Thyroid Therapy

Question 1

Four types of thyroid cancers

Answer 1

1) papillary carcinoma
2) follicular carcinoma
3) medullary carcinoma
4) anaplastic

Question 2

describe the thyroid uptake and scan for a papillary carcinoma

Answer 2

normal uptake
multifocal and can cause mets to lymph nodes, lungs, bones, and brain

Question 3

describe the thyroid uptake and scan for a follicular carcinoma

Answer 3

normal uptake
usually unifocal + larger in size
greater likelihood of mets in bones and lungs

Question 4

describe the thyroid uptake and scan for a medullary carcinoma

Answer 4

normal uptake
doesn’t concentrate iodine but mets may concentrate iodine including 201Tl + MIBI

Question 5

describe the thyroid uptake and scan for an anaplastic (undifferentiated)

Answer 5

normal uptake
small and giant cell type - giant rarely accumulates iodine

Question 6

what characteristics suggest malignancy in a nodule?

Answer 6

if it’s singular, large, firm, has irregular borders
if found in males between ages of 15-40Y

Question 7

what is the role of thyroid uptake results in thyroid ca workup?

Answer 7

allows for therapy dose calculation
allows for the assessment of residual uptake after thyroidectomy/ablation

Question 8

what does increased thyroglobulin in someone suspected of thyroid ca represent?

Answer 8

predicts ca growth in papillary and follicular carcinomas

Question 9

what are some complications associated with 131I therapies?

Answer 9

• ca induction (rare) but leukemia can be caused by frequent and extremely high doses
• BM suppression
• sialoadenitis
• thyroid bed pain
• nausea, vomitting
• lung fibrosis
• transient oligospermia

Question 10

ablative doses are most commonly…

Answer 10

1110-5550 MBq

Question 11

dose for ablation of post-operative thyroid bed remnants

Answer 11

2750-5550 MBq

Question 12

dose for thyroid ca and mediastinal node involvement treatment

Answer 12

5550-7400 MBq

Question 13

dose for the treatment of distant mets

Answer 13

> 7400 MBq

Question 14

what factors might require an increased radio iodine dose to treat thyroid ca?

Answer 14

• mets esp. lungs or bone
• residual thyroid tissue

Question 15

what precautions would be appropriate after administration of a therapeutic radio iodine dose?

Answer 15

• no pregnancy for 3 mos
• flush twice
• limit contact with others, particularly children

Question 16

What is the Hurthke cell variant? how is it different?

Answer 16

it is a variant that fits the criteria of a follicular carcinoma
difference is that it doesn’t accumulate iodine

Question 17

what is PTU? how does it work?

Answer 17

propylthiouracil - anti-thyroid med

it inhibits synthesis of thyroid hormones; inhibits thyroid peroxidase to prevent oxidation of iodide to iodide

Question 18

what is tapazole? how does tapazole work?

Answer 18

an anti-thyroid medication
it inhibits synthesis of thyroid hormone by the same mechanism as PTU

Question 19

what is the generic name for tapazole?

Answer 19

methimazole

Question 20

why does 131I make a good therapy agent?

Answer 20

beta particle emitter of 606 keV which can damage follicular cells

Question 21

definition of target portion

Answer 21

portion taken up by the thyroid

Question 22

definition of non-target portion

Answer 22

dose that is rapidly excreted

Question 23

how is 131I excreted?

Answer 23

by glomerular filtration - 75% of nontarget by kidneys at 24HR

Question 24

patient prep. Thyroid scan
does the patient need to be fasting?

Answer 24

yes. for at least 4HR prior to administration + for at least 2HR post ingestion

Question 25

patient prep.
how long does the patient have to stop breastfeeding?

Answer 25

6 WEEKS prior to app
breastfeeding can no longer be done for this child

Question 26

3 ways to calculate thyroid therapy (hyperthyroidism) dose

Answer 26

1. fixed dose
2. activity based (Bq/g)
3. dose based (cGy/g)

Question 27

for activity based calculations, the specific MBq/g is chosen depending on…

Answer 27

• presence of nodules
• %RAIU
• pathology present
• age

Question 28

formula to calculate by activity based.

Answer 28

dose = (size of gland (g) * X MBq/g)/%RAIU

Question 29

formula to calculate by dose based

Answer 29

dose = (cGy desired * thyroid weight * 6.67)/T(days) * 24HR RAIU

Question 30

no hospitalization and minimal precautions

Answer 30

<300 MBq
<4uSv/hr at 2m

Question 31

can be released, but if hospitalized, certain precautions

Answer 31

<1100 MBq
<16 uSv/hr at 2m

Question 32

hospitalized

Answer 32

> 1100 MBq
16 uSv/hr at 2m

Question 33

which are well differentiated thyroid ca?

Answer 33

papillary and follicular

Question 34

how does papillary ca spread?

Answer 34

through lymph nodes

Question 35

which thyroid ca take up iodine and which doesnt?

Answer 35

up: papillary and follicular
don’t: medullary and anaplastic

Question 36

why do you want TSH to be high prior to administration?

Answer 36

• TSH stimulates the tissue to concentrate iodine + produce hormone
• thyroid tissue itself will have that iodine so the remnant tissues will uptake radioiodine

Question 37

ideal TSH range

Answer 37

> 30uU/ml
(ideally >50 uU/ml)

Question 38

how is the appropriate TSH level achieved?

Answer 38

• stopping hormone supplements
• stopping synthroid (T4) for 4-6 weeks
• stopping cytomel (T3) for 2-3 weeks
• giving rhTSH

Question 39

what are some adverse effects for ablation thyroid therapy?

Answer 39

• oral mucositis
• nausea/vomiting
• sialadenitis
• loss of taste, transient metallic taste
• painful thyroiditis