131I therapy: inpatient or outpatient?

131I Therapy: Inpatient or Outpatient? A widely accepted therapy is 131I for patients with hyperthyroidism caused by Graves’ disease, toxic nodular disease, euthyroid multinodular goiters, and differentiated thyroid carcinomas (1–6). It has been proven to be a safe and a relatively inexpensive treatment modality.131I can lead to complete remission, even in thyroid cancer patients with metastatic disease. Therapeutic doses of131I commonly range from 100 to 7400 MBq, with the larger activities used to ablate thyroid remnants or to treat metastatic disease in patients with thyroid cancer. After a therapeutic administration of 131I, the patient becomes a potential radiation hazard to other individuals. Radiation is emitted from radioactivity in the patient, and radioiodine is secreted in body fluids such as sweat and saliva and excreted into urine and feces. Precautions should be taken to limit the radiation exposure of the nuclear medicine physician, nursing personnel, the patient’s family, and members of the public with whom a treated patient may come in contact. These precautions vary between countries, but recommendations are usually based on measurement of131I retention or instantaneous dose rates. Most patients who receive high doses of131I are isolated in a private room. The patient is monitored daily, and radiation safety precautions are updated as needed. Nursing care and visitors are limited to nonpregnant adults as necessary. The patients are advised against bringing anything with them that they would be unwilling to leave behind should contamination occur. The patient’s radiation exposure is commonly monitored using direct external exposure rate measurements. Alternatively, using fractionated treatment regimens, outpatient treatment schedules have been proposed for large multinodular goiters that commonly require the administration of high doses of 131I (7). In Europe, the administered doses of 131I on an outpatient basis differ among European countries. In Germany, the patient is required to have ,75 MBq on discharge, which is a rather stringent criteria, giving rise to131I tourism to neighboring countries, where criteria for release are less stringent. In the United Kingdom, France, Belgium, and The Netherlands, the maximum permissible radioactivity for ambulatory treatment with radioiodine is between 370 and 740 MBq ( 8). Generally, the amount of radioiodine to be administered has been used as the criterion in determination of the need for hospitalization. This is inaccurate on an individual basis because all 131I-treated patients do not necessarily have the same iodine kinetics. For example, public safety may be better preserved if some patients with toxic goiter who are being treated with 400 MBq131I are hospitalized for longer than some thyroidectomized thyroid cancer patients who receive a much higher ablative dose of 131I because of the rapid clearance of 131I in these thyroid cancer patients. The exposure dose that is considered acceptable for the safety of the general public, resulting from a patient’s treatment, has been reduced in Europe after revised recommendations from the International Commission on Radiological Protection (ICRP). The annual public dose limit is 1 mSv, although adult members of the patient’s family are allowed to receive higher doses, provided that the average over 5 consecutive years does not exceed 1 mSv/y ( 9). Barrington et al. ( 10) recently reported that if hyperthyroid patients who were being treated with 131I (dosage range, 195–800 MBq) on an outpatient basis were given appropriate radiation protection advice, they complied with a 5-mSv dose limit (range, 0.2– 5.8 mSv) for adults in 97% of cases and with a 1-mSv dose limit (range, 0.2– 7.2 mSv) for children in 89% of cases. However, 6 of 17 children, #3 y old, had a dose that exceeded 1 mSv because they were likely to spend more time in close contact with their mothers than was recommended. In the case of parents of children who are $3 y old, the preference is not to treat them as outpatients unless arrangements can made for an alternative caregiver for the child after treatment. Furthermore, outpatients treated with 200, 400, 600, or 800 MBq 131I should be advised to sleep alone for 1, 5, 9, or 12 d, respectively (to comply with a 3-mSv dose constraint), and to avoid contact closer than 1 m with children 3–5 y old for 11, 16, 20, or 22 d or with children.5 y old for 5, 11, 14 or 16 d to comply with a 1-mSv limit. These constraints are suggested in a recent European Commission guidance document in which dose constraints are linked to age ( 11). On the basis of the recommendations for discharge of patients made by the European Commission, the following dose constraints have been proposed or family and close friends: children (including the unborn child), 1 mSv; adults up to 60 y old, 3 mSv; adults . 60 y old, 15 mSv; and third persons or general public, 0.3 mSv. In another study, Barrington et al. ( 12) reported radiation dose rates from patients receiving 131I therapy for thyroid cancer. For a patient who received an ablative dose of 1850 MBq131I, the cumulative dose to nursing staff for a week after treatment depended on patient mobility and was estimated at 0.08 mSv for a self-caring patient to 6.3 mSv for a totally helpless patient. In the follow-up group (residual or recurrent disease), the cumulative doses were Received Feb. 28, 2000; revision accepted Mar. 28, 2000. For correspondence or reprints contact: John M.H. de Klerk, MD, PhD, Department of Nuclear Medicine, University Medical Center Utrecht, Rm. E02.222, P.O. Box 85500, 3508 GA Utrecht, The Netherlands.