TBI and Thyroid Therapy

Indications for Whole Body I-123 (TBI)

Ectopic thyroid tissue (Substernal goiter, mediastinal mass), Lingual thyroid tissue, Ovarian Struma, Thyroid Carcinoma

Ovarian stroma

Functioning thyroid tissue in ovaries, actively concentrates I-123 and I-131

Thyroid Carcinoma Accounts for __ of all types of cancer

2%

Categories of thyroid cancer

undifferentiated and undifferentiated

Undifferentiated thyroid cancer

anaplastic, medullary

Differentiated thyroid cancer

Papillary, follicular, Hurthle cell

Anaplastic thyroid cancer

1% of thyroid cancers

Peak onset >65 years

Fast growing, metastasizes quickly

Usually fatal within 12 months after diagnosis

Cells do not look or act like normal thyroid cells*

Does not organify I-131

External radiation and chemo also have little effect

Medullary thyroid cancer

•~3% of thyroid cancers

•Neuroendocrine tumor of the parafollicular cells

•Sometimes called C cells because they produce calcitonin

•Calcitonin levels used as a tumor recurrence marker

•Can be caused by a genetic syndrome - Multiple Endocrine Neoplasia Type 2 (MEN2)

•25% of all MTC is familial

•Metastasizes very quickly

•lymph nodes, lungs, and liver

•Octreoscan/PET (FDG and DOTATATE) used to localize neuroendocrine receptor sites (cancer sites)

•Low affinity for I-131, not generally used for therapy

•External beam radiotherapy used

What genetic syndrome can cause medullary thyroid cancer?

Multiple endocrine neoplasia type 2

Differentiated thyroid carcinoma characteristics

•Under microscope they appear near-normal compared to other thyroid cells*

•Develop from thyroid follicular cells

•Slow growing and metastatic

•Very receptive to treatment: Surgical resection, I-131 therapy, Organify Iodine, but not as efficiently as normal thyroid cells

Papillary Thyroid Carcinoma

•80% of thyroid cancers

•Commonly metastasizes to cervical lymph nodes

•Most frequent in women 30-40 y/o

Predominant thyroid cancer in pediatric patient

Follicular Thyroid Carcinoma

•15% of thyroid cancers

•Most common in women >50 y/o

•Commonly metastasizes to lung and bone

Hurthle Thyroid Carcinoma

•Variant of Follicular Thyroid Ca

•Metastasizes to lymph nodes

Thyroid Cancer Treatments

•Surgical removal of tumor

•Baseline TBI

•Follow with I-131 ablation therapy (differentiated)

•If thyroid is fully ablated:

•Blood thyroglobulin levels should be zero

•Most sensitive test

•I-123 scan should show no focal uptake

•Localizes area of Iodine organification

•Return in 3-6 months for follow-up TBI

•Repeat I-131 therapy if any residual tissue is found

If thyroid is fully ablated

Blood thyroglobulin levels should be zero

I-123 scan should show no focal uptake

•Localizes area of Iodine organification

Thyroid Post-Surgery or Therapy

Patient placed on thyroid hormone replacement therapy, sually synthroid (T₄), or cytomel (T₃)

Thyroid hormone therapy causes the pituitary to suppress thyrotropin (TSH) secretion. With no TSH in circulation, any imaging will result in a false negative scan

Thyrotropin (TSH) must be present for residual thyroid cells to take up iodine. In order for the pituitary to supply it, the body must be free of excess T₃ and T₄

Because no T₃ or T₄ can be present, patient must be off their meds for TBI scan. Stop Synthroid for 6 weeks, Cytomel for 2 weeks. Patient will experience symptoms of hypothyroidism

If patients don’t want to go off thyroid meds for scan,

can give thyrogen (synthetic TSH, causes residual thyroid tissue to crave iodine)

Thyrogen elimination half life

15-35 hours

Whole Body I-123 Scan (TBI) Withdrawal

•Patient NOT ON thyroid medication! Stop Synthroid 6 weeks, Cytomel 2 weeks prior (8 week total). Patient on low iodine diet starting 2 weeks prior to scan. No CT contrast within 8 weeks

•Administer 5 mCi of I-123 and instruct patient to return in 24 hours. Obtain whole body scan and chest SPECT/CT at 24hr. MED collimator, I123. No kleenex in pockets. Whole body scan -10 cm/min - to include standard by feet in phantom. Standard should be secured in phantom and calibrated. SPECT/CT image through lung field. Split Display

Thyrogen Whole Body I-123 Scan

Patient ON thyroid medication!. Patient on low iodine diet starting 2 weeks prior to scan

Day 1: Baseline TSH, Thyroglobulin (serum), questionnaire, Give injection of Thyrogen 0.9mg IM.

Day 2: Give injection of Thyrogen 0.9mg IM.

Day 3: TSH, Thyroglobulin (serum). Administer 5 mCi 123I. Give injection of Thyrogen 0.9mg IM (if in conjunction with 131 therapy)

Day 4: TSH, Thyroglobulin (serum). Obtain whole body scan and chest SPECT/CT at 24hr.

TBI ROIs

Standard, thyroid, WB background, thyroid background (shoulder)

TBI normal % of dose

<0.1

I131 comes from

fission product of Uranium 235

I131 emits

beta emissions with tissue penetration of 0.6-2 mm

I-131 Thyroid Therapy limiting factor

bone marrow ablation

I-131 Thyroid Therapy used for

Hyperthyroidism, Differentiated thyroid carcinoma

I131 therapy female requirements

•All females 13-55 must have blood pregnancy test within 72 hrs of therapy

•Unless surgically sterilized and documented

•If breast feeding, must stop 5 days prior to therapy

•Limits radiation exposure to mammary tissue

•No resumption of breast feeding

•Avoid pregnancy for the next six months

I131 thyroid therapy dose determined by endocrinologist based on

gland size and 24 hour uptake value

Normal I131 thyroid therapy dose

20 mg

I131 therapy dose < 33 mCi

released with restrictions

I131 therapy dose 33-149.9 mCi

released with restrictions

I131 therapy dose > 150 mCi

Hospitalized until < 7mR/hr at 1 meter

I-131 Thyroid Therapy <33 mCi instructions

2-3 days

• Drink 8 glasses of water per day

• Use separate bathrooms, double flush

• Do not share food or prepare food for others

• Wash clothes separately

• Wipe down touched surfaces

• Shower daily

• Stay 3 ft from people (5+)

• Stay 6 ft from kids and pregnant women

4-8 days

•Suck on hard candy or chew gum

•Sleep alone

•No kissing or intercourse

•Stay 3 ft from kids and pregnant women

20 days

• Do not hug or hold kids for more than 10 minutes

• Do not sleep with pregnant woman

I-131 Thyroid Therapy >33 and < 149.9 mCi instructions

similar instructions as <33mCi…

•4 days: stay in separate home from kids

•Do not sleep with pregnant woman for 35 days

I131 Thyroid therapy >150 mCi procedure

•Patient changes into gown, regular clothes are bagged and put in room closet

•Dosed in hospital unit trained in handling radioactive patient items

•Floor is papered and non removable items are covered in plastic

•15 minutes after administration, monitor with survey meter at 1 meter to determine exposure rate in mR/hr

•Measure daily, 1 meter from chest, until patient is below 7 mR/hr

•Dismiss patient with outpatient <33 mCi restrictions

•What goes in, does not come out!

•Post Therapy Scan

•Radiation safety will decontaminate the room

Post therapy scan

•Confirm the efficacy of the therapy

•Will match or have better uptake than TBI

•High Energy Collimator

•I131

•10 cm/min

•Inpatients changed out of gown, pockets emptied

•New we add a standard

Other Scanning Methods for Thyroid Cancer Detection

PET Scanning: All types of thyroid cancer can be seen. Indicated when patient has had a negative TBI, but elevated thyroglobulin levels. 15 mCi of F-18 FDG