Investigation on low-iodine diet implementation by medical staff before radioactive iodine treatment for differentiated thyroid carcinoma.

OBJECTIVE: To explore the implementation of low-iodine diets by medical staff caring for patients with differentiated thyroid carcinoma prior to 131I therapy across 58 hospitals, and offer valuable insights for the development of guidelines on low-iodine diets. METHODS: Convenience sampling was utilized to conduct a survey among 163 medical staff members working in nuclear medicine departments across 58 tertiary hospitals using a self-designed questionnaire. RESULTS: Concerning the duration of the low-iodine diet prior to treatment, the medical staff's recommendations were as follows: 58.28% suggested 2-4 weeks, 31.29% recommended more than 4 weeks, 9.2% opted for 7-13 days, and 1.23% favored less than 1 week. Regarding the timing of resuming a normal diet, the respondents' recommendations ranged from immediately after treatment (1.84%) to 3 months post-treatment (8.58%), with intermediate recommendations of 2 h (8.58%), 24-48 h (14.11%), post-discharge (12.26%), and 1 month (42.94%). Furthermore, the surveyed medical staff unanimously recommended abstaining from seafood, with 90.8% also advising against the consumption of iodized salt, 91.41% recommending avoidance of iodine-containing medications, and 71.17% advising caution with moderately high-iodine foods. Notably, 75.46% of the medical staff evaluated patient compliance with the low-iodine diet. When patients failed to adhere to the diet preparation, 33.74% of healthcare workers chose to proceed with treatment. In terms of guidance sources, 96.93% of respondents relied on relevant guidelines, 66.26% referred to the literature, and 49.69% drew upon their clinical experience. During hospitalization, 58.28% of the medical staff continued to guide patients on the low-iodine diet, while only 8.59% provided such guidance after discharge. Notably, only 20.25% of the staff considered consulting the nutrition department. CONCLUSION: This study underscored substantial variations in the duration and selection criteria for low-iodine diets, which were linked to a scarcity of standardized evaluations. Consequently, there is an urgent need for further research to establish detailed, practical, accessible, comprehensive, and dependable implementation programs for low-iodine diets.

Effect of previous administration of potassium iodine and different durations of low iodine diets for radioiodine therapy on the treatment of Graves' disease in iodine-rich areas.

PURPOSE: To examine whether adherence to a low-iodine diet (LID) enhances the therapeutic efficacy of radioiodine therapy (RAI) in Graves' hyperthyroidism (GH) in iodine-rich areas. METHODS: We retrospectively evaluated 185 patients with GH from Aichi (n = 114) and Hokkaido (n = 71) Prefectures. Patients aged ≥ 18 years with GH who underwent RAI between December 2012 and March 2022 were divided into subgroups based on pretreatment with anti-thyroid drug (ATD) or potassium iodide (KI). Patients were followed up with LID from 18 days (group A) or 7 days (group H) before RAI to 3 days after RAI. The dose of radioactive iodine 131 (131I) was adjusted to deliver > 100 Gy to the thyroid. The associations between urinary iodine concentration on UIC2 vs. 24hRU and UIC2 vs. the 1-year RAI success rate (SR) were investigated. RESULTS: Compared with UIC1, UIC2 was significantly decreased in all subgroups (P < 0.01). An inverse correlation between UIC2 and 24hRU was observed in the four groups; however, the difference was insignificant. The SR in groups A and H was 85% and 89%, respectively. Univariate analysis revealed no association between UIC2 and SR in each group. Additionally, stratification of the 185 patients into quartiles using UIC2 yielded no significant differences in SR (p = 0.79). CONCLUSIONS: LID sufficiently reduced UIC in patients undergoing RAI. Although a lower UIC2 may increase 24hRU, it did not increase the success of RAI. The benefit of LID in enhancing the efficacy of RAI in GH treatment remains uncertain.

Effects of a low-iodine diet in post-thyroidectomy thyroid cancer patients undergoing I131 therapy at the Vietnam National Cancer Hospital.

Background: I131 therapy is regarded as an "internal surgery" (i.e., a non-invasive approach involving no incision or bleeding) that supports "external surgery" (i.e., using a scalpel) in completely eradicating the root cause of thyroid cancer. Limiting iodine intake is of paramount importance in I131 therapy. I131 therapy protocols recommend that patients follow a low-iodine diet, ideally with a maximum iodine intake of 50 µg/day for two weeks before the I131 therapy. Methods: A pre-post compassion uncontrolled clinic intervention study was conducted on a group of over 70 post-thyroidectomy thyroid cancer patients with indications for I131 therapy at the Vietnam National Cancer Hospital from December 2020 to December 2022. Aim: It aimed to assess the effects of a low-iodine diet on post-thyroidectomy thyroid cancer patients with indications for I131 therapy. Results: The study found that following the intervention, the percentage of participants at risk of mild to moderate malnutrition, as assessed by the PG-SGA tool, decreased to 4.3% from 40.0% before the intervention, with a statistically significant difference of p < 0.001. There was a considerable improvement in the low calcemia level among the study participants, with 35.7% of patients experiencing hypocalcemia prior to the intervention, which reduced to 17.1% after the intervention. This difference was statistically significant (p = 0.01). The study also revealed a urinary iodine level improvement among the study participants. Before the intervention, patients' average urinary iodine level was 14.9 ± 11.3 µg/dl. Following the intervention, it reduced to 12.7 ± 3.9 µg/dl, although this difference was not statistically significant (p = 0.29). Patients' quality of life after adhering to the low-iodine diet tended to decline; however, the change in scores before and after the intervention did not show a significant difference. Conclusion: Despite its negative impact on patients' quality of life, active nutrition counseling and intervention during the low-iodine diet contributed to the substantial improvement in the hypocalcemia level and the reduced urinary iodine level among patients, which in turn could enhance the efficacy of the subsequent I131 therapy.

Measurements of elemental iodine in soy sauces in Taiwan using a modified microplate method.

Background: Soy sauce is widely used in a variety of Asian dishes to enhance flavor. Soybean and most soybean products, including soy sauces, are listed as prohibited foods in a low iodine diet. However, the iodine content in soy sauces is largely unknown. The aim of this study was to determine the iodine content in domestic soy sauces in Taiwan. Methods: Twenty-five different kinds of soy sauces were diluted with distilled water and with a dilution factor of fifty or above. Iodine concentrations of the diluted samples were measured colourimetrically based on the Sandell-Kolthoff reaction by a modified microplate method. All the measurements were repeated twelve times on three different days for determination of mean and standard deviation (SD), and coefficients of variance (CV). Serial dilution and recovery tests were also performed for validation. The results were confirmed by an inductively coupled plasma mass spectrometry (ICP-MS) method. Results: Among the twenty-five surveyed soy sauces, most of them (n=22) were iodine-free (<16 ug/L, and thus un-detectable). The iodine concentrations (mean ± SD) of the three iodine-containing soy sauces were 2.7 ± 0.1, 5.1 ± 0.2, and 10.8 ± 0.6 mg/L, respectively. The inter-assay, intra-assay and total CVs were all <5.3% for the modified microplate method. The results obtained by ICP-MS were consistent with those of the modified microplate method. The recovery rates in the serial dilution test and recovery test ranged from 94.7% to 118.6%. Two of the three iodine-containing soy sauces were supplemented with kelp extract, while the other one without kelp extract had the highest amount of salt among the three iodine-containing soy sauces. Therefore, we postulate that iodized salt instead of kelp extract is the source of higher iodine content in that sauce. Conclusion: The results suggest that most soy sauces are iodine-free and may be allowed during low iodine diets.

The utility of low-iodine diet in preparation for thyroid cancer therapy with radioactive iodine-A cohort study.

Objective: A low-iodine diet (LID) of <50µ iodine/day is recommended as preparation for radioactive iodine (RAI) therapy in patients with differentiated thyroid cancer (DTC). The 24-h urinary iodine excretion (UIE) is utilized to evaluate the iodine-depleted status. The aim of this study was to test the association between UIE and progression-free survival (PFS). Patients and methods: In total, 70 patients with intermediate- or high-risk DTC, post-total thyroidectomy, adhered to 2 weeks of LID and had UIE measured before RAI therapy. A Cox regression model was performed to study the contribution of UIE to PFS. Results: The study group consisted of 68% (48/70) of women, aged 41.5 [IQR 31.0, 54.0] years, with tumor size 2.8 [IQR 1.8-4.5] cm, and presence of distant metastases in 22.9% (16/70) of patients. Patients were treated with 1-5 RAI dosages with the median cumulative activity of 150 [IQR 102-314] mCi (5.5 [IQR 3.8-11.6] GBq). During the follow-up of 3.7 [IQR 1.5-6.5] years, 21.4% (15/70) of patients had disease progression. The risk of progression was significantly higher in patients with UIE ≥200 µg/day at the time of RAI administration than in those with UIE <200 µg/day (HR 3.35, 95% CI 1.09-10.34, and p = 0.02). However, the multivariate Cox proportional hazards regression analysis adjusted for age, tumor size, and presence of distant metastases suggested that only distant metastases were independently significantly associated with the risk of progression (HR 5.80 (1.17-28.67), p = 0.03). Conclusions: Although UIE ≥200 µg/day might be associated with worse PFS in RAI-treated DTC patients, the presence of distant metastases is a strong independent predictor of progression. Less stringent LID might be sufficient to achieve a UIE of <200 µg/day.

Could Urinary Iodine Be an Effective Predictive Factor for Thyroid Cancer After High Dose Radioactive Iodine Therapy?

OBJECTIVE: The study aimed to investigate whether urinary iodine concentration (UIC) and urinary iodine to creatinine ratio (UICR) measurements can act as markers for the curative effect of radioactive iodine (RAI) therapy. METHODS: A total of 337 patients who underwent RAI therapy between May 2018 and March 2020 were recruited. According to the levels of UIC or UICR, patients were divided into 6 groups: group A, UIC levels of <100 µg/L; group B, UIC levels ranging from 100 to 200 µg/L; group C, UIC levels of ≥200 µg/L; group D, UICR levels of <100 µg/g; group E, UICR levels ranging from 100 to 200 µg/g; and group F, UICR levels of ≥200 µg/g. Treatment and follow-up were defined according to the criteria used in the 2015 ATA guidelines. RESULTS: When dividing the 337 patients into 3 groups according to UIC levels, 50.7%, 22.6%, and 26.7% of patients were in the A, B, and C groups, respectively. Based on the UICR levels, 58.1%, 29.4%, and 12.5% of patients were in the D, E, and F groups, respectively. There was a significant positive correlation between UIC and UICR levels and iodine-131 uptake rates (P < .001). The excellent response rate was not significantly different between the UIC groups (P = .997) and the UICR groups (P = .634). In logistic regression analysis, UIC and UICR levels were not confirmed to be independent factors predicting the excellent response status, but an age of ≥55 years (OR = 0.373; P = .007) and Tg levels of ≥10 ng/mL (OR = 18.972; P = .001) were confirmed to be independent factors predicting the excellent response status at the end of follow-up. CONCLUSION: The UIC or UICR levels before RAI therapy did not compromise the therapeutic response to iodine-131.

Low iodine diet advice and differentiated thyroid cancer treatment: A historic exploration in three UK centres.

BACKGROUND AND AIMS: Patients with differentiated thyroid cancer are often advised to follow a low iodine diet (LID) one to two weeks before radioiodine remnant ablation (RRA). We describe treatment practices and ablation success rates in centres (C1, C2, C3) in the UK with different approaches to LID advice. METHODS: Historic cohort of patients with differentiated thyroid cancer treated with RRA in 2015/16 in C1 (n = 50, 1-week LID), C2 (n = 59, 2-week LID) and C3 (n = 108, no LID advice). Response to RRA was stratified as excellent, indeterminate, or incomplete by the adapted American Thyroid Association Dynamic Risk Stratification Score. RESULTS: There was little difference in age, sex and staging between centres, but the percentage receiving 1.1 GBq vs higher administered activities differed (C1:22%, C2:44%, C3:15%, p < 0.001). Excellent response was recorded for: C1:48%, C2:36%, C3:49% (p = 0.61). Differences in RRA preparation and outcome assessment at C3 precluded comparison across all centres. Adjusted odds ratio for excellent response at C2 vs C1 was 0.57 (95%CI: 0.25,1.32), p = 0.19. CONCLUSIONS: There was no evidence that advising a LID for 2-weeks before RRA improves outcomes compared to 1-week. For definitive recommendations on LIDs prior to RRA, a prospective multi-centre study with a more homogenous approach to patient management or, randomised controlled trial, is needed.

Low-Iodine Diet of 4 Days Is Sufficient Preparation for 131I Therapy in Differentiated Thyroid Cancer Patients.

CONTEXT: No consensus exists about the optimal duration of the low-iodine diet (LID) in the preparation of 131I therapy in differentiated thyroid cancer (DTC) patients. OBJECTIVE: This work aimed to investigate if a LID of 4 days is enough to achieve adequate iodine depletion in preparation for 131I therapy. In addition, the nutritional status of the LID was evaluated. METHODS: In this prospective study, 65 DTC patients treated at 2 university medical centers were included between 2018 and 2021. The patients collected 24-hour urine on days 4 and 7 of the LID and kept a food diary before and during the LID. The primary outcome was the difference between the 24-hour urinary iodine excretion (UIE) on both days. RESULTS: The median 24-hour UIE on days 4 and 7 of the LID were not significantly different (36.1 mcg [interquartile range, 25.4-51.2 mcg] and 36.5 mcg [interquartile range, 23.9-47.7 mcg], respectively, P = .43). On day 4 of the LID, 72.1% of the DTC patients were adequately prepared (24-hour UIE < 50 mcg), and 82.0% of the DTC patients on day 7 (P = .18). Compared to the self-reported regular diet, DTC patients showed a significantly (P < .01) lower percentage of nutrient intake (calories, protein, calcium, iodine, and water) during the LID. CONCLUSION: The 24-hour UIE on day 4 of the LID did not differ from day 7, and therefore shortening the LID from 7 to 4 days seems justified to prepare DTC patients for 131I therapy in areas with sufficient iodine intake and may be beneficial to maintain a sufficient nutritional intake during DTC treatment.

Urinary iodine concentration and radioactive iodine therapeutic response in patients with differentiated thyroid cancer.

Aim: Urinary iodine concentration (UIC) may assess radioactive iodine ablation. Materials & methods: According the 2015 American Thyroid Association guidelines, patients were categorized into low- to intermediate-risk or high-risk groups. The iodine concentration in the morning urine specimens was measured by the ceric ion-arsenious acid method. Results: In the low- to intermediate-risk group (113 cases), nonexcellent response (non-ER) was associated with higher UIC, higher UIC subgroups (p < 0.05), higher pre-ablative stimulated thyroglobulin levels (p < 0.01). In the high-risk group (68 cases), the non-ER rate was higher in the higher pre-ablative stimulated thyroglobulin group (p < 0.01), but not significantly different between the UIC and UIC subgroups (p > 0.05). Conclusion: The non-ER rate was related to UIC in the low- to intermediate-risk group; however, UIC did not affect the non-ER rate in the high-risk group.

Influence of Levothyroxine With Recombinant Human Thyroid-Stimulating Hormone on Urinary Iodine Excretion Before Radioactive Iodine Administration.

OBJECTIVE: Stimulation with recombinant human thyroid-stimulating hormone (rhTSH) before radioactive iodine administration for patients with thyroid cancer may increase the body iodine pool in the presence of continued levothyroxine; however, the precise significance of its influence remains unclear. METHODS: This was a prospective observational study conducted between March 2017 and August 2020. We measured the 24-hour urinary iodine excretion and urinary iodine-to-creatinine ratio in patients with thyroid cancer stimulated by rhTSH or thyroid hormone withdrawal (THW) before radioactive iodine administration. Oral iodine intake was controlled by a 7-day self-managed low iodine diet, followed by a strict 3-day low iodine diet while in the hospital. RESULTS: Overall, 343 subjects were included (rhTSH: n = 181; THW: n = 162). The mean levothyroxine dose in the rhTSH group was 115.2 µg daily. The median 24-hour urinary iodine and urinary iodine-to-creatinine ratio in the rhTSH group (71.0 [interquartile range, 57.5-88.0] µg/day and 80.0 [59.0-97.5] µg/gCr, respectively) were significantly higher than those in the THW group (42.0 [30.0-59.0] µg/day and 39.0 [28.0-61.3] µg/gCr, respectively; both P < .001). After propensity score matching by age, sex, body weight, and renal function (rhTSH: n = 106; THW: n = 106), consistent results for both values were observed for both methods. The increase in urinary iodine with the rhTSH method was smaller than the expected value calculated from the amount of levothyroxine. CONCLUSION: Urinary iodine excretion was significantly higher among patients with rhTSH stimulation than those with THW, indicating that the rhTSH method slightly increases the body iodine pool.

Analysis of the incidence and influencing factors of hyponatremia before 131I treatment of differentiated thyroid carcinoma.

BACKGROUND: Hyponatremia is a common clinical electrolyte disorder. However, the association between hyponatremia and acute hypothyroidism is unclear. Acute hypothyroidism is usually seen in patients who undergo preparation for radioactive iodine therapy. AIM: To analyze the incidence and influencing factors of hyponatremia in a condition of iatrogenic acute hypothyroidism in patients with differentiated thyroid cancer (DTC) before 131I treatment. METHODS: The study group consisted of 903 DTC patients who received 131I treatment. The clinical data before and after surgery, as well as on the day of 131I treatment were analyzed. According to the blood sodium level before 131I treatment, patients were divided into the non-hyponatremia group and hyponatremia group. Correlations between serum sodium levels before 131I treatment and baseline data were analyzed. Univariate analysis and binary logistic regression were performed to identify the influencing factors of hyponatremia. RESULTS: A total of 903 patients with DTC, including 283 (31.3%) males and 620 (68.7%) females, with an average age of 43.8 ± 12.7 years, were included in this study. The serum sodium levels before surgery and 131I treatment were 141.3 ± 2.3 and 140.5 ± 2.1 mmol/L, respectively (P = 0.001). However, the serum sodium levels in males and females before 131I treatment were lower than those before surgery. Patients aged more than 60 years and less than 60 years also showed decreased serum sodium levels before 131I treatment. In addition, the estimated glomerular filtration rate (eGFR) in males and females decreased before 131I treatment compared with those before surgery (P = 0.001). Moreover, eGFR in patients over 60 years and under 60 years decreased before 131I treatment, when compared with that before surgery. There were no significant differences in serum potassium, calcium, albumin, hemoglobin, and blood glucose in patients before surgery and 131I treatment (P > 0.05). Among the 903 patients, 23 (2.5%) were diagnosed with hyponatremia before 131I treatment, including 21 cases (91.3%) of mild hyponatremia and 2 cases (8.7%) of moderate hyponatremia. Clinical data showed that patients with mild hyponatremia had no specific clinical manifestations, while moderate hyponatremia cases were mainly characterized by fatigue and dizziness, which were similar to neurological symptoms caused by hypothyroidism and were difficult to distinguish. Correlation analysis showed a correlation between serum sodium before 131I treatment and the preoperative level (r = 0.395, P = 0.001). There was no significant correlation between blood sodium and thyroid-stimulating hormone (TSH) levels and urine iodine before 131I treatment (r = 0.045, P = 0.174; r = 0.013, P = 0.697). Univariate analysis showed that there were significant differences in age, sex, history of diuretic use, distant metastasis, preoperative blood sodium, blood urea nitrogen (BUN), eGFR, TSH and urinary iodine between the two groups (all P < 0.05). Logistic regression analysis showed that factors such as history of diuretic use, distant metastases, preoperative sodium and BUN were all influencing factors of hyponatremia. The Hosmer and Lemeshow test (c2 = 2.841, P = 0.944) suggested a high fit of the model. Omnibus tests of model coefficients indicated the overall significance of the model in this fitted model (P < 0.05). Preoperative serum sodium was a significant factor associated with pre-131I therapy hyponatremia (OR = 0.763; 95%CI: 0.627-0.928; P = 0.007). CONCLUSION: The incidence of hyponatremia induced by 131I treatment preparation was not high. Preparation for radioactive iodine therapy was not a risk factor for the development of hyponatremia in thyroid cancer patients.

Hyperthyroidism in Cats: Considering the Impact of Treatment Modality on Quality of Life for Cats and Their Owners.

In cats, hyperthyroidism can be treated in 4 ways: medical management with methimazole or carbimazole, nutritional management (low-iodine diet), surgical thyroidectomy, and radioactive iodine (131I). Each form of treatment has advantages and disadvantages that should be considered when formulating a treatment plan for the individual hyperthyroid cat. Medical and nutritional managements are considered "reversible" or palliative treatments, whereas surgical thyroidectomy and 131I are "permanent" or curative treatments. The author discusses how each treatment modality could be the optimal choice for a specific cat-owner combination and reviews the advantages and disadvantages of each treatment option.

A Survey of UK Centres on Low Iodine Diet Recommendations prior to Radioiodine Ablation Therapy for Differentiated Thyroid Cancer.

BACKGROUND: Guidelines suggest that a low iodine diet (LID) is advised prior to radioiodine ablation (RIA) for thyroid cancer. We aim to describe current practice regarding LID advice in the UK, determine uptake of the 2016 UK LID Working Group diet sheet and discover whether there are differences in practice. METHODS: We used an online survey distributed between November 2018 and April 2019 to centres in the UK that administer 131I. We asked questions on whether a LID is advised, for how long, how advice is presented, whether and how compliance is measured and whether treatment is delayed if LID advice is not followed. RESULTS: Fifty-six clinicians from 47 centres that carry out RIA for thyroid cancer responded. Forty-four centres (94%) advise a LID prior to RIA, the majority for 14 days (82%). Two-thirds of the centres use the UK LID Working Group diet sheet. Patients are told to resume normal eating when 131I is administered at 17 centres (39%), with 18 (41%) advising waiting for 24-48 h after administration. Most centres (95%) use only a simple question or do not assess compliance. Only 2 (5%) indicate that RIA would be delayed if someone said they had not followed LID advice. CONCLUSIONS: UK practice regarding LID prior to RIA for thyroid cancer is consistent with current guidelines, but non-adherence does not usually delay RIA. The UK Low Iodine Diet Working Group diet sheet is widely recognised and used. Practice could be improved by centres working to harmonise advice on when to restart a normal diet.

Pattern of urine iodine excretion with low iodine diet during preparation for radioactive iodine ablation in patients with thyroid cancer.

BACKGROUND: The optimal period of low iodine diet during preparation for radioactive iodine (RAI) ablation in an area with iodine-rich diet was investigated. METHODS: Ninety-four patients with thyroid cancer who underwent low iodine diet and RAI were prospectively allocated into 2 groups-thyroxine withdrawal or using recombinant human thyroid stimulating hormone (rhTSH) for TSH stimulation. Their urinary iodine excretion (UIE) patterns were analyzed. RESULTS: There was no clinicopathological difference between the 2 groups except for tumor size and lymph node status. The UIE (median iodine to creatinine ratio, I/Cr) in the withdrawal group on the 7th and 14th day were 18.3 and 17.9 µg/gCr, respectively, with adequate preparation rate of 93.3% on both days (cutoff value 100 µg/gCr). In the rhTSH group, the median I/Cr on the 7th and 14th day were 48.0 and 45.7 µg/gCr (adequate preparation rates 91.8% and 93.8%), respectively. CONCLUSION: One week of low iodine diet is sufficient preparation for RAI regardless of method of TSH stimulation.

Analysis of Iodine Content in Salts and Korean Sauces for Low-Iodine Diet Education in Korean Patients with Thyroid Cancer Preparing for Radioiodine Therapy.

PURPOSE: A low-iodine diet is necessary in patients about to undergo radioiodine therapy for thyroid cancer to decrease the competitive absorption of ingested nonradioactive iodine. This study aimed to assess the iodine concentrations in salts and basic Korean sauces, and to provide fundamental data for guidelines on a low-iodine diet before radioiodine therapy. METHODS: The iodine contents of refined salts, solar sea salts, fish sauces, and commonly used Korean sauces with added refined salt were determined by ICP-MS. RESULTS: The iodine content of refined salts was found to be very low (0.033 ± 0.05 µg/100 g) compared with that of solar sea salts (434 ± 73.6 µg/100 g). The iodine contents of Korean soy sauce, Korean soybean paste, Gochujang seasoned with refined salt were also very low (0.010, 0.044, 0.002 µg/100 g, respectively). However, the mean iodine contents of the shrimp and fish Jeots analyzed in this study were found to be 41.3 ± 4.2 and 24.8 ± 4.5 µg/100 g, respectively. CONCLUSION: This study is the first to investigate the iodine contents of the salts and basic sauces used in Korea. The results show that refined salts and Korean traditional sauces seasoned with them can be safely used in low-iodine diets before radioiodine therapy.

Predictive factors for the outcomes of initial I-131 low-dose ablation therapy to Japanese patients with differentiated thyroid cancer.

OBJECTIVE: To identify prognostic factors associated with a low-iodine diet (LID) and the amount of remnant thyroid tissue in Japanese patients with differentiated thyroid cancer (DTC) who received initial I-131 remnant ablation (RAI) using a fixed low dose of I-131 (1110 MBq). PATIENTS AND METHODS: In this prospective study, we enrolled 45 patients. Patients were classified into a self-managed LID group and a strict LID group. We measured the urinary iodine concentration on the day of RAI after patients consumed LID for 2 weeks. Thyroid-stimulating hormone-induced thyroglobulin (Tg) levels and I-131 uptake by the remnant thyroid tissue were also evaluated. A response-evaluation whole-body scan (WBS) was performed 6-8 months after RAI to determine the outcome of the therapy. RESULTS: Post-LID urinary iodine levels of the strict LID group tended to be lower than those of the self-managed LID group. Twenty-five cases (56%) showed absence of uptake, whereas 20 cases (44%) showed residual uptake on the response-evaluation WBS. There were no significant differences between "absence" and "residual" groups in urinary iodine concentrations and Tg levels (p = 0.253 and p = 0.234, respectively). However, significant differences were observed in I-131 uptake by the thyroid bed (p = 0.035). CONCLUSIONS: For patients following the current Japanese method of a 2-week LID, the urinary iodine concentration was not a predictive factor for the successful outcome of RAI. In contrast, low I-131 uptake by the thyroid bed, revealed by the scintigram after RAI, may serve as a favorable predictive factor.

Analysis of Iodine Content in Salts and Korean Sauces for Low-Iodine Diet Education in Korean Patients with Thyroid Cancer Preparing for Radioiodine Therapy / 대한핵의학회잡지

PURPOSE: A low-iodine diet is necessary in patients about to undergo radioiodine therapy for thyroid cancer to decrease the competitive absorption of ingested nonradioactive iodine. This study aimed to assess the iodine concentrations in salts and basic Korean sauces, and to provide fundamental data for guidelines on a low-iodine diet before radioiodine therapy.METHODS: The iodine contents of refined salts, solar sea salts, fish sauces, and commonly used Korean sauces with added refined salt were determined by ICP-MS.RESULTS: The iodine content of refined salts was found to be very low (0.033 ± 0.05 µg/100 g) compared with that of solar sea salts (434 ± 73.6 µg/100 g). The iodine contents of Korean soy sauce, Korean soybean paste, Gochujang seasoned with refined salt were also very low (0.010, 0.044, 0.002 µg/100 g, respectively). However, the mean iodine contents of the shrimp and fish Jeots analyzed in this study were found to be 41.3 ± 4.2 and 24.8 ± 4.5 µg/100 g, respectively.CONCLUSION: This study is the first to investigate the iodine contents of the salts and basic sauces used in Korea. The results show that refined salts and Korean traditional sauces seasoned with them can be safely used in low-iodine diets before radioiodine therapy.

Experiences with a low-iodine diet: A qualitative study of patients with thyroid cancer receiving radioactive iodine therapy.

PURPOSE: This study aimed to describe hormone interruption experiences related to not only physical problems, but also psychological, social, and spiritual problems, in patients who had undergone total thyroidectomy. METHODS: In-depth interviews were performed with five participants, four women and one man, aged between 28 and 58. The participants were subjected to high-dose radiation of 100-150 mCi and had experienced abrupt hormonal interruptions after undergoing total thyroidectomy. The analysis was conducted using Giorgi's descriptive phenomenological method. RESULTS: Five essential components emerged as the interviews were dissected: dietary disruption due to discomfort, distress from overall bodily congestion, feelings of isolation as normalcy is lost from their daily routine, spending daily life with unfamiliar functional declines due to the LID, a lethargic state due to the lack of a place to which patients could retreat from the stress of hormone absence. CONCLUSIONS: The participants showed insecurity and depression due to an unbalanced diet, limited activities, and an abnormal lifestyle induced by the treatment. This treatment-related information can help healthcare providers readily understand and alleviate symptoms of thyroid cancer patients treated with RAI therapy.

Dietary evaluation of a low-iodine diet in Korean thyroid cancer patients preparing for radioactive iodine therapy in an iodine-rich region.

BACKGROUND/OBJECTIVES: Despite the importance of a low-iodine diet (LID) for thyroid cancer patients preparing for radioactive iodine (RAI) therapy, few studies have evaluated dietary intake during LID. This study evaluated the amount of dietary iodine intake and its major food sources during a typical diet and during LID periods for thyroid cancer patients preparing for RAI therapy, and examined how the type of nutrition education of LID affects iodine intake. SUBJECTS/METHODS: A total of 92 differentiated thyroid cancer patients with total thyroidectomy were enrolled from Seoul National University Hospital. All subjects completed three days of dietary records during usual and low-iodine diets before (131)I administration. RESULTS: The median iodine intake was 290 µg/day on the usual diet and 63.2 µg/day on the LID. The major food groups during the usual diet were seaweed, salted vegetables, fish, milk, and dairy products and the consumption of these foods decreased significantly during LID. The mean energy intake on the LID was 1,325 kcal, which was 446 kcal lower than on the usual diet (1,771 kcal). By avoiding iodine, the intake of most other nutrients, including sodium, was significantly reduced during LID (P < 0.005). Regarding nutritional education, intensive education was more effective than a simple education at reducing iodine intake. CONCLUSION: Iodine intake for thyroid cancer patients was significantly reduced during LID and was within the recommended amount. However, the intake of most other nutrients and calories was also reduced. Future studies are needed to develop a practical dietary protocol for a LID in Korean patients.

Efficacy of Dietitian-instructed Low Iodine Diet for Radioiodine Remnant Tissue Ablation for Thyroid Cancer.

We evaluated the significance of dietary instruction (DI) for patients who are going on a low iodine diet (LID) as a preparation for remnant tissue ablation for thyroid cancer. DI was done by a dietarian using a dedicated handbook we have developed. To assess the effect of LID on depleting body iodine, urinary iodine concentration (UIC) in patients with post-surgical papillary thyroid cancer was measured twice, before and after LID. UIC on the day of radioiodine administration was compared with radioiodine uptake (RU) in the remnant tissue. Additionally, the association between clinical and lifestyle-related features of patients and the outcome of LID were investigated. A questionnaire survey was conducted to determine whether the DI helped patients go on LID. The mean value of UIC after the one-week LID was decreased to about 15% of the baseline value. There was a significant inverse correlation between UIC and RU (r= -0.694). Age and UIC before the start of LID were linked to successful outcome of LID. In the questionnaire survey, 84% of the participants answered that the handbook helped them go on a LID. Likewise, 80% answered that they could manage their LID without using the boil-in-the-bag low iodine food. LID successfully decreased UIC in patients undergoing remnant tissue ablation. DI by a dietitian may make a practice of LID easier.