Oral Exam - Therapy

Question 1

Empiric dosing for thyroid cancer

Answer 1

○ Low risk, post thyroidectomy: 50-100 mCi

○ Intermediate/highrisk,postthyroidectomy: 100-150 mCi

○ Lymphadenopathy: 125-175 mCi

○ Recurrent/residualdisease: 150-200mCi

○ Bonemetastases: 200mCi

○ Lungmetastases: 200mCi,keepingtotaldose
to lung < 80 mCi

Question 2

I131 for cancer therapy indications

Answer 2

• I-131 therapy decreases risk of death
• I-131 therapy decreases risk of recurrence

• I-131 therapy facilitates initial staging and follow-up
○ All patients with thyroid cancer
○ Generally administered within 6 months post
thyroidectomy
○ Serumt . hyroglobulin levels should be ≤ 2ng/mLif
ablation successful
○ Recurrence suspected if thyroglobulin levels rise over
time, particularly if > 10 ng/mL
– Thyroglobulin not specific for thyroid cancer,
however; it is made by normal thyroid tissue as well

○ If thyroglobulin > 10ng/mL and whole-body RAI scan
negative, consider F-18 FDG PET/CT

Question 3

I131 Patient Prep

Answer 3

○ Confirm no recent iodine load
– Wai t4-6 weeks after IV contrast to begin RAI scan and therapy
– Amiodarone
– Highdietaryiodine(e.g.,seakelpsupplements)

○ Most experts recommend low-iodine diet 1-2 weeks
prior to whole-body scan and therapy

○ ElevateTSHpriortowhole-bodyscanandRAItherapy
– Levothyroxine(Synthroid)withdrawalfor3weeksin
adults, 2 weeks in children

– Stimulation with human recombinant TSH (Thyrogen)
□ 3-dayprotocol (IM injection on days 1 and 2, day 3 scan and RAI therapy)
□ More expensive than withdrawal

• Pre-therapy RAI whole-body scan
○ Useful to evaluate for nodal, distant metastases, confirm RAI-avid disease in recurrence (> 1 cm), determine dose of I-131 therapy
○ Can use I-123 or I-131 for whole-body scan; however, I- 123 has better imaging characteristics than I-131

• Post-therapy whole body scan
○ 4-10 days following RAI therapy

Question 4

Side effects I131

Answer 4

• Nausea
• Sore throat
• Salivary gland complications 
○ Sialadenitis, xerostomia, salivary calculi
• Change in sense of taste
• Radiation thyroiditis
- Radiation lung fibrosis
- Bone marrow supression 
- Secondary malignancies

Question 5

I131 doses for Graves

Answer 5

○ Typically 15-20 mCi I-131 po

Question 6

I131 dose for toxic nodular disease

Answer 6

○ 20-30 mCi I-131po, sometimes 40 mCi

Question 7

Alternative treatments for hyperthyroidism

Answer 7

Surgical (if large TMNG)

Methimazole (used most commonly, hepatic toxicity/blood dyscrasias, once daily dosing)

PTU (Hepatic toxicity/blood dyscrasias, used during 1st trimester pregnancy)

Question 8

Radiation safety release requirements

Answer 8

I131 dose < 33 mCi = released to outpatient setting with written radiation safety precautions

I131 dose > 33 mCi = can be released with written safety precautions and estimated dose to bystanders < 5 mSv

Question 9

I131 for hyperthyroidism - complications

Answer 9

Thyroid storm
Radiation thyroiditis (often requires steroids)
Opthalmopathy complications - do steroid taper

Question 10

Lymphoma therapy

Answer 10

For relapsed or refractory low grade or follicular B cell lymphoma

Anti-CD20 targeted radiotherapy

In111-zevalin given first for biodistrubution

Y90-zevalin - cold rituximab given before; promotes better binding to tumour

Question 11

Hepatic metastases therapy

Answer 11

Yyttrium 90 radioembolization; pure beta; t1/2 64 hrs

Question 12

Hepatic radioembolization - contraindications

Answer 12

Disseminated extrahepatic metastases, liver failure, excessive lung shunt fraction on Tc-99m MAA scan, unavoidable extrahepatic perfusion

Question 13

Hepatic radioembolization - procedure

Answer 13

Tc-99m MAA embolization scan
○ Calculate lung shunt fraction (adjust dose for shunting), detect extrahepatic perfusion, calculate Yttrium-90 dose
○ Intra-arterial injection of 3-5 mCi Tc-99m MAA
- if shunt fraction less than 10%, no dose modifications needed

Tc-99m MAA imaging
○ Anterior/posterior static images of thorax/abdomen
○ SPECT or SPECT/CT images of upper abdomen

○ SPECT/CT of upper abdomen strongly recommended
– Confirm hepatic segment sembolized with MAA
correspond with malignancy
– Detect evidence of extrahepatic perfusion; common
sites include stomach, gallbladder, peripancreatic, 2nd
portion of duodenum and periumbilical
– Free pertechnetate can create false-positive mimic of
extrahepatic gastric perfusion
□ If thyroid activity is also present, then etiology is
free pertechnetate
□ Focal gastric uptake favors extrahepatic perfusion,
whereas free pertechnetate more likely involves
entire stomach

Question 14

Hepatic radioembolization - complications

Answer 14

○ Progressive pulmonary insufficiency secondary to
radiation pneumonitis: Very rare but fatal complication

○ Radiation pneumonitis occurs with > 30 Gy in a single
treatment, 50 Gy cumulative

• Delayed complication(s)
○ Cholecystitis: Microspheres through patent cystic artery
– Usually self-limited, rarely requires cholecystectomy
– Avoid by infusing distal to cystic artery origin, empiric
coil embolization
○ Gastritis, duodenitis, pancreatitis or esophagitis: Inadvertent intestinal microsphere deposition

Question 15

Radium benefits

Answer 15

○ 1st radiopharmaceutical therapy that extends survival in
patients with bone metastasis
○ 3.6 month median survival advantage compared to
placebo

Question 16

Ra-223 post-procedure

Answer 16

• CBC with differential every 3 weeks for evidence of hematopoietic recovery
• Ra-223: Up to 70% of patients show improvement in pain (20% complete pain response)
• May take 2-3 infusions (up to 3months) for pain relief

Question 17

Ra-223 alternatives

Answer 17

Sr-89

Semarium-153

Question 18

Contraindications to alpha or beta emittors

Answer 18

○ Patient at high risk for pathologic fracture/cord
compression (surgical, radiotherapy emergencies)
○ Hemoglobin < 90 g/L or 9 g/dL
○ White blood cells < 3,500 cells/mm3
○ Platelets < 600,000/mm3
○ Pregnancy, breast-feeding, and women of child-bearing
age
○ Life expectancy < 3months
○ DIC
○ Acute or chronic renal failure(GFR < 30 mL/min)

Question 19

Things to check before giving Ra-223

Answer 19

1st dose: Blood counts prior to treatment initiation
□ ANC ≥ 1.5 x 109/L, platelet count ≥ 100x109/L, and
hemoglobin ≥ 10 g/dL

Subsequent doses (doses2-6): Blood count prior to
treatment, order blood counts 1 week prior to therapy
□ ANC ≥ 1 x 109/L and platelet count ≥ 50x109/L

Question 20

Ra-223 or beta emittor complications

Answer 20

Myelosupression