Radiation exposure levels in relatives of patients after radioiodine therapy MEDICAL SCIENCES (2000), 2, 87–90 © 2000 SULTAN QABOOS UNIVERSITY Department of Clinical and Biomedical Physics, College of Medicine, Sultan Qaboos University, P O Box 35 Al-Khod, Muscat 123, Sultanate of Oman. E-mail: haddiab@omantel.net.om. *To whom correspondence should be addressed. 87 Radiation exposure levels in relatives of patients after radioiodine therapy *Bererhi H, Constable A R مستوى األشعاعية ألقارب المرضى بعد العالج باليود المشع أنتوني آونستابل، هاديا البريحي المستشفى بمغادرة للمرضى يسمح واطئ بمستوى هو ،وهل المشــع باليود عالجا تلقوا الذين ىالمرض ألقارب االشعاعي النشاط مستوى تقييم :الهدف :الملخص الدرقية الغدة بسرطان المرضى أقارب من 23 و الدرقية الغدة نشاط بفرط المصابين المرضى أقارب من 47 مراقبة تمت :الطريقة. رقادهم فترة يقلل وبذلك مبكرا :النتائج .المشع اليود بقايا من MBq 30 مستوى على المستشفى في المرضى خروج بعد أشعاعيتهم لقياس أيام، سبعة لمدة المشع باليود المرضى أقاربهم عولج والذين لها ىتعرضالت القليلة االشعاعية للجرعة بالنظر :الخالصة 1mSvر46 أستلم واحدًا طفًال ماعدا mSv 1 من أقل واألطفال األزواج في المقاسة الجرع آانت المستشفى في هم بقاء مدة نختزل وبذلك مبكرا المرضى بخروج يسمح مما صرامة أقل التعليمات جعل الممكن فمن ، األقارب ABSTRACT: Objective – To assess whether the level of radioactivity received by relatives of patients treated with radioiodine (131I) is low enough to allow the patients leave the hospital earlier, thus reducing their hospital stay. Method – Forty seven relatives of thyrotoxic patients and 23 relatives of thyroid cancer patients treated with 131I therapy were monitored for 7 days for radiation after discharging the patients at 30 MBq residual 131I. Results – The doses measured in spouses and children were less than 1 mSv except for one child who received 1.46 mSv. Conclusion – In view of the low radiation doses received by the relatives, regulations could be made less stringent, thus reducing the hospital stay of the patients. KEY WORDS: radioiodine, relatives, radiation, dosimeter adioiodine (131I) is widely accepted as the treat- ment of choice for thyrotoxicosis.1 It is also used for whole body scans and in high doses for ther- apy in differentiated thyroid carcinoma.2 In the United Kingdom, patients receiving 131I ther- apy are nowadays treated as outpatients with some restric- tions on their contact with others if they receive a dose less than 800 MBq. This corresponds to the limit for travel by private transport.3 In the United States, an inter- nally retained activity of 1110 MBq4 is permitted for a patient to be discharged from hospital with timed restric- tions for contact with others. Now the US Regulations are less stringent since they have been updated. 5 For social and cultural reasons regulations in Oman require that patients remain in hospital until the radiation level at one metre from the patient drops to 2 µSv/h. This practice was derived from the UK guidance notes,3 which allow an internal body activity limit of 30 MBq of 131I for returning to radiosensitive work and contact with children. This corresponds to a radiation level at one me- tre from the patient of about 2 µSv/h. Buchan and Brindle have shown that contamination6 and radiation doses7 to relatives of patients receiving up to 800 MBq and discharged as outpatients with appropri- ate instructions, are negligible. The present study was planned to measure the radia- tion dose received by relatives of patients with 30 MBq of 131I in the body at discharge from hospital and without imposing any restrictions on them. The study was under- taken as a first step towards relaxing our rather stringent regulations. METHOD Fourteen patients treated with 131I for thyrotoxicosis and five treated for differentiated carcinomas of the thy- roid (3 therapeutic doses and 2 whole body scans) were selected. The mean (±SD) dose administered for thyro- toxic patients was 489 (±117) MBq (range, 300–670 MBq) and for cancer patients was 2920 (±2500) MBq (range 300–5740 MBq). The duration of hospitalisation varied from 2 to 9 days (mean 5 days) for patients with cancer R B E R E R H I A N D C O N S T A B L E 88 and 9 to 15 days (mean 12 days) for thyrotoxic patients. The patient was discharged when the activity in the body fell below 30 MBq and this was deemed to have occurred when the radiation level at one metre from the erect pa- tient was less than 2 µSv/h. On discharge, all patients in this study were well and self-dependent. The main selection criteria were (a) the patient and family must consent to wearing the dosimeter at all times for 7 days, (b) the patient and relatives should live to- gether during the whole week the dosimeter was worn. In other respects, families were to assume their normal hab- its and sleeping arrangements, which were recorded. The ages of the relatives monitored ranged from 6 months to 60 years. For the dosimeters, Harshaw TLD 200 rods (6 mm x 1 mm dia) made of cadmium fluoride dysprosium were used. For every subject three rods were inserted into a flexible black tube made of silicon rubber with one sealed end. The open end was sealed with a removable plug of black rubber. The tube was then put into a water- tight painted capsule with a screw-in end piece and a cord was threaded into two holes at the extremities of the cap- sule, designed in such a way that, once the cord was in place, the capsule could not be opened (Figure 1). The lengths of the cord were individually adjusted to bring the capsules to the level of the supra-sternal notch. The capsules were placed in individually labelled lead pots, which were then fitted into a wooden box (Figure 2) to- gether with a dosimeter for background measurement. Patients were asked to keep the background dosimeter in a place remote from general living activities. After the capsules were returned the radiation doses were measured with a Harshaw 6600 TLD reader. The ethical committee of our institution approved the study and, after discussion with their relatives, all pa- tients agreed to participate. RESULTS The cumulative radiation dose (µSv) over 7 days re- ceived by the relatives of patients treated with 131I for thyrotoxicosis and carcinoma from the time the patient arrived home are shown in Table 1 and Table 2 respec- tively. The results are presented as mean plus and minus one standard deviation. Statistical significance was deter- mined by applying the Student’s t-test. A p value <0.05 was considered statistically significant. One patient was eliminated from the study because he left home for a 7-day period. Children slept in separate rooms from their parents except for one 7 year-old child who slept in the same bed as her parents. The spouse of each patient slept in the same bed in all cases. In the families of cancer and thyrotoxicosis patients, the spouses received a higher mean dose than the rest of the relatives. In the families of the thyrotoxic patients the spouses received the maximum dose. However, among the families of the cancer patients, it was a child who re- ceived the maximum dose (1.46 µSv). The lowest dose of zero was received by a child looked after by a maid, who also received zero dose. There was no significant difference between the means of the cumulative radiation doses received by rela- tives of our patients with 30 MBq over a 7 day period and the cumulative radiation dose per 30 MBq received by the relatives of Buchan and Brindles’s patients over 21 days. Buchan and Brindle7 measured the cumulative dose FIGURE 1. Capsules showing one mounted on a necklace. FIGURE 2. A wooden box that houses the lead pots containing the capsules. R A D I A T I O N E X P O S U R E T O R E L A T I V E S 89 to family members for 21 days from the time the patient arrived home after administration of 131I doses of 148- 592 MBq on an outpatient basis and to whom no instruc- tions were given to minimise radiation hazards. The re- sults of Buchan and Brindle7 were analysed by Wasserman and Klopper8 and were found to be, on aver- age, for 21 days, 5.6±3.7 µSv.MBq-1 for spouses and 1.5±0.87 µSv.MBq-1 for other family members. Using these figures, the radiation dose to the families if, like ours, their patients had 30 MBq of 131I in their bodies at the time of discharge would be 168±110 µSv for spouses and 45±26 µSv for other family members (Table 3). DISCUSSION There is no evidence that radiation from patients treated with 131I causes problems to other people. More- over, a long-term study9 did not detect any harmful effect in 103 persons, who, when children had been treated with 131I for thyroid carcinoma with a mean dose of 17 GBq and a maximum dose of 26 GBq and were followed for a mean period of 22 years (maximum: 45 years). Neverthe- less, precautions should be taken to avoid unnecessary radiation to others who may come into the vicinity of the patient. To achieve this, patients are usually kept in hospi- tal until their retained activity satisfies the adopted regula- tions: 30 MBq in Oman, 800 MBq for England3 and 1110 MBq for USA.4 Since 1997, the activity retained by the patient in the USA has been unspecified provided no other individual receives a dose exceeding 5 mSv. This means that a patient, treated with more than 7000 MBq of 131I, could leave the hospital subject to certain restric- tions.5 In our institution patients are kept in hospital until they are considered safe for close contact with children. Our study shows that even with this strict restriction the radiation doses to relatives of patients with thyrotoxicosis or carcinoma of the thyroid showed a measurable radia- tion dose. For most relatives this was lower than the ICRP recommended annual limit of 1 mSv except for a one year-old child who received a cumulative dose over 7 days of 1.46 mSv. This child was the youngest in a family we visited on the day of discharge. The entire time we were there (about one hour), the patient held the child in her lap or her shoulder. Apart from this child, spouses received the highest radiation, evidently due to the time they spent close to the patient, particularly during sleep. The fact that the lowest dose was sustained by a child cared by a maid suggests that families with infants should preferably appoint a childminder. This study shows that although we retained our pa- tients until they were considered safe to be with children, the relatives still received doses comparable to the doses documented as received from outpatients,7 in another study, even though that study recorded doses over a pe- riod approximately thrice as long as ours. Unlike in other countries, our patients are not re- leased immediately from hospital, mainly because of the uncertainty regarding their compliance to hospital in- structions in a climate of social and cultural traditions totally different from those of Western urban communi- ties. Traditional close physical contact between mothers and young children cannot be minimised by mere instruc- tions. CONCLUSION While the restrictions practised in our study were intentionally more stringent than necessary, these enabled us to observe and measure the radiation doses to relatives TABLE 1 Cumulative radiation doses received over 7 days by relatives of patients treated with 131I for thyrotoxicosis with 30 MBq body retained activity. Radiation Dose (µSv) Relatives No. Minimum Maximum Mean SD Spouses 13 1 728 221 246 Other 34 0 (child & maid) 253 68 60 TABLE 2. Cumulative radiation doses received over 7 days by relatives of patients treated with 131I for differentiated thyroid carcinoma with 30 MBq body retained activity Radiation Dose (µSv) Relatives No. Minimum Maximum Mean SD Spouses 4 8 665 195 314 Other 19 819 1460 (child) 167 347 TABLE 3 Cumulative radiation doses received by relatives of Buchan and Brindle’s patients treated with 131I for thyrotoxicosis6 calculated for 30 MBq body retained radioactivity. Radiation Dose (µSv) Relatives Number Mean SD Spouses 29 168 110 Other 25 45 26 B E R E R H I A N D C O N S T A B L E 90 at extreme conditions. Our findings enable us to recom- mend significant shortening of the hospital stay of pa- tients treated with 131I. ACKNOWLEDGEMENTS We thank Mr. Hugh Wilkins for his contribution to the implementation of this study. We are also grateful to Mr. Afkar Nadhim Al-Farsi and Mr. Kirthi Jayasekera for their meticulous technical assistance. REFERENCES 1. Solomon B, Glinoer D, Lgasse R, Wartofsky L. Current trends in the management of Grave’s disease. J clin Endocrinol Metab 1990, 70, 1518–24. 2. Freitas JE, Grass MD, Ripley S, Shapiro B. Ra- dionuclide diagnosis and therapy of thyroid cancer. Current status report. Semin Nucl Med 1985, 15, 122–5. 3. HMSO. Guidance notes for the protection of persons against ionizing radiations arising from medical and dental use. London. 1988. 4. US Regulatory Title 10 CFR 35.75. 1986. 5. US Regulatory Title 10 CFR 35.75 1997. 6. Buchan RCT, Brindle JM. Radioiodine therapy to outpatients: the contamination hazard. Brit J Radiol 1970, 43, 479–83. 7. Buchan RCT, Brindle JM. Radioiodine therapy to outpatients: the radiation hazard. Brit J Radiol 1971, 44, 973–5. 8. Wasserman HJ, Klopper JF. Analysis of radiation doses received by public from 131I treatment of thyro- toxic outpatients. Nucl Med Commun 1993, 14, 756–60. 9. Shapiro B, Beierwaltes WH, Guz E et al. 131I treat- ment of thyroid carcinoma in children. Endocrinology. 1986, 119, 119. 10. **Grigsby PW, Siegal BA, Baker S, Eichling JO. Radiation exposure from outpatient radioactive iodine (131I) therapy for thyroid carcinoma. JAMA 2000, 283, 2272–4. Radiation Doses Glossary µSv – microSievert mSv - milliSievert MBq - megaBecqueral GBq – gigaBecqueral mCi - milliCuries **Editor’s Note: This recent study (Ref: 10) has vin- dicated the leniency of the US Regulations by finding the radiation doses received by relatives of 30 outpa- tients treated with large doses of 131.I for thyroid can- cer to be well below the permitted limit of 5.0 mSv. (Reference added at Editor’s discretion.). Radiation exposure levels in relatives of patients �after radioiodine therapy METHOD RESULTS DISCUSSION Table 1 Cumulative radiation doses received over 7 days by relatives of patients treated with 131I for thyrotoxicosis with �30 MBq body retained activity. Table 2. Cumulative radiation doses received over 7 days by relatives of patients treated with 131I for differentiated thyroid �carcinoma with 30 MBq body retained activity CONCLUSION ACKNOWLEDGEMENTS REFERENCES