Radiation Exposure Levels in Family Members of Omani Patients with Thyrotoxicosis Treated with Radioiodine (¹³¹I) as Outpatients

Abstract

Objectives:

This study was conducted to assess whether the radiation exposure levels of Omani family members of thyrotoxic patients, if treated with radioiodine therapy as outpatients, are within the international and local radiation dose limits in order to allow them to be treated as outpatients.

Methods:

The study included 86 family members of 22 self-dependent thyrotoxic patients (29 children ≤ 16 yrs and 57 adults including 11 spouses and 8 parents). The mean age of the family members was 26.6 years (range 17 months - 75 years).They were treated with ¹³¹I as outpatients and monitored for 10 days in 2007–2008 for radiation exposure using thermoluminescent dosimeters (TLDs). The mean administered activity of ¹³¹I to patients (±SD) was 610 ±79MBq in the range 520–862 MBq. Oral and written radiation safety instructions were given to patients and family members before leaving the hospital.

Results:

The radiation doses received by family members were less than the annual recommended dose limit for general public of 1mSv, except for four children aged 19 months, 12, 13 and 15 years, who received radiation doses of 2.9, 1.2, 1.2 and 1.2 mSv respectively.

Conclusion:

In view of the low radiation doses received by the family members, we recommend treating thyrotoxic patients undergoing radioiodine therapy with administered activities up to 800 MBq as outpatients.

Advances in Knowledge

1. This study show that, with good radiation safety instructions to patients and relatives, thyrotoxic patients may be treated as outpatients provided the patient is physically and mentally fit to comply with the given instructions and that factors such as travelling distance, socio-economic conditions and family life style are taken into account.

Application to Patient Care

Treating thyrotoxic patients, receiving radioiodine therapy, as outpatients will:

1. Avoid the isolation of these patients with all of its complications. Patients will be more comfortable in their own surroundings with their families.

2. Outpatient treatment will reduce waiting lists allowing greater patient throughput This will lead to greater patient comfort and satisfaction.

Radioiodine therapy, proven to be safe and relatively inexpensive, has been widely used over decades for the treatment of thyrotoxicosis.1,2 However, there are some radiation protection concerns associated with the treatment. In addition to beta particle emissions, ¹³¹I emits penetrating ionizing γ-radiation of 364keV. The therapeutic administration of ¹³¹I makes the patient a source of radiation exposure and a potential radiation hazard to individuals in their surroundings.1,2 Radiation doses received by the public and family members are received through internal contamination as a result of excreted radioiodine or through external exposure which remains the main concern.3,4 To protect relatives from these radiation exposures, patients are admitted in radioiodine therapy wards for different lengths of time according to local regulations.

Nowadays, most countries treat thyrotoxic patients as outpatients. This is done provided they are given appropriate radiation safety instructions to limit the radiation exposures to their family members, particularly to children and pregnant women and the public, to 1.0mSv per year as recommended by the International Commission of Radiological Protection (ICRP).5 However, higher radiation doses received by adult family members are acceptable as long as the average dose of five consecutive years does not exceed 5mSv.5 These limits are also implemented in Oman. The criteria for treating these patients as outpatients are based on the following conditions: a) administered activity should be less than 800MBq (±10%),6,7 and b) the dose rate should be less than 40μSv/h at a distance of one meter away from the patient.7 Unless the above is achieved, to comply with the radiation limits to family members and the public, hospitalisation of patients is necessary.

For social and cultural reasons in Oman, thyrotoxic patients treated with ¹³¹I were hospitalised until their radiation level dropped to 2μSv/h at a distance of one meter corresponding to body retained activity of less than 30MBq as advised by UK guidance notes.8 Using a similar body retention of ¹³¹I activity, a study performed by Bererhi and Constable9 in 2000, found that doses received by family members of treated thyrotoxic patients were within allowed limits. Subsequently, a significant shortening of hospitalisation stays of these patients was implemented in Oman.

The advantage of treating these patients as outpatients is that it reduces the burden on the health care systems including treatment expense and waiting list length, with the added benefit of patient comfort and satisfaction. This study was conducted as a follow up study to that of Bererhi and Constable9 to test thyrotoxic patients as outpatients after radioiodine therapy.

Methods

Eighty-six family members of 22 self-dependent thyrotoxic patients, treated with ¹³¹I as outpatients, participated in this study which was conducted between February 2007 and March 2008. All patients agreed to participate in this study. Patients and family members were monitored for radiation exposure for 10 days using thermoluminescent dosimeters (TLDs). This period was selected as the highest radiation exposure falls within these days. The mean age of the family members was 26.6 years (range 17 months - 75 years) and included 29 children ≤ 16 yrs and 57 adults (11 spouses and 8 parents). Radiation dose rates at one meter from patients were measured following the administration of ¹³¹I using a portable calibrated dose rate meter (type PDR1).

Written and verbal local radiation safety instructions [Table 1] were provided to all patients prior to discharge. Patients and their accompanying relatives wore their dosimeters before leaving the hospital. On their journey back home, patients were advised to sit in the back of the car on the opposite side from the driver to keep the distance between them at a maximum.

Table 1:

Local radiation safety instructions for 131I therapy outpatients

1. Avoid all close contact with children and pregnant women for three weeks

2. Avoid prolonged personal contact with adults for two weeks

3. Do not sleep with an adult/child on the same bed for three weeks

4. You may return to work after..........days (depending on occupation)

The selection criteria were based on the following: a) patient and family members had to consent to wearing the dosimeter at all times for 10 days starting from the day the patient returned home; b) patient and family members had to live together in the same house during the whole period the dosimeter was worn. Some patients were called randomly to confirm that they were fulfilling the above criteria.

Thermoluminescent dosimeters (TLD), TLD 200 rods, (6mm x 1mm diameter) made of CaF₂:Dy were used in this study. A Harshow 5500 TLD reader was used to read the TLDs [Figure 1]. The rods were carefully handled with a vacuum tweezer and stored on a numbered plate in order to keep track of the individual dosimeters. The dosimeters were annealed at 320°C for 1 min. in a TLD-Oven to clear them from any residual absorbed doses. For individual TLD calibration, all TLDs were irradiated to a dose of 1.0mGy using a ⁹⁰Sr Irridiator 2000. From the resultant TLD readings, the mean reading was calculated. The ratio of the individual and mean reading was taken to represent a calibration factor known as element correction coefficient (ECC) to compensate for variations in geometry and sensitivity among dosimeters. The reader was calibrated to produce consistent and accurate readings in dosimetrically meaningful units (μGy) by applying a reader calibration factor (RCF).10

Figure 1:

Harshaw 5500 thermoluminescent dosimeter reader

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 watertight painted capsule, with a screw-in end piece, and a cord was threaded into two holes at the extremities of the capsule, designed in such a way that, once the cord was in place, the capsule could not be opened. The lengths of the cord were adjusted to bring the capsule to the level of the supra-sternal notch [Figure 2]. The capsules were placed in individually labelled lead pots, which were then fitted into a wooden box [Figure 3] together with a dosimeter for background measurement. The patients were asked to keep the background dosimeter in a place remote from general living activities. After the TLDs were returned, they were preheated in the TLD oven at 100°C for 20 minutes then read out in the TLD reader using a time-temperature profile of 200°C for 100s, 400°C for 300s and 400°C for 200s for preheating, acquisition and annealing, respectively. The average doses from the three TLD rods of each member were recorded after background subtraction.

Figure 2:

Dosimeter positioned at level of suprasternal notch

Figure 3:

Set of dosimeters in lead pots within wooden box for patients and family members

Results

In compliance with the European Commission (EC) guidelines7 regarding radioiodine therapy patient discharge, our patients left the hospital with mean (±SD) administered doses of 609.8 ±79MBq in the range 520–862MBq and mean radiation exposure dose levels of 23.4 ±6.3μSv/h in the range 13 to 42μSv/h. at one meter from the patient. The cumulative radiation doses (μSv) over 10 days received by the family members are shown in Table 2. All family members, including spouses, received less than the annual dose limit of 1mSv except for four out of 29 children (14%), aged 19 months and 12, 13, 15 years, who received radiation doses of 2.9, 1.2, 1.2 and 1.2 mSv, respectively [Figure 4]. The 19 month-old infant’s mother was treated with 555MBq of ¹³¹I and her radiation level at one meter, when leaving the hospital, was 13μSv/h. The 12 and 15 year old children were the younger sisters of a patient who was treated with 585MBq of ¹³¹I and her radiation level at one meter, when leaving the hospital, was 26μSv/h. The 13 year old child’s mother was treated with 566MBq of ¹³¹I and her radiation level at one meter, when leaving the hospital, was 19μSv/h.

Table 2:

Cumulative radiation doses over 10 days received by relatives of Omani thyrotoxic out-patients treated with 131I with a mean of 609.8 ±79MBq

Relatives	No.	Radiation Dose (μSv)
		Min	Max	Mean	SD
Spouses	11	7	425	105	152
Others	75	0	2921 (child)	206	440

Figure 4:

Dot-plot showing the radiation doses received by family members in reference to annual dose limit. The mean radiation dose is shown in dotted line

Discussion

Although the release criteria limit in this study were less stringent than the recommended limits in some developing countries, where literacy and socio-economical factors were taken into account, such as in India (patient retained activity at discharge ≤ 600 MBq, or dose rate level of 30 μSv/hr at 1 meter from patient)11 and Pakistan (patient retained activity at discharge < 370 MBq, or dose rate level of ∼ 10 μSv/h. at 1 meter from patient),12 95% of family members in this study received radiation dose levels lower than the annual limit of 1mSv [Figure 4]. This proves that the radiation safety instructions given and explained to patients and family members were understood and taken seriously by both patients and family members. The remaining family members who received doses higher than the annual radiation dose limit were children. These doses were received due to socioeconomic conditions, i.e. children belonged to homes where they were no person other than the mother to take care of them. This is seen in the case of the 19 month old child who was looked after only by the mother and slept with her in the same bed, although clear radiation safety instructions were given to the mother strictly to avoid contact with her child. However, it is common practice in Oman that mothers sleep with their infants in the same room and children are very much attached to their parents, making the situation difficult to avoid. Living conditions of some families, i.e. number of rooms in the house, was a factor that caused high radiation exposure to the other three children. The 23 year old patient lived in a house with only two rooms and slept with four other family members in the same bedroom exposing her younger sisters aged 12 and 15 years-old to a radiation dose higher than the annual dose limit. The 13 year old girl lived in a house with three rooms and slept in the same bedroom with her mother who received the therapy.

The mean cumulative radiation doses received by spouses of this study was lower than the mean cumulative radiation doses received by spouses in Bererhi and Constable’s9 study in 2000. These results were obtained taking into account that the retained mean body activity in our patients when leaving the hospital was about 20 times (609.8 versus 30MBq) more than that reported by Bererhi and Constable9, and the time the dosimeters were worn in our study was longer than in Bererhi and Constable’s study9 (10 days versus 7 days). Our outpatients were also strictly advised to sleep separately from their spouses for a period of three weeks post-therapy whereas spouses in Bererhi and Constable’s study slept in the same bed. In the study by Monsieurs et al.,13 recommendations for spouses of thyrotoxic patients treated with radioiodine was to sleep separately for a duration of 21 days in order to comply with the annual dose limit of 1mSv. In our study, using the same instructions, the same results were achieved indicating good compliance with the radiation safety instructions given.

Conclusion

In our institution, thyrotoxic patients treated with radioiodine are hospitalised for a few days. The results of this study show that with good radiation safety instructions to patients and relatives, thyrotoxic patients may be treated as outpatients provided the patient is physically and mentally fit enough to comply with the given instructions. However, the decision of releasing these patients from the hospital should be based on several factors including travelling distance, socio-economic conditions and family life style.

We recommend that: 1) mothers with children below the age of 3 years should not be treated as outpatients unless arrangements can be made for their children to be looked after by someone else other than the mother for a few days as recommended elsewhere;14,15 2) patients sharing the same room with many other family members should be hospitalised for a few days to avoid unnecessary radiation exposure to others.