Download Low Iodine Diet for One Week Is Sufficient for Adequate Preparation

THYROID RADIOLOGY AND NUCLEAR MEDICINE
THYROID
Volume 24, Number 8, 2014
ª Mary Ann Liebert, Inc.
DOI: 10.1089/thy.2013.0695
Low Iodine Diet for One Week Is Sufficient for Adequate
Preparation of High Dose Radioactive Iodine Ablation
Therapy of Differentiated Thyroid Cancer Patients
in Iodine-Rich Areas
Minkyung Lee,1 Yu Kyung Lee,1 Tae Joo Jeon,1 Hang Seok Chang,2 Bup-Woo Kim,2
Yong Sang Lee,2 Cheong Soo Park,2 and Young Hoon Ryu1
Background: Most current guidelines suggest one or two weeks of low iodine diet (LID) before radioactive
iodine ablation therapy (RAIT) to increase its efficacy in differentiated thyroid cancer (DTC) patients after total
thyroidectomy. LID duration is particularly important for patients living in iodine excess areas. However, there
is no standardized LID protocol and there are limited reports regarding the relationship between LID and
ablation outcome. Therefore, we aimed to evaluate the optimal LID duration and define clinical features that
affect ablation outcome.
Methods: A total of 202 papillary thyroid cancer patients with total thyroidectomy preparing for RAIT were
enrolled. All patients had undergone two weeks of LID before 131I administration. Morning spot urine specimens were obtained twice (one week or two weeks after LID, respectively) from each patient. Urine iodine
excretion (UIE) values were used to evaluate LID efficacy. Successful ablation was defined using two definitions: (i) no visible uptake on a follow-up diagnostic 131I scans, and (ii) no visible uptake on a follow-up
diagnostic 131I scans and stimulated serum thyroglobulin (Tg) levels <1 ng/mL.
Results: The UIE median values after LID for one and two weeks were lower than 50 lg/L, and the median UIE
values were not significantly different according to the LID duration. Based on the first criterion for successful
ablation, 175 of the 195 patients were successfully ablated. There were no significant differences in mean and
median UIE levels between the ablated and non-ablated groups after LID for two weeks. The rate of ablation
did not differ between the mild and moderate iodine deficient groups. Based on the second criterion for
successful ablation, 149 of 188 patients were successfully ablated. The ablation success rate did not differ
between UIE levels. When we analyzed clinical factors that affect ablation outcome, serum Tg level at the time
of ablation was the only significant variable in multivariate logistic analysis.
Conclusion: Strict LID for one week was sufficient to achieve target UIE values for RAIT preparation, even in
iodine-rich areas.
Introduction
adioactive iodine (131I) provides therapeutic effects in
differentiated thyroid cancer (DTC) by its beta-emission
and also emits gamma rays that can be detected by gamma
cameras (1). Because of these characteristics, 131I has been
widely used for therapeutic purposes and monitoring of recurrent or metastatic DTC.
Delivery of optimal radiation doses to the thyroid remnant
or tumor is an important factor for successful radioactive
R
iodine therapy (RAIT) (2,3). There are two main approaches
to increase ablation efficacy. The first approach is increasing
serum thyroid stimulating hormone (TSH) concentrations
(4), whereas the second is depletion of the whole-body iodine
pool (3). The former is achieved by thyroid hormone withdrawal or recombinant human TSH (rhTSH) injection (1).
Withdrawal of thyroid hormone prior to RAIT is the more
traditional and typical method, but it causes patients to suffer
from hypothyroidism symptoms (5). The latter is obtained by
restriction of daily iodine intake thorough a low iodine diet
1
Department of Nuclear Medicine and 2Department of Surgery, Thyroid Cancer Center, Gangnam Severance Hospital, Yonsei College of
Medicine, Seoul, Korea.
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1290
(LID) before RAIT (6,7). Most guidelines recommend limiting dietary iodine intake to 50 lg daily for one to two weeks,
but there are still no standardized LID protocols (8–10).
Evaluation of the body iodine pool using urine analysis is
recommended before RAIT because urine iodine excretion
reflects very recent dietary iodine intake well (11,12). Previous reports have demonstrated that morning spot urine
analysis can be an alternative method to 24-hour urine sampling for assessment of iodine nutrition status (13–15). The
European Association of Nuclear Medicine (EANM) Therapy Committee in 2008 proposed to defer RAIT in patients
with DTC when the random urinary iodine concentration is
above 150–200 lg/L (16).
The stringency and duration of LID for achieving adequate
iodine depletion before RAIT may vary due to geographic
differences in dietary iodine intake (17–19). For example,
Korea is bound by the sea on three sides, and the dietary
iodine intake level from seafood is higher compared with all
other countries except Canada and Japan (18–20). A strict
LID for two weeks is often recommended in Korean clinics
due to the common belief that a longer LID period is necessary to achieve sufficient iodine depletion in this iodine
excess area. However, the optimal LID duration is still debatable and a two-week LID may be too long for the patient to
tolerate, decreasing their quality of life quality compared to
other countries. The disadvantage is due to the Korean patients’ greater reliance on an iodine-heavy diet. While the
period of LID may be the same, a Korean patient has to make
a greater change to restrict his or her diet. For instance, salted,
fermented food prepared with iodized salt—including kimchi, red pepper paste, pickled seaweed or fish, and soybean
paste—are essential to Korean cuisine. Many Koreans just
cannot have a meal without it and these foods are hard to
avoid. However, the low-iodine guidelines prohibit intake.
The maintenance of LID, therefore, can be a more difficult
task for Koreans than patients in other countries. In our experience, a LID could be a source of anxiety because the
patients feel that the variety of foods that could be eaten
safely is low. It can cause significant dietary disruption and
restriction of patients’ social life. Based on these considerations, we aimed to evaluate the optimal duration of LID
required to reach an adequate body iodine pool level before
RAIT administration for patients in iodine rich areas. We also
examined the relationship between body iodine pool levels
and ablation efficacy using spot urine analyses.
Materials and Methods
Patients
Patients (n = 202) preparing for RAIT after total thyroidectomy due to papillary thyroid cancer were enrolled between April 2012 and July 2013 at the Thyroid Cancer Center
at Gangnam Severance Hospital. They were referred for the
purpose of thyroid remnant or metastasis ablation after surgery and no grossly visible thyroid remnants remained in any
cases. Applied 131I doses were determined depending on
the initial cancer extension (range, 3.70–7.40 GBq) using the
tumor, lymph node, metastasis classification system of the
American Joint Committee on Cancer classification. For
postoperative ablation of thyroid bed remnants, 3.7 GBq of
131
I was administered. Activities in the range of 4.81–5.55
GBq were typically administered for treatment of presumed
LEE ET AL.
thyroid cancer with central neck node metastasis. In cases of
thyroid cancer with lateral neck or mediastinal node metastasis, activities in the range of 6.66–7.40 GBq were given.
Patients who did not wish to participate in the study were
excluded. Additionally, patients with a history of chronic
renal disease or patients who could not follow instructions
due to his/her psychiatric disability were also excluded. Posttherapy 131I-whole body scintigraphy (WBS) was performed
9 to 10 months after ablation using a dual-head gamma
camera (Symbia E; Siemens Medical Solutions, Malvern,
PA) equipped with parallel-hole, medium energy collimators
and 364 keV energy peak with a 15% window and an acquisition time of 20 min/projection. Anterior and posterior
projection images were obtained. According to the ablation
and follow-up protocols, all patients were withdrawn from
levothyroxine four weeks prior to RAIT and WBS, which
was replaced with liothyronine for two weeks followed by
withdrawal of T3 for 2 weeks (thyroid hormone withdrawal,
THW). Patients completed a specific LID for two weeks
before 131I administration. Prior to starting LID, they were
educated by specially trained nurses who provided information about drugs and foods that are allowed or not during
the LID period. The patients were also given a dietary
guide (Table 1) and sample LID menus to take home. The
Gangnam Severance Hospital Review Board approved the
study design, and written informed consent was obtained
from all patients.
Laboratory data analyses
Morning spot urine specimens were obtained twice from
each patient and the urine iodine excretion (UIE) was obtained
Table 1. Low-Iodine Diet Guidelines
Not allowed
Sea salt/iodized salt
Milk or other dairy products
Seafood including fishes,
seaweeds, and shellfish
Food or drugs containing
red color food dye
Salted-fermented food
made with iodized salt,
including kimchi, red
pepper paste, and soybean
paste.
Snacks and nuts made
with iodized salt
Restaurant food
Cured and canned foods
including ham,
corned beef,
canned fish,
and canned fruits
Multivitamins
Allowed
Non-iodized salt
Fresh fruits and
vegetables
Mushrooms
Egg whites
Meat including beef,
pork, and chicken
Black coffee, tea,
and isotonic drinks
Nuts
Rice, wheat flour,
and mixed grains
Condiments including
sugar, garlic, black
pepper, red pepper
powder, vinegar,
ginger, mustard,
wasabi, herb, sesame,
and vegetable oil
LOW IODINE DIET FOR PREPARATION OF
131
I ABLATION THERAPY
to evaluate LID efficacy. The first urine sample was taken
one week after starting LID and the second one was taken
two weeks after the LID protocol. Urine iodine was measured using inductively coupled plasma mass spectrometry
and an Agilent 7500 series instrument (Agilent Technologies, Inc., Tokyo, Japan). The reference range was 23.9–
4322.8 lg/L.
Urine iodine depletion was categorized based upon previous reports and World Health Organization (WHO) criteria
for assessing iodine nutrition status: median urinary iodine
concentrations of ‡100 lg/L define a population that has no
iodine deficiency. UIE concentrations <50 lg/L were considered moderately iodine deficient, whereas levels ‡50 ll/L
but <100 lg/L correspond to mild iodine deficiency (15).
These two criteria are regarded as adequate LID preparation
for RAIT administration. The cutoff value of UIE, which
indicates poor LID preparation, was ‡100 ll/L. Seven patients with poor compliance (the patients did not follow the
LID recommendations) were excluded from the analyses.
Poor compliance was defined as (i) UIE levels greater than
the mean UIE values of normal Korean patients (478.6 lg/
day) (20) in both the first and second week LID, and (ii)
patients who achieved adequate UIE levels during the first
week LID but showed high UIE levels ( ‡50 ll/L) during the
second week LID.
Blood samples for serum TSH, stimulated thyroglobulin
(Tg), and thyroglobulin antibodies (TgAbs) were obtained on
the day of RAIT administration. Serum TSH levels were
analyzed using an immunoradiometric assay (TSH-CTK-3,
SORIN Biomedica, Saluggia, Italy), and the reference range
is 0.86–4.69 mU/L. 131I was administered when TSH levels
were >30 mU/L in all patients. Serum Tg was measured
using the Modular E170 (Roche Diagnostics, Mannheim,
Germany) with an analytic sensitivity of 0.1 ng/mL. Serum
TgAbs were detected using an immunoradiometric assay (Tg
plus RIA; Brahms AG, Hennigsdorf, Germany) and values
below 124.2 U/mL were considered negative.
Ablation success criteria
To evaluate the RAIT success rate, we used two criteria for
successful thyroid ablation. The first criterion was no visible
neck uptake in the diagnostic WBS. The second criterion was
no significant neck uptake on a diagnostic WBS plus undetectable serum Tg levels (<1 ng/mL) after TSH stimulation in
the absence of circulating TgAbs. Radioiodine WBS was
visually interpreted by two experienced nuclear physicians to
obtain consensus readings. The results are classified as positive or negative according to whether there was uptake in
the neck.
Statistical analyses
Statistical analyses were performed using SPSS 18.0 statistical software for Windows (SPSS Inc., Chicago, IL).
Numeric data are expressed as the mean – standard deviation.
Wilcoxon signed-rank tests, Mann-Whitney U tests, McNemar’s tests, and chi-square tests were used to assess statistical
differences between groups. Multivariate logistic regression
analysis was used to find the association between variables
with ablation success. A p-value <0.05 was considered statistically significant.
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Results
Patient characteristics
A total of 195 papillary thyroid cancer patients (149
females, 46 males) were enrolled. Their mean age was
44 – 11.08 years (range 22–73 years). Among the enrolled
patients, 74.9% had lymph node metastasis at the initial
presentation, and TSH levels were greater than 30 mU/L in all
patients. The mean sTg level was 7.63 – 18.66 ng/mL (median 2.7 ng/mL, range 1–179.2 ng/mL) in patients with negative TgAbs at the time of 131I administration. The patient
characteristics are summarized in Table 2.
LID efficacy
The median values of UIE after 1-week LID and 2-week
LID were 12.80 lg/L and 13.40 lg/L (Table 3). The median
UIE values were not significantly different ( p = 0.03, Wilcoxon signed-rank test) according to LID duration. UIE
levels lower than 50 lg/L were noted in 170 out of 195 patients (87.2%) after LID for 1 week and in 180 of 195 patients
(92.3%) after LID for 2 weeks. Mild iodine deficiency was
noted in 17 of 195 patients (8.7%) after LID for 1 week and in
15 of 195 patients (7.7%) after LID for 2 weeks. The frequencies of mild and moderate iodine deficiency did not
differ between 1-week and 2-week LID ( p = 0.06 and
p = 0.84, McNemar’s test). There were 8 patients (4.1%) with
Table 2. Baseline Patient Characteristics
All (n = 195)
Age (years)
Mean – SD
Median
Range
Sex, n (%)
Female
Male
TNM, n (%)
T1-3N0M0
T1-3N1M0
Dose of RAIT (GBq)
Mean – SD
Median
Range
Peak TSH (ablation) (mU/L)
Mean – SD
Median
Range
44 – 11.08
44
22–73
149 (76.40)
46 (23.60)
49 (25.10)
146 (74.90)
5.04 – 1.03
4.81
3.70–7.40
72.27 – 21.49
72.15
32.33–100
(n = 188)
Stimulated serum Tg at ablation in patients with TgAb( - )
Detectable ( ‡1 ng/mL), n (%)
101 (53.72)
Mean – SD
7.63 – 18.66
Median
2.7
Range
1–179.2
Undetectable ( <1 ng/mL), n (%)
87 (46.28)
Data are presented as the numerical value or the mean – standard
deviation (SD).
RAIT, radioactive iodine ablation therapy; Tg, thyroglobulin;
TgAb, thyroglobulin antibody; TNM, tumor, lymph node, metastasis classification system; TSH, thyroid stimulating hormone.
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LEE ET AL.
Table 3. Urinary Iodine Excretion (lg/L)
After LID Preparations for One or Two Weeks
All (n = 195)
Female
(n = 149)
Male
(n = 46)
One week
Mean – SD 28.20 – 28.96 27.20 – 28.84 31.42 – 29.40
Median
12.80
12.80
22.00
Two weeks
Mean – SD 22.62 – 15.48 23.03 – 16.09 21.31 – 13.39
Median
13.40
13.40
13.35
Data are presented as the numerical value or the mean – SD.
LID, low iodine diet.
UIE levels over 100 lg/L after LID for 1 week. The highest
UIE value in these patients was 148.5 lg/L. There were no
inadequately prepared patients after LID for 2 weeks.
Ablation outcomes based on the first criterion
and clinical features associated with successful ablation
weeks ( p = 0.40, Mann-Whitney test) (Fig. 1). Additionally,
we analyzed other possible variables that affect ablation
outcome, including age, sex, ablation dose, lymph node
metastasis, and TSH levels. However, we could not find any
significant clinical factors (Mann-Whitney and chi-square
tests). The rate of successful ablation did not differ between
the mild and moderately iodine deficient groups ( p = 0.36,
chi-square test) (Fig. 2A).
Ablation outcomes based on the second
criterion and clinical features associated
with successful ablation
Seven patients with positive TgAbs were excluded and a
total of 188 patients were enrolled in the analyses. Among
them, 149 patients (79.26%) were successfully ablated according to the second criterion. The ablation success rate did
not differ between the mild and moderately iodine deficient
groups ( p = 0.54, chi-square test) (Fig. 2B). Serum Tg levels
at the time of ablation therapy (ablation-Tg) were higher in
There were 175 patients (89.74%) patients classified as
successfully ablated based on the first criterion. There were
no significant differences in the mean and median UIE values
between the ablated and non-ablated groups after LID for 2
FIG. 1. Differences in mean and median urine iodine
excretion (UIE) (lg/L) values according to ablation outcome (based on criterion 1; negative whole body scintigraphy [WBS]). *Mean, **median.
FIG. 2. (A) Relationship between success rate and UIE
levels after two-week low iodine diet (LID2) of ablation
according to criterion 1 (negative WBS). (B) Relationship between success rate and UIE levels after LID2
according to criterion 2 (negative WBS and serum thyroglobulin <1 ng/mL).
LOW IODINE DIET FOR PREPARATION OF
131
I ABLATION THERAPY
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Table 4. Clinical Features Associated with Successful Ablation Based on the Second Criterion*
Age (years)
Sex, female, n (%)
Positive LN metastasis, n (%)
TSH at ablation (mU/L)
Mean – SD
Median (range)
Dose of RAIT (GBq)
Mean – SD
Median (range)
UIE values after two-week LID (lg/L)
Mean – SD
Median (range)
Tg level at ablation (ng/mL)
Mean – SD
Median (range)
Ablated
Non-ablated
p-Value
44.83 – 10.83
116 (77.90%)
108 (72.50%)
43.49 – 15.58
27 (69.20%)
32 (82.10%)
0.54
0.20
0.22
0.37
71.39 – 21.89
71.42
74.44 – 19.96
72.69
4.98 – 1.04
4.81 (3.70–6.67)
5.15 – 0.95
5.55 (3.70–7.40)
23.20 – 15.58
14.70 (12.80–85.40)
19.73 – 14.90
12.80 (12.80–88.90)
2.07 – 3.77
0.80
12.59 – 28.93
5.20
0.20
0.70
<0.001
*The second criterion for successful ablation is no visible uptake on a follow-up diagnostic 131I scan and stimulated serum thyroglobulin
(Tg) levels <1 ng/mL.
LN, lymph node; UIE, urine iodine excretion.
the non-ablated group compared with the ablated group, and
the differences were statistically significant ( p = 0.00, MannWhitney test). However, other factors, including age, sex,
administered radioactive iodine dose, UIE after LID for 2
weeks, and TSH levels, did not differ between the two groups
(Mann-Whitney and chi-square tests) (Table 4). The stimulated Tg level was the only significant variable ( p < 0.001) in
multivariate logistic analysis (Table 5).
Discussion
Iodine is accumulated in thyroid tissue via the sodium/
iodide symporter (NIS) (21). The NIS is a membrane protein
that actively transports iodide ions into thyroid tissue and
thus enables the high efficiency of radioiodine therapy (22).
Iodine excess can result in saturation of iodine uptake sites in
malignant and benign thyroid cells and cause decreased ablation efficacy. The study by Pluijmen et al. supported this
Table 5. Independent Factors Associated with
Ablation Outcome Based on the Second Criterion*
Multivariate logistic analysis
Age (years)
Sex (F/M)
Dose of RAIT (GBq)
LN metastasis
UIE after two-week
LID (lg/L)
Ablation-TSH (ng/mL)
Ablation-Tg (ng/mL)
p-Value
Odds
ratio
95% CI
0.47
0.49
0.37
0.34
0.18
0.99
0.73
1.01
0.54
1.01
0.95–1.03
0.30–1.77
0.99–1.03
0.15–1.92
0.10–1.03
0.63
< 0.001
1.00
0.85
0.98–1.02
0.79–0.91
*The second criterion for successful ablation is no visible uptake
on a follow-up diagnostic 131I scan and stimulated serum thyroglobulin (Tg) levels <1 ng/mL.
CI, confidence interval.
theory (23): the LID group achieved higher successful ablation rates compared to the control group in their study.
Goslings also reported that the effective half-life of radioactive iodine was increased after an 8-day LID (24). Similarly, Maruca et al. demonstrated that the lesional radiation
was increased in two patients with metastatic thyroid carcinomas after a 5-day LID (25). Furthermore, several previous
studies documented that NIS expression increased when the
plasma iodine concentration was low (4,26,27), which can be
an additional theoretical rationale for LID. Based on these
data, in many countries, patients preparing for 131I ablation
therapy are educated to avoid iodine-rich food and iodinecontaining medications during the LID period. However,
patients often complain of difficulties in maintaining a strict
LID for extended periods of time. Thus, attempts to reduce
the duration of a strict LID can be important in clinical situations, particularly iodine-rich countries.
The average iodine intake of normal Korean adults is
478.6 lg per day, and the average urine iodine concentration
in the random urine is 674 lg/g (20,28). Considering that
urinary iodine concentrations of 100 lg/L roughly correspond with a daily iodine intake of approximately 150 lg
(15), mean UIE levels after LID for 1 and 2 weeks in our
study were sufficiently low and both met the criteria for
iodine deficiency. Successful iodine depletion was accomplished in 95.9% (187/195) of patients after LID for 1 week
(87.2% of patients were moderately iodine deficient and
17% were mildly iodine deficient). Our results agree with
data from a previous report that was also performed in
Korea (29). These authors determined daily urinary iodine/
creatinine ratios (I/Cr) and founded that the I/Cr ratio decreased below the cutoff value for iodine deficiency on day
6 of LID.
Sawka et al. examined all published literature on the topic
of LID in 2010 (7). The authors reported that a LID does
reduce urinary iodine output and LID for 2 weeks is about
twice as effective as 1 week in their systematic review
(7,30,31). Head-to-head comparison between our study and
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reviewed studies is difficult to perform because there is variation in methodologies, stringency of the restriction, duration of LID, geographic differences in dietary iodine intake,
and disease-state of the subjects. Despite these limitations,
the rates of successful iodine depletion after LID for 1 and 2
weeks in our data set were higher and UIE levels were lower
than in previous reports (30–32). Park et al. reported that 41%
of patients obtained the targeted reduction of UIE (<100 lg/
gCr) after LID for 1 week (30). Another study performed in
Japan also found that 26% of patients achieved optimal UIE
levels (<100 lg/gCr) after LID for 1 week (31). These discrepancies are possibly due to the effects of intense patient
education and improved accessibility to medical staff. Previous reports provided a one-page sheet as an LID guide only
at the regular visit to the outpatient clinic. In contrast, our
hospital provides a 90-minute intensive LID education program to all patients by specially trained nurses and nutritionists. We have also established a hotline to answer patient
questions regarding LID. These efforts might increase patient
compliance with LID, resulting in higher LID success rates.
In our study, there were eight patients (8/195, 4.1%) classified as poorly prepared ( ‡100 ll/L, highest value: 148.5 lg/
L) after LID for 1 week. Although their UIE levels did not
satisfy WHO criteria for iodine deficiency (UIE levels
<100 lg/L) (15) they complied with the recommendation of
the EANM guidelines (UIE levels <150–200 lg/L) (16).
Furthermore, ablation success rates based on the first criterion were not significantly different between the mild (UIE
<50 lg/L) and moderatly iodine deficient (50 £ UIE < 100)
groups. A similar result was obtained based on the second
criterion. These data indicate that strict LID for 1 week is
enough to achieve appropriate decreases in the body iodine
pool before 131I ablation therapy, even in areas of iodine
excess. Therefore, in subjects with UIE levels below
100 lg/L, efforts to turn mild iodine deficiency into moderate iodine deficiency by maintaining a strict LID for
longer than 1 week will not increase the dietary efficacy of
LID or the rate of successful ablation. However, it will
increase patient inconvenience.
During long-term follow-up, serum Tg is a sensitive and
reliable tumor marker for detection of disease recurrence
and residual viable tumor after total thyroidectomy with or
without RAIT in patients with DTC. Recent studies proposed that measurement of ablation-Tg forecasts treatment
outcome. Lee et al. suggested that a post-operative stimulated Tg <2 ng/mL predicted disease-free status (33). Another study also suggested that ablation-Tg values correlate
well with serum Tg levels at the time of initial diagnostic
WBS and have a complementary role for predicting persistent or recurrent DTC (34). These results agree with our
present results. When we evaluated potential factors that
affect successful ablation, ablation-Tg in patients with
negative TgAbs was the only factor associated with ablation
success. This result suggests that patients who have small
volumes of potential Tg-expressing foci, including remnant
thyroid tissue or lymph nodes, tend to be easily ablated.
Therefore, it is not the body iodine pool level but rather the
ablation-Tg level that is a decisive factor to determine ablation outcomes when UIE levels enter into the target value
(<100 lg/L).
In our study, the administered dose of 131I was not a significant indicator of ablation success. This result has a limi-
LEE ET AL.
tation because it was not derived from the data on radiation
absorbed dose to the blood (BD). The mode of TSH stimulation (THW or rhTSH), renal clearance rate, and body iodine
concentration are possible factors that can impact radioactive iodine (RAI) kinetics (35). In a study by Verburg et al.,
the success of ablation increased with increasing BD, but no
dependence of the ablation rate on the administered activity
was demonstrable (36). This means that the BD is a more
powerful predictor of the successful ablation than the administered dose of 131I, considering the variation of iodine
kinetics in each individual. A direct comparison between our
results and theirs are difficult. However, the better successful
ablation rates of our study than those in the study by Verberg
et al. (89.74% vs. 76%, based on criterion 1 and 79.26% vs.
57%, according to criterion 2) may be partly related to the
difference in RAI kinetics. Therefore, it should be studied
further whether the BD affects ablation outcomes and which
factors besides the ablation-Tg level provide a better forecast
of the ablation success.
Based on the systematic review by Sawka et al. (7), there
are still no studies examining long-term recurrence or mortality rates in patients treated with an LID compared to an
unrestricted diet. Thus, further studies comparing the longterm outcomes in a strict LID group and less strict LID
groups, or regular-diet groups, may be required.
In conclusion, our results show that a strict LID for
one week is sufficient to achieve an adequate decreased of the
body iodine pool before RAIT. Because the results of the
current study were obtained in an iodine-rich area, we infer
that an LID period of less than one week may be sufficient for
patients who live in low dietary iodine intake areas. LID is a
laborious process for most DTC patients and reducing its
duration should have an immediate influence on patient
quality of life.
Author Disclosure Statement
All authors state that they have no competing interests,
financial or otherwise, to declare.
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LEE ET AL.
Address correspondence to:
Young Hoon Ryu, MD
Department of Nuclear Medicine
Yonsei University College of Medicine
Gangnam Severance Hospital
712, Eonjuro, Gangnam-Gu
Seoul 135-720
Korea
E-mail: [email protected]