Gl Radio Ther i131

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EANM Procedure Guideline For Therapy with Iodine-131

I. PURPOSE

The purpose of this guideline is to assist nuclear medicine

practitioners in

1. evaluating patients who might be candidates for therapy

with iodine-131 (131I) for benign or malignant conditions

2. providing information for performing this treatment.

3. understanding and evaluating the sequelae of therapy.

II. BACKGROUND

A. Definitions

1. I-131 is a beta-emitting radionuclide with a physical

half-life of 8.0 days, a principal gamma ray of 364

keV and a principal beta particle with a maximum

energy of 0.61 MeV, an average energy of 0.192

MeV and a range in tissue of 0.8 mm.

2. Therapy in this context means the oral administration

of 131I as sodium iodide.

3. Benign conditions in this context mean Graves’

disease (diffuse toxic goitre), toxic or non-toxic

goitre, solitary hyperfunctioning toxic thyroid nodule

or benign thyroid remnants from cancer surgery.

4. Malignant conditions include differentiated thyroid

cancer that accumulates radioiodine or functioning

thyroid cancer metastases.



B. Background

Oral administration of 131I Iodide has been used to treat

benign and malignant conditions of the thyroid since the

1940’s. Physicians responsible for treating thyroid disease

should have an understanding of the clinical

pathophysiology and natural history of the disease

processes, should be familiar with other forms of therapy

and should be able to collaborate closely with other

physicians involved in managing the patient. The treating

physician should either see patients in consultation with the

physician assuming overall management of the patient’s

condition or be prepared to assume that role. The

physician should be appropriately trained and

experienced in the safe use and administration of 131I

therapy.

Clinicians undertaking unsealed source therapy must be

knowledgeable about and compliant with all applicable

national and local legislation and regulations.

The facility in which treatment is administered must have

appropriate personnel, radiation safety equipment,

procedures available for waste handling and disposal,

handling of contamination, monitoring personnel for

accidental contamination and controlling contamination

spread.



III. COMMON INDICATIONS

A. Benign disease

1. Hyperthyroidism

131I may be indicated as the initial or secondary

treatment of Graves’ disease, toxic multinodular

goitre or solitary toxic thyroid nodule. Avidity of the

thyroid gland for iodide must be sufficient to permit

accumulation of an adequate radiation dose.

2. Non-toxic multinodular/diffuse goitre

131I therapy has been used successfully to diminish

the size of non-toxic multinodular/diffuse goitre.

3.

Post operative ablation of benign thyroid remnant(s) after thyroidectomy.

a. A minimum of four weeks should elapse

between surgery and radioiodine therapy to

allow endogenous levels of TSH to rise to 30-

50 ulU/ml. TSH may not rise to this level if a

large volume of functioning thyroid tissue

remains.

b. Ability of the remnant to accumulate

radioiodine may be demonstrated by uptake

measurement or imaging

B. MALIGNANT DISEASE



1. Therapy of residual cancer, local and distant

metastases

The presence of thyroid tissue should be

documented, either by imaging or biopsy. A

rising thyroglobin titre is a useful indicator of

residual or recurrent thyroid cancer.

CONTRAINDICATIONS

1. Absolute

Pregnancy; breastfeeding

2. Relative

Unmanageable urinary incontinence

Uncontrolled hyperthyroidism

Active thyroid orbitopathy

IV. PROCEDURE

A. Facility

The facilities required will depend on national legislation for

the emission of beta and gamma emitting

radiopharmaceuticals. If in-patient therapy is required by

national legislation, this should take place in an approved

facility with appropriately shielded rooms and en-suite

bathroom facilities. The administration of 131I should be

undertaken by appropriately trained medical staff with

supporting scientific and nursing staff.



B.

Patient preparation

1. All patients:

a. Should have given a clinical history and

undergone physical examination. Therapeutic

alternatives should be reviewed.

b. Should have undergone Laboratory Medicine

testing appropriate to the condition with

results available to and reviewed by the

treating physician.

c. Should receive written and verbal information

about the procedure prior to receiving

therapy. This information should include

details of the procedure, potential

complications, side effects, alternatives, and

expected outcome. Written informed consent

should be obtained.

d. Should be instructed on how to reduce

unnecessary radiation exposure to family

members and members of the public. Written

instructions should be provided.

e. Iodide-containing preparations, iodine

supplements, thyroid hormones and other

medications that potentially affect the ability

of thyroid tissue to accumulate iodide

must be discontinued for a sufficient time prior

to 131I administration. (See table).



f. Must not have received iodine-containing

radiographic contrast for at least three to four

weeks prior to planned 131I therapy. In patients

who have received large contrast loads or

who have renal dysfunction, more time may

be required. (See table).

DRUG INTERACTIONS

Type of medication Recommended time of withdrawal

Antithyroid medication (e.g.

propylthiouracil

carbimazole)

3-7 days

Natural or synthetic thyroid hormone

( e.g. thyroxine, tri-iodothyronine)

2 weeks for tri-iodothyronine

4 weeks for thyroxine

Expectorants, vitamins, health food

preparations,

Sodium iodide

1-2 weeks, depending on iodide

content

Iodine containing medications (e.g.

amiodarone)

Variable, 1-6 months

Topical iodine (e.g. surgical skin

preparation)

1-2 weeks

Radiographic contrast agents

Intravenous or intrathecal ( water soluble)

Oral fat soluble ( e.g. cholecystography)

Oil based ( e.g. bronchography)

Myelographic ( oil based)

3-4 weeks

3 months

6-12 months

2-10 years

Table adapted in part from: Monograph: 131-I (iodide), European

Association of Nuclear Medicine



2. For outpatients

a. Regulations governing the maximum burden

of131

I and maximum dose rate at which a

patient may be released vary according to

national legislation.

b. For patients with thyrotoxicosis, recent

measurements of thyroid hormone levels (T3

and/or T4) and thyroid stimulating hormone

(TSH) should be available. For patients with

thyrotoxicosis, avidity of the thyroid gland for

iodide must be established. This can be

achieved quantitatively by radioiodine

uptake measurements or qualitatively by

thyroid scintigraphy. These procedures will

exclude silent thyroiditis or factitious

thyrotoxicosis. If neck uptake is not seen, a

pelvic image may exclude struma ovarii.

Interfering drugs or antithyroid medication

should be withdrawn prior to uptake

measurements as outlined above.

c. For patients with malignant conditions, thyroid

hormone medication must be withheld for a

time sufficient to permit an adequate rise in

TSH. This is at least ten days for triiodothyronine

(T3) and four weeks for thyroxine (T4). Patients

with a large burden of residual functioning

thyroid tissue may not have the desired rise in

serum TSH. Recombinant TSH may be used to



prepare patients for post surgical diagnostic

studies. Its role in preparing patients for high

activity 131I therapy is not established.

3. For inpatients

a. All patients

i. Should be informed of the radiation

precautions required.

ii. Any significant medical conditions

should be noted and contingency plans

made in case radiation precautions

must be breached for a medical

emergency.

iii. Nursing personnel must be instructed on

radiation safety.

iv. Nursing personnel may be provided

appropriate radiation monitors (film

badge, pencil dosimeters, etc.).

v. Concern about radiation should not

interfere with the prompt, appropriate

medical treatment of the patient,

should an acute medical problem

develop.



b. Patients undergoing ablation of thyroid

remnant

i.

Should be on a low iodide diet for

about one week prior to administration

of 131I therapy.

Dietary Sources of Iodide

Iodized salt

Milk/dairy products

Eggs

Marine seafood

Seaweed and kelp products

Bread made with iodide conditioners

Celery

Iodide containing multivitamins

ii. At least four weeks should have elapsed

between surgery and thyroid ablation.

iii. Imaging is essential to confirm the ability

of the tissue to take up 131I prior to

treatment

c. Patients undergoing post-ablation therapy for

residual, recurrent or metastatic disease.



i. Should be on a low iodide diet for

about a week prior to administration of

therapy.

ii. Thyroid hormone medications must be

withheld for a time sufficient to permit

an adequate rise in TSH. This is at least

ten days for triiodothyronine (T3) and

four weeks for thyroxine (T4). Patients

with a large burden of residual

functioning thyroid tissue may not have

the desired rise in serum TSH.

Recombinant TSH may be used to

prepare patients for diagnostic studies

in the post-surgical setting. Serum TSH

levels should ideally be greater than 30

ulU/ml.

iii. A running total of administered activity

of 131I should be kept in the patient’s

record.

iv. Imaging is essential to confirm the ability

of tissue to take up 131I prior to

treatment. Measurement of serum

thyroglobin level is also useful.

C. Information pertinent to performing the procedure

1.

For all patients



a. Female patients who have a potential to bear

children should routinely be tested for

pregnancy within a few days before the

administration of the 131I treatment.

Occasionally, for social reasons (e.g., women

who have taken the vows of celibacy) a

pregnancy test may be omitted.

b. All potentially breast feeding/lactating

women should be asked if they are breast

feeding/lactating. If so, breast-feeding should

stop and therapy delayed until lactation

ceases in order to minimize the radiation dose

to the breast. The patient may not resume

breast-feeding for that child. Breast-feeding

may resume with the birth of another child.

c. Assurance that the patient is continent of

urine or that arrangements are made to

prevent contamination caused by

incontinence.

2. For patients with thyrotoxicosis

a. Prior therapy and results with previous

radioiodine (including amount administered),

thionamides or surgery should be

documented.



b. Results of recent 24-hour RAIU or qualitative

evidence of iodide avidity of the thyroid.

c.

Estimated weight of gland based upon

imaging or palpation if calculation of

administered activity is to be performed.

d. The presence or absence of nodules in the

thyroid and their degree of function should be

noted.

e. Concomitant medications.

3. For patients with malignancy

a. Histologic diagnosis.

b. Evidence of functioning residual benign or

malignant thyroid tissue.

c. Total lifetime 131I administered activity may be

useful.

C. Precautions

1. For patients with thyrotoxicosis

a. Recent thionamide therapy usually increases

radioresistance by causing rapid turnover of

thyroidal iodine and by other mechanisms.

This may require a compensatory increase in

administered activity.



b. Hyperthyroid crisis can be precipitated in-

patients with large iodide avid multinodular

glands who are given large administered

activities. Such patients and patients who are

elderly, who suffer from known heart disease

or have a history of congestive heart failure

may need to be pre-treated with beta-

blockers and/ or started on thionamides a few

days after their radiodine treatment.

2. For patients with malignant disease

Treatment side effects may occur and are generally

dose-related. These include nausea and vomiting,

sialadenitis, xerostomia, neck swelling, and

cytopenia. These are rare with administered

activities below 7400 MBq (200 mCi). Hydration of

the patient with instructions urging frequent urination

for up to two weeks and efforts to increase salivary

flow may reduce radiation exposure to the bladder

and salivary glands. Antiemetics may be helpful.



D. Radiopharmaceutical: I-131

E. Radiation Dosimetry in Adults

Absorbed Dose Assuming No Thyroid Uptake

(Athyrotic)

ORGAN mGy/MBq

Bladder wall 0.610

Lower colon wall 0.043

Kidneys 0.065

Ovaries 0.042

Testes 0.037

Stomach 0.034

ICRP 53 (page 253)

Absorbed Dose, Assuming 55% Thyroid Uptake and 20

gram gland (Hyperthyroid)

Organ mGy/MBq

Thyroid 790

Bladder Wall 0.290

Breast 0.091

Upper colon wall 0.058

Ovaries 0.041

Testes 0.026ICRP 53 (page 278) based on a 20g gland

Administered

131I Activity

MBq

Thyroid

Uptake

(%)

Radiation Dose to the Red Marrow*

mGy/MBq

Adult Child (10yrs)

74-7400 MBq 0

5

35

45

55

0.035 0.065

0.038 0.070

0.086 0.160

0.100 0.190

0.120 0.220

* dose may vary depending on the whole body effective half-life of I-131ICRP53 pages 275-278



1. Calculation of administered 131I activity

a. For thyrotoxicosis

The main aim of treatment should be to

prevent persisting or recurrent hyperthyroidism.

Since the incidence and rate of appearance

of hypothyroidism is directly related to the

delivered thyroid radiation dose, the optimal

dose calculation for treatment should be

based on measurements that permit the

delivery of a specified and planned radiationbdose to the thyroid. This requires

measurement of thyroid uptake, gland size,

and an estimate of thyroidal turnover rate

(based upon several uptake measurements

over a period of one week). Many medical

centers find this method of calculating the

administered activity too onerous since it

requires that the patient return on several

occasions. As an alternative, most medical

centers assume a generic thyroidal turnover

rate. Many strategies have been proposed.

The approach used by each practice should

suit the practice setting.

i. Some attempt to deliver a specific

amount of radiation to the thyroid gland

on the basis of 131I absorbed per gram

of gland. This generally ranges from 2.2

–3.0 MBq/gm (60 – 80 uCi/gm) up to 6.0-

7.0 MBq/gm (160-180 uCi/gm). As a

general rule, smaller administered



activities are associated with higher

rates of treatment failure and lower

rates of post-treatment hypothyroidism.

ii. Some practices routinely deliver fixed

administered activity for all patients.

This may involve a small fixed amount

(74–111 MBq or 2–3 mCi), repeated as

necessary, a large fixed amount

(370–740 MBq or 10-20 mCi), or a sliding

scale, with the administered activity

based upon the size of the gland

and/or severity of thyrotoxicosis.

iii. For patients with nodular

hyperthyroidism and for patients

receiving repeat therapy for prior

treatment failure, larger administered

activities are usually needed.

b. For thyroid malignancy

i. For patients undergoing ablation of

thyroid remnant, administered activities

in the range of 3700–5500 MBq (100–150

mCi) are usually given.

ii. For patients undergoing re-treatment for

residual disease or local recurrence,

somewhat larger administered activities



(in the range of 5550 MBq (150 mCi) are

often used.

iii.

For patients with distant metastases,

administered activities of 7400 MBq (200

mCi) or more may be used. Caution is

recommended in patients with diffuse

lung metastases in view of the potential

risk of radiation fibrosis.

c.

Patients should have a whole body scan

performed one to two weeks after treatment

for staging purposes.

F. Sources of error

1. For hyperthyroid patients

Sources of inaccuracy may occur in the thyroid

uptake, the estimated weight of the gland and in

unpredictable variations in effective half-life or

radiation sensitivity of the gland.

2. For thyroid cancer

a. If administered activities of ≥74 MBq (2.0 mCi)

or more of 131I were used for the whole body

iodine scan, “stunning” of the thyroid

remnant or residual disease could alter the

effectiveness of therapy.



b. Some tumors may possess cells of different

radiosensitivity, which could predispose to

ultimate failure of therapy.

V. ISSUES REQUIRING CLARIFICATION

A. The role of recombinant TSH in treatment of patients still on

thyroid suppression.

B. The use of 131 I whole body imaging prior to 131I therapy for

thyroid cancer

and whether “ stunning” of the thyroid remnant occurs.

C. The necessity of treating small (<1.5 cm.) papillary thyroid

cancers with 131i.

D. Blind retreatment of 131I scan negative, thyroglobulin

positive patients.

VI.

CONCISE BIBLIOGRAPHY

1. Brill DR, Perez CA, at al. The American College of Radiology

Standard for the Performance of Therapy with Unsealed

Radionuclide Sources. American College of Radiology, 1996.

2. Barrington SF, Kettle AG, et al. Radiation dose rates from patients

receiving iodine-131 therapy for carcinoma of the thyroid. Eur J

Nucl Med 23: 123-30 (1996). Published erratum appears in Eur J

Nucl Med 1997: 24: 1545

3. Sparks RB, Siegel JA. The need for better methods to determine

release criteria for patients administered radioactive material.

Health Phys 1998: 75: 385-8.



4. MIRD Committee of Society of Nuclear Medicine. MIRD Dose

Estimate Report No. 5. J Nucl Med 1975; 16:587.

5.

Stabin M, Stubbs J, Toohey R. Radiation Dose Estimates for

Radiopharmaceuticals 30 April 1996. Radiation Dose Internal

Information Center, Oak Ridge, TN.

6. Schlumberger MJ. Papillary and follicular thyroid carcinoma.

NEJM 1998: 338: 297-306.

7.

Lerch H, Schober O, Kuwar T, et al. Survival of differentiated

thyroid carcinoma studied in 500 patients. J Clin Oncol 1997: 15:

2067-75

8. Mazzaferri EL, Robyn J. Post surgical management of

differentiated thyroid carcinoma. Otolaryngologic Clin N Amer

1996: 637-662

9. European Association of Nuclear Medicine. Monograph – [131-

I] Iodide. 1999.

10. International Committee on Radiation Protection (ICRP).

Publication 53. Pergamon Press. New York. 1987. 18 (275-8).

K. Zanzonico PB, Brill AB, Becker DV, et al. Radiation

Dosimetry: Chapter 9 p 106-134 in Principles of Nuclear

Medicine 1995 Ed. Wagner HN.

VI DISCLAIMER



The European Association of Nuclear Medicine has written and

approved guidelines to promote the cost effective use of high quality

nuclear medicine therapeutic procedures. These generic

recommendations cannot be rigidly applied to all patients in all

practice settings. The guidelines should not be deemed inclusive of all

proper procedures or exclusive of other procedures reasonably

directed to obtaining the same results. Advances in medicine occur at

a rapid rate. The date of a guideline should always be considered in

determining its current applicability.

VII DESCRIPTION OF THE GUIDELINE DEVELOPMENT PROCESS

The EANM Radionuclide Therapy Committee has been involved in the

process of guideline development for undertaking radionuclide

therapies since 1995. A multinational group of therapy experts

developed a series of monographs on the radioncuclide therapy

agents licensed for use throughout Europe. Subsequently a series of

protocols was published on the Internet for use by members of the

European Association of Nuclear Medicine. The monographs and

protocols were achieved through a process of consensus taking note

of the evidence available at the time of writing. The monographs and

protocols have been in the public domain for four years and

comments have been received from members of the nuclear

medicine community. The guidelines have been developed using

material within the monographs and protocols and have been

formatted to harmonise with the Society of Nuclear Medicine Therapy

Guidelines format.

Last amended: 14.02.2002

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