The Current Practices and Perceptions of the

Low - Iodine Diet in the Treatment of Thyroid Cancer

Emily Kwan, B.Sc. (FNH) Dietetic Intern

Vancouver General HospitalJuly 8, 2003

Introduction

Total thyroidectomy - a common initial treatment for patients with differentiated thyroid cancer

Radioactive iodine (I-131) scanning - to ensure no residual tumor is present in the neck after the surgery

I-131 ablative therapy - to destroy cancer remnants and prevent disease recurrence

Introduction

Important to maximize the uptake of I-131 by thyroid remnants

– iodine-concentrating capacity of tumor cells is less effective than normal thyroid cells

– cumulative effect of total-body radiation --> limits the total amount of radiation one can receive

Introduction

How does a low-iodine diet "work"?

– iodine - normally absorbed by the thyroid gland for thyroid hormone production

– a LID depletes the thyroid of its natural stores of iodine

– when I-131 is administered, the thyroid will "suck up" the iodine because it has been so depleted of its natural stores

Current Problems

Some physicians/facilities do not support the need for dietary modifications prior to and/or after I-131 scans and treatments

Existing guidelines for LID vary among clinical studies, physicians, dietitians, and hospitals offering I-131 procedures

Current Problems

Inconsistencies in the existing guidelines include:

– level of iodine intake restriction

– duration of the diet

– use of diet for scans and/or treatments

– quality of dietary information

• verbal and/or written instructions

• food list (allowed and avoided)

• use of multivitamin or calcium supplements

• use of distilled water

Purpose of the Study

To examine the current practices and perceptions of physicians and dietitians regarding the use and efficacy of LID, and to compare them with the recommendations made in existing literature

Subjects and Methods Literature Review

– Medline, Pubmed, references cited in pertinent articles

Electronic Questionnaires

– developed two questionnaires (physicians and dietitians)

– used a combination of qualitative and quantitative questions

– reviewed by a physician and three dietitians prior to distribution

– sent out the web site address of the online questionnaires via emails/faxes

Subjects and Methods

Electronic Questionnaire (con'd)

– convenience samples of 22 physicians and 24 dietitians

– included at least one physician from each of the five hospitals (VGH, SPH, SMH, RJH, KGH) & four cancer centres (Vancouver, Fraser Valley, Vancouver Island, Southern Interior) in BC that are involved with I-131 patients

Subjects and Methods

Electronic Questionnaire (con'd)

– included at least one medicine/surgery/ oncology dietitian from the same five hospitals and four cancer centres

– also included some dietitians from other provinces due to limited availability of BC dietitians who would see patients for a LID

• provided insight of what out-of-province dietitians/physicians would recommend for a LID

Subjects and Methods

Patient Diet Information

– contacted the Nuclear Medicine Department of each of the five hospitals by phone

– conducted brief and informal phone interviews with either the nuclear medicine supervisor or physician

– received their patient information handouts via fax after the phone interviews

– also included three diet handouts provided by dietitians from other facilities

Literature Review

Very limited numbers of studies that examined the effectiveness of LID in the treatment of thyroid cancers

Goslings B.M. Effect of a Low-Iodine on I-131 Therapy in Follicular Thyroid Carcinomata. J Endocrinol 1975; 64: 30P.

– one of the earliest studies that examined the effect of a LID on thyroid cancer patients

Literature Review Maxon H.R., Thomas S.R., et al. Low Iodine Diet in

I-131 Ablation of Thyroid Remnants. Clin Nucl Med 1983; 8: 123-126.

Maruca J., Santner S., et al. Prolonged Iodine Clearance with a Depletion Regimen for Thyroid Carcinoma: Concise Communication. J Nucl Med 1984; 25: 1089-1093.

Lakshmanan M., Schaffer A., et al. A Simplified Low Iodine Diet in I-131 Scanning and Therapy of Thyroid Cancer. Clin Nucl Med 1988; 13: 866-868.

Literature Review

Each study had its own recommendations on iodine intake restriction level and duration of the diet

– LIDs: typically provided 30 - 50 ug iodine/day

– DRI: 150 ug iodine/day

– Average Canadian intake: 1000 ug iodine/day

– Duration of the diet ranged from 4 to 14 days

Literature Review

Maxon et al (1983) and Lakshmanan et al (1988) also included in their studies a list of foods that were allowed or not allowed in a LID

High iodine foods should be avoided

– iodized salt, sea salt, dairy products, eggs, seafood, algae-containing foods, all breads containing iodates, all red colored foods and medications, and restaurant foods

Literature Review All demonstrated a positive relationship between

I-131 uptake in the thyroid and dietary iodine consumption – urinary iodine excretion levels were reduced

significantly – radiation dose to the tumor increased by as

much as two-fold Shorter retention time of iodine in metastatic tumor

as compared with normal thyroid tissue Unable to show improved ablation rates

Literature Review Morris L.F., Wilder M.S., et al. Reevaluation of the

Impact of a Stringent Low-Iodine Diet on Ablation Rates in Radioiodine Treatment of Thyroid Carcinoma. Thyroid 2001; 11: 749-755.– 50 regular diet patients vs. 44 LID patients– ablation rate in patients following a LID was

numerically but not statistically greater than those following a regular diet

– recommended routine prescription of LID due to its potential effect and little cost

– suggested a less stringent diet that simply avoid high-iodine-containing foods might result in equivalent outcomes

Literature Review Pluijmen M., Eustatia-Rutten C., et al. Effects of

Low-Iodine Diet on Postsurgical Radioiodide Ablation Therapy in Patients with Differentiated Thyroid Carcinoma. Clin Endocrinol 2003; 58: 428-435. – 61 standard diet patients vs. 59 LID patients– concluded that a LID with a duration of 4 days is

sufficient to achieve iodine depletion– the only study thus far that has demonstrated

that a LID could improve the efficacy of thyroid remnant ablative therapy

Questionnaires Response rate:

– 36% (physicians), 62.5% (dietitians) Practices and perceptions of LID varied

significantly between facilities and between MDs and RDNs within the same facility

All physicians were aware of LID; 6 out of 8 physicians recommended it

7 out of 15 dietitians have had experience on LID counseling

Questionnaires

LID was not universally prescribed for I-131 scanning

Duration of diet ranged from 5 - 30 days before the procedure and 0 - 5 days after the procedure

Not all patients were told to remain on the diet after the I-131 treatment

Questionnaires

Level of iodine intake restriction

– do not usually recommend a specific level of iodine restriction

– only a few MDs/RDNs reported the use of a LID that provides 50 ug iodine/day

– more important to simply avoid high iodine foods

Questionnaires

Verbal vs. written diet instructions

Physicians

Dietitians

Verbal WrittenVerbal & Written

0

4 1

2 5

1

Questionnaires

Physicians' & dietitians' personal beliefs

– a mixture of opinions

– mostly skeptical about the diet

– important to find a balance between the benefits of LID and patients' compliance

– excellent educational material is essential

– MDs and RDNs should be consistent with their dietary advice

Patient Diet Handouts Foods allowed vs. foods to avoid

– Most LIDs limited or restricted the following high iodine foods:

• fish and seafood

• seaweed or seaweed by-products

• commercial breads and grain products

• dairy products (some allowed up to 1/2 glass/day)

• eggs (some allowed up to 3 eggs/week)

• table salt

• multivitamin/mineral supplements containing iodine

• red, orange, or brown processed foods and medications

• restaurant, manufactured, and processed foods

Patient Diet Handouts

Inconsistent diet instructions

– duration of the diet

– use of calcium supplements

– foods allowed/not allowed

– level of iodine intake restriction

– use of distilled water

Patient Diet Handouts

Quality of dietary instructions

– few lines to 10 pages

– some provided sample menus, recipes and information on where to purchase certain food products

– some provided detailed information on what foods are allowed/not allowed in each food category; some simply provided a list of foods to avoid

– specified number of servings and serving sizes of foods for each food category

Conclusion

Inconsistencies of current practices and perceptions among physicians and dietitians on the LID have been confirmed by this study

Recommendations Consistent diet recommendations essential

Duration of diet should be dependent on the nature of procedure

Verbal instructions should be routinely provided by MDs

Written diet instructions should be available to all patients receiving I-131

Recommendations

Referral to RDN if needed

Provide contact info of a RDN

Revise current LID recommendations

– shorter duration - 4 days vs. traditional 7-14 days

– liberalized approach

Recommendations

Liberalize the diet

– avoid high iodine foods

– allow small amounts of eggs, milk & cheese

– do not over-restrict meat, vegetables, fruits, grains & cereals as they are generally lower in iodine content

Recommendations

1200 mg calcium carbonate daily

Distilled water not required in GVRD

Inpatients should be put on a LID routinely

Angie Bowman Karol Traviss

Theresa CividinTracey Kerr

Dr. Hay Dr. Powe

Dr. Worsleyand all the doctors and dietitians who have

participated in the questionnaire study

SPECIAL THANKS