Thyroid Therapy Flashcards
Four types of thyroid cancers
1) papillary carcinoma
2) follicular carcinoma
3) medullary carcinoma
4) anaplastic
describe the thyroid uptake and scan for a papillary carcinoma
normal uptake
multifocal and can cause mets to lymph nodes, lungs, bones, and brain
describe the thyroid uptake and scan for a follicular carcinoma
normal uptake
usually unifocal + larger in size
greater likelihood of mets in bones and lungs
describe the thyroid uptake and scan for a medullary carcinoma
normal uptake
doesn’t concentrate iodine but mets may concentrate iodine including 201Tl + MIBI
describe the thyroid uptake and scan for an anaplastic (undifferentiated)
normal uptake
small and giant cell type - giant rarely accumulates iodine
what characteristics suggest malignancy in a nodule?
if it’s singular, large, firm, has irregular borders
if found in males between ages of 15-40Y
what is the role of thyroid uptake results in thyroid ca workup?
allows for therapy dose calculation
allows for the assessment of residual uptake after thyroidectomy/ablation
what does increased thyroglobulin in someone suspected of thyroid ca represent?
predicts ca growth in papillary and follicular carcinomas
what are some complications associated with 131I therapies?
- 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
ablative doses are most commonly…
1110-5550 MBq
dose for ablation of post-operative thyroid bed remnants
2750-5550 MBq
dose for thyroid ca and mediastinal node involvement treatment
5550-7400 MBq
dose for the treatment of distant mets
> 7400 MBq
what factors might require an increased radio iodine dose to treat thyroid ca?
- mets esp. lungs or bone
- residual thyroid tissue
what precautions would be appropriate after administration of a therapeutic radio iodine dose?
- no pregnancy for 3 mos
- flush twice
- limit contact with others, particularly children
What is the Hurthke cell variant? how is it different?
it is a variant that fits the criteria of a follicular carcinoma
difference is that it doesn’t accumulate iodine
what is PTU? how does it work?
propylthiouracil - anti-thyroid med
it inhibits synthesis of thyroid hormones; inhibits thyroid peroxidase to prevent oxidation of iodide to iodide
what is tapazole? how does tapazole work?
an anti-thyroid medication
it inhibits synthesis of thyroid hormone by the same mechanism as PTU
what is the generic name for tapazole?
methimazole
why does 131I make a good therapy agent?
beta particle emitter of 606 keV which can damage follicular cells
definition of target portion
portion taken up by the thyroid
definition of non-target portion
dose that is rapidly excreted
how is 131I excreted?
by glomerular filtration - 75% of nontarget by kidneys at 24HR
patient prep. Thyroid scan
does the patient need to be fasting?
yes. for at least 4HR prior to administration + for at least 2HR post ingestion
patient prep.
how long does the patient have to stop breastfeeding?
6 WEEKS prior to app
breastfeeding can no longer be done for this child
3 ways to calculate thyroid therapy (hyperthyroidism) dose
- fixed dose
- activity based (Bq/g)
- dose based (cGy/g)
for activity based calculations, the specific MBq/g is chosen depending on…
- presence of nodules
- %RAIU
- pathology present
- age
formula to calculate by activity based.
dose = (size of gland (g) * X MBq/g)/%RAIU
formula to calculate by dose based
dose = (cGy desired * thyroid weight * 6.67)/T(days) * 24HR RAIU
no hospitalization and minimal precautions
<300 MBq
<4uSv/hr at 2m
can be released, but if hospitalized, certain precautions
<1100 MBq
<16 uSv/hr at 2m
hospitalized
> 1100 MBq
16 uSv/hr at 2m
which are well differentiated thyroid ca?
papillary and follicular
how does papillary ca spread?
through lymph nodes
which thyroid ca take up iodine and which doesnt?
up: papillary and follicular
don’t: medullary and anaplastic
why do you want TSH to be high prior to administration?
- TSH stimulates the tissue to concentrate iodine + produce hormone
- thyroid tissue itself will have that iodine so the remnant tissues will uptake radioiodine
ideal TSH range
> 30uU/ml
(ideally >50 uU/ml)
how is the appropriate TSH level achieved?
- stopping hormone supplements
- stopping synthroid (T4) for 4-6 weeks
- stopping cytomel (T3) for 2-3 weeks
- giving rhTSH
what are some adverse effects for ablation thyroid therapy?
- oral mucositis
- nausea/vomiting
- sialadenitis
- loss of taste, transient metallic taste
- painful thyroiditis
