METHODS
A total of 303 patients undergoing 131 therapies were recruited in this study. Dose rate measurements
were performed 22?24 h after radioiodine uptake. The patients with a dose rate <30 µSv/h were discharged.
Whereas, those with a 30?40 ?Sv/h dose rate were asked to drink further 1.5-2 liters of water
for 4-6 h. Then, post-voiding dose rate measurements were repeated.
RESULTS
Consequently, the patients administered with 1111?2775 MBq (30-75 mCi) were discharged after 24 h.
Among the patients treated with 3700 MBq (100 mCi), 21/29 patients (72.4%) had a dose rate between
30 and 40 ?Sv/h and they were released within 4-6 h after drinking 1.5?2.0 liters of water. For the patients
treated with 5555 MBq (150 mCi), 23/32 patients (71.8%) whose dose rate between 30 and 40
µSv/h were similarly discharged after drinking extra 1.5?2.0 liters of water within 4?6 h. Moreover, the
patients who were subjected to 7400?11100 MBq (200?300 mCi) 131I therapy were not asked to drink
extra water as the dose rates measured at the end of 24 h were >40 ?Sv/h and they were discharged later.
CONCLUSION
Consequently, it was manifested that around 72% of thyroid cancer patients who underwent radioiodine
therapy had a dose rate level 30?40 ?Sv/h after 24 h and could be discharged early by drinking 1.5-2.0
liters of water within 4-6 h.
Keywords: Dose rate; hydration; isolation time; radioiodine therapy; thyroid cancer
The emitted beta particles (606 keV) from radioactive
decays are used for therapy purposes, while the
emanated gamma rays are used for diagnostic scintigraphy.
In 2015, the American Thyroid Association (ATA) reported that for low-risk patients, it is recommended
to monitor the patient at certain intervals and
to administer a low dose of 1110-1850 MBq (30-50
mCi) 131I with respect to the clinician's opinion. Furthermore,
a fixed dose of 3700-5550 MBq (100-150
mCi) can be applied for medium-risk groups and
5550-9250 MBq (150-250 mCi) for patients with high
risk.[
The ATA criteria also recommended that the amount
of radioiodine activity to administer can be determined
by personalized dosimetry. In a study conducted by
Hindorf et al.,[
On the other side, in accordance with the legislation
in Türkiye, the radiation level on the patients should decrease
to 600 MBq activity or the dose rate measured at
1 m distance from the patient"s abdomen should be <30
µSv/h for patients" discharge. In daily practice, patients
whose dose rate is above the determined limit should
be hospitalized longer in the leaded isolation rooms.[7]
Before the treatment, radiation protection training
is given to the patients. During this training, it is recommended
to drink plenty of water 2 h after radioiodine
intake. This process is presented as a suggestion,
but cannot be followed.
This study aims to evaluate the dose rates measured
after receiving radioiodine therapy besides determining
the rate of radioiodine removal from the body in
patients whose dose rate is close to the discharging
dose limit after drinking plenty of water.
The dose rates (µSv/hour) of the hospitalized patients after 131I therapy were analyzed retrospectively.
The dose rate readings were measured with a Geiger- Müller radiation detector (Ludlum brand, 9DP model) at a distance of 1m from the abdomen. Dose rate levels for the hospitalized patients are routinely measured at 1 day, 2 days, and 3 days after radioiodine administration. The patients with a dose rate less than 30 ?Sv/ hr were promptly discharged. However, the patients who exhibited 30-40 µSv/h were hydrated by drinking 1.5?2 liters of water for 4-6 h. Then, the bladders were emptied and the measurements were repeated. Accordingly, the patients who showed a dose rate <30 µSv/hr in the second measurement were discharged.
The patients who received 131 treatments were divided into eight groups according to the administered activity as follows; 1111 MBq (30 mCi), 1850 MBq (50 mCi), 2775 MBq (75 mCi), 3700 MBq (100 mCi), 5555 MBq (150 mCi), 7400 MBq (200 mCi), 9250 MBq (250 mCi), and 11100 MBq (300 mCi).
The creatinine and urea values of the patients to be treated in the radioiodine treatment unit are checked. Patients with significant creatinine elevation are not treated.
DTC: Differentiated thyroid cancer.
Creatinine values were found to be 0.87±0.14 mg/dl, 0.89±0.21 mg/dL, 0.78±0.16 mg/dl, 0.90±0.14 mg/dl, and 0.78±0.28 mg/dL in those administered 3700 MBq (100 mCi), 5550 MBq(150 mCi), 7400 MBq (200 mCi), 9250 MBq (250 mCi and 11110MBq (300 mCi), respectively.
Of the treated patients, 181/303 (60%), 92/303 (30%), and 29/303 (10%) had findings of ablation therapy, ablation+lymph node metastasis, and distant metastasis, respectively. The mean TSH measurement values of all patients before treatment were 93 µLU/ml.
After 24 h, all of the patients (seven patients) who were rated with 1111 MBq (30 mCi) 131I were discharged with a mean dose rate of 10.2 µSv/h. 41 patients were treated with 1850 MBq (50 mCi) and discharged with an average dose rate of 15.4 µSv/h. Likewise, seven patients were treated with 2775 MBq (75 mCi) 131I and discharged after 24 h with an average dose rate of 15.1 µSv/h.
98 (77%) out of 127 patients were treated with 3700 MBq (100 mCi) 131I and the mean dose rate was mea sured as 22 µSv/h after 24 h. The dose rates of the remaining 29 patients were registered in a range of 30-40 ?Sv/hr (mean 36.8 µSv/h). These patients were asked to drink a further 1.5-2 liters of water for 4-6 h. The dose rate of 21 out of 29 patients declined to 23.6 µSv/h and so the patients were discharged 28-30 h after the administration. However, the dose rate of the remaining eight patients was >30 µSv/h and they were discharged in the next day with an average dose rate of 18.1 µSv/h.
In 20 (21.7%) of 92 patients treated with 5555 MBq (150 mCi) 131I, the mean dose rate was 21.2 µSv/h after 24 h and the patients were discharged. While the dose rates from the remaining 72 patients were found to be in the range of 30-40 µSv/h (mean 35.2 µSv/h) after 24 h. These patients were likewise asked to drink 1.5-2 liters of water for 4-6 h. Then, the dose rates were measured again showing 25.3 µSv/h in 23 out of 32 patients. Despite drinking plenty of water in 9 patients, the dose rate was >30 µSv/h and those patients were confined for additional day until the dose rate declined to 12.1 µSv/h.
Similarly in 2 (10.5%) of 19 patients treated with
7400 MBq (200 mCi) 131I, the mean dose rate was measured
as 26.2 µSv/h after 24 h and the patients were discharged.
However, the mean dose rate of the 17 patients
(89.4%) was measured at >30 µSv/h with an average of
75.2 µSv/h. Of these 17 patients, 12 were discharged
after 48 h with a mean dose rate of 16.6 and the rest
five patients were discharged in the 3rd day with a mean
dose rate of 22 µSv/h as the dose rates measured at the
24th and 48th h were >30 µSv/h. In 1 (1%) of 9 patients
treated with 9250 MBq (250 mCi) 131I, the mean dose
rate was measured as 23.2 µSv/h after 24 h. Whereas, the
dose rates of eight patients (88.8%) after 24 h were >30
µSv/h (mean 83.6 µSv/hr). Seven out of eight patients
were discharged after 48 h with a mean dose rate of 19.7.
The discharging time for the last one patient was postponed to the 3rd day with a dose rate of 3 Sv/h. Finally,
there was 1 patient who received 11100 MBq (300 mCi)
131I and the dose rates were found to be 145 µSv/h on
the 1st day and 29.5 µSv/h on the 2nd day (Table
Iodine-retaining metastases in the body also play a role in radioiodine biokinetics. In our study, 3/29 (10%) patients who were treated for distant metastases were discharged after 24 h. However, 20/29 (69%) patients in this group could be discharged after 48 h, and 6/29 (21%) patients could be discharged after 72 h despite hydration.
Conflict of Interest: All authors declared no conflict of interest.
Ethics Committee Approval: The study was approved by the Istanbul University-Cerrahpasa, Cerrahpasa Faculty of Medicine Ethics Committee (no: 32, date: 22/02/2022).
Financial Support: None declared.
Authorship contributions: Concept - N.İ.I., M.D., M.A.; Design - N.İ.I., M.D., M.A.; Supervision - N.İ.I., M.D., M.A.; Funding - N.İ.I., M.D., M.A.; Materials - None; Data collection and/or processing - N.İ.I., M.D., M.A.; Data analysis and/ or interpretation - N.İ.I., M.D., M.A.; Literature search ? N.İ.I., M.D., M.A.; Writing - N.İ.I.; Critical review - N.İ.I., M.D., M.A.
