Estimation of radiation dose to commuters using patient transport from thyrotoxicosis patients treated with I-131 at universitas academic hospital

Abstract

The prevailing economic disparity causes patients from various parts of the Free State and Northern Cape Provinces in South Africa and Lesotho to be treated with radioactive I-131 for thyrotoxicosis at Universitas Academic Hospital. Some patients are obliged to travel long distances (4–9 h) using patient transport services after discharge, causing concern for public exposure of nearby passengers due to a public dose limit of 1 mSv year⁻¹. The study aimed to estimate the commuters’ radiation exposure from 62 thyrotoxicosis patients post-treatment with I-131. An electronic personal dosimeter and ionisation chamber survey meter were used to measure radiation exposure in the isolation room and from the I-131 patients. The results showed that the radiation dose in the room had a mean of 387 ± 185 µSv for 18.6 ± 6.9 h. Furthermore, the exposure rate with a survey meter at 0.3 m had a mean of 217.2 ± 45.8 µSv h⁻¹ and a mean of 25.4 ± 5.4 µSv h⁻¹ at 1 m from the patients. The dose to passengers in patient transport could be higher if patients were treated as outpatients and adhering to the release criteria of 25 µSv h⁻¹ or 555 MBq limit without considering the socioeconomic factors of the patients.

1. INTRODUCTION

The treatment of thyrotoxicosis with radioiodine (I-131) has been established as one of the primary methods of regulating thyroid disease (Franklyn and Boelaert, 2012). Radioiodine treatment is cost-effective as many patients can be treated as outpatients without complicated intervention in countries where the disease burden has increased, placing strain on tertiary hospitals. However, radioiodine has radiation protection issues against other nearby individuals, as shown in the literature, for example, in a study by Barrington et al. (1999). The treatment requires restrictions by regulators to reduce the radiation dose to as low as reasonably achievable for the individual (Stefanoyiannis et al., 2015). One path to providing equitable quality health care is centralising tertiary hospital services due to staff and resource constraints (Slabbert and Smith, 2011). The centralisation of tertiary hospitals means that patients from rural districts and regional hospitals must travel to tertiary hospitals where nuclear medicine departments are located. In South Africa (SA), the Department of Health in the Free State (FS) Province and other provinces have implemented daily non-emergency patient transport to transfer patients to and from tertiary hospitals (Mahon, 2011). Compounding the problem of patient transportation is that the country's provinces are enormous, and, in some instances, the distances between towns in the province and Bloemfontein (BFN), where the treatment centre is located, are vast, as shown in Fig. 1.

Fig. 1.

(A) A map showing the Free State Province where the metropole of Bloemfontein is situated and (B) a sample of four towns indicated on the map with their respective distances from Bloemfontein to where Universitas Academic Hospital is situated.

Thyrotoxicosis patients from various parts of the FS and Northern Cape (NC) Provinces in the Republic of South Africa and the Kingdom of Lesotho (Fig. 1) are treated with radioactive I-131 at Universitas Academic Hospital (UAH) in BFN, FS, to control the disease. The South African Health Product Regulatory Authority (SAHPRA) conditions and guidelines state that a patient must be accommodated in a single room if the activity exceeds 555 MBq or the exposure rate exceeds 25 µSv h⁻¹ (SAHPRA, 2022). The challenge comes after the I-131 treatment, when the patients must return to their homes. Our previous literature review (Mongane and Rae, 2017) recommended that patients’ socioeconomic factors be considered at the onset of hospital admission. Due to prevailing economic disparity, some patients may thus be obliged to travel long distances (4–9 h), as shown in Fig. 1 in patient transport services (Fig. 2) after discharge, causing concern for public exposure due to a public dose limit of 1 mSv year (ICRP, 1990). The distance between the midpoints of two adjacent seats in a patient transport services vehicle is approximately 60 cm, meaning that most patients will sit near one another. This study used the electronic personal alarm dosimeter and ionisation chamber survey meter to measure the dose in the isolation room and the exposure rate from the I-131 patient to estimate the dose received by the nursing staff and commuters.

Fig. 2.

(A) The vehicle used for non-emergency patient transport and (B) the inside of the patient transport with adjacent seats close to each other as indicated by arrows.

2. MATERIALS AND METHODS

2.1. Electronic personal dosimeter (EPD)

Electronic personal dosimeters (Fig. 3A and B) were used to measure ambient dose rates in the isolation room of admitted I-131 patients. The number of patients occupying isolation rooms monitored between January 2023 and October 2023 was 45 (Fig. 4A). The EPD was fixed (Fig. 3C) at the wall on the head side of the patient's bed, approximately 1.5 m above the floor and 0.5 m from the patient's head when lying on the bed. The patient was free to move around the room and use a seat that was approximately 1.5 m away from the EPD. The average time to monitor the room's radiation levels was approximately 18.3 ± 2.1 h—the mean prescribed I-131 activity was 566.1 ± 103.6 MBq (15.3 ± 2.8 mCi).

Fig. 3.

(A) Isotrak EPD, (B) RadTarge EPD, (C) EPD setup, and (D) ionisation chamber survey meter (Victoreen).

Fig. 4.

Distribution of activities administered to patients: (A) room measurements and (B) exposure rate measurements.

2.2. Ionisation chamber survey meter

The exposure rate of 62 patients’ distribution is shown in Fig. 4B (January–October 2023) and was measured with an ionisation chamber survey meter (Fig. 3D) at 0.3 and 1.0 m from the patient, as described by Liu et al. (2015). The measurements were performed immediately after administration, and 1 day later, and the highest exposure rate from a patient was recorded.

3. RESULTS AND DISCUSSIONS

The results showed that radiation dose in the room varied from 153 to 799 µSv (median, 311.4 µSv; mean, 387.6 ± 185.2 µSv) for 18.6 ± 6.9 h post I-131 administration. The results in this study are lower than those in the study by Kocovska et al. (2011). They found an average of 870 µSv for family members staying with the patients for 10 days. The average dose measured for various activities is shown in Table 1, which gives insight into the doses around patients treated with I-131 for 1 day. In general, all the doses were below the 1 mSv limit, indicating that the distance between the EPD and the patient reduced the dose significantly. The implication is that increased distance between the passengers and I-131 patients in a patient transport vehicle can reduce the radiation dose even when traveling a long distance.

Table 1.

Electronic personal dosimeters exposure results for room measurements from the I-131 patients for various activities.

Activity (MBq)	Room exposure (µSv)
370	586.0 ± 302
444	382.7 ± 150
555	354.9 ± 171
740	429.5 ± 257

The results for the second part showed that the exposure rate with a survey meter at 0.3 m (median, 163 µSv h⁻¹; mean, 167.7 ± 43.1 µSv h⁻¹) and 1 m from the patient (median, 27.0 µSv h⁻¹; mean, 28.1 ± 7.6 µSv h⁻¹) immediately post I-131 administration was higher than the mean 110 µSv h⁻¹ at 0.3 m and 22 µSv h⁻¹ reported by Liu et al. (2015) for the average activity of 566 MBq. This study's results were also higher than the 13 ± 5 µSv h⁻¹ reported by Kadhim et al. (2020) at 1 m. The differences in the dose rates might be due to average activities and the biodistribution of I-131 in the populations studied. The results indicated that the I-131 patients might give significantly higher radiation doses to other passengers using patient transport due to the reduced distance between them. The exposure rates at 0.3 m for patients 24 h postinjection averaged 217.2 µSv h⁻¹, as shown in Table 2, which can easily exceed the 1 mSv public dose limit (due to the long distances indicated in Fig. 1) as most patients use the patient transport service to go home.

Table 2.

Survey meter results for exposure measure from the I-131 patients at two distances.

Time (hours) postinjection	Distance: 0.3 m	Distance: 1 m
0	167.6 ± 43.0 µSv h−1	28.1 ± 7.6 µSv h−1
24	217.2 ± 45.8 µSv h−1	25.4 ± 5.4 µSv h−1

4. CONCLUSION

The SAHPRA regulation of isolating patients after the I-131 therapy capsule ensures that the caregivers, family pets, family members, and the public are safe from radiation exposure by minimising the collective dose and the risk from ionising radiation. However, the dose to passengers in patient transport could be higher if treated patients were released based on adhering to the 25 µSv or 555 MBq limit without considering the socioeconomic factors of these patients.