquid and warm water were taken. After the decontamination procedures, the reading of the hand monitor was 500 cps. Clearly lower 131I contamination was also noticed on the left hand. The 131I activity in the thyroid was estimated using a NaI scintillation detector (MiniMonitor 900, probe 41; Mini-Instruments Ltd., 8 Station Industrial Estate, Burnham on Crouch, Essex CM0 8RN, UK), resulting in about 120 kBq. At that time, the Radiation and Nuclear Safety Authority (STUK) was notified, and the employee was sent for thyroid and hand monitoring to STUK. At STUK, the surface contamination on the back of the hand was estimated using a NaI scintillation detector (Mini-Monitor 900, probe 42A) and a thyroid monitor (Atomtex RKG-AT1320A; Atomtex, 5 Gikalo St., Minsk, Republic of Belarus; Muikku and Rahola 2007) (Table 1). The maximum dose rate close to the surface of the right hand was measured to be 36 μSv h−1. At this point, the most contaminated skin area was estimated to be approximately 20 cm2. The mobile whole body counter at STUK was also used to monitor the contamination on the hand. The hand was held at a distance of about 60 cm from the HPGe detector. The set-up for hand measurement was later calibrated with a 133Ba thyroid phantom. The use of a thyroid phantom for this purpose is justified since the spot size of the contamination and the physical size of the phantom are very similar. The dose rate near the thyroid gland was measured using dose rate meters (Table 1). The 131I activity in the thyroid was measured using an Atomtex RKG-AT1320A monitor at a distance of 7 cm (Muikku and Rahola 2007) and STUK’s whole body counter (Huikari et al. 2011). The rise in the 131I activity in the thyroid observed on day four is expected if it is assumed that the skin reservoir is feeding the thyroid. The whole body counter was
Table 1. Monitoring results from surface contamination of the back of the right hand and the thyroid (131I) at several postincident time points. Time Hand
Thyroid
29–30 h 4d 11 d 15 d 29–30 h 4d 11 d 15 d 3 mo
Atomtex RGK AT1320 2 MBq 100 kBq
