Radioisotope: Sodium iodide I131 MCQs With Answer

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Introduction: Sodium iodide I-131 (I-131) is a widely used radioisotope in diagnostic and therapeutic nuclear medicine, central to radiopharmacy and thyroid-targeted treatments. B. Pharm students must understand its physical properties, radiobiology, mechanism of thyroid uptake via the sodium-iodide symporter, preparation as an NaI solution, dosimetry, radiation safety, and regulatory considerations. Key topics include its 8.02-day physical half-life, beta and gamma emissions, clinical uses for hyperthyroidism and thyroid ablation, patient preparation, contraindications (pregnancy, breastfeeding), and handling/storage protocols. This focused review and the following MCQs will strengthen your pharmacological and practical competence with radioactive iodine. ‘Now let’s test your knowledge with 50 MCQs on this topic.’

Q1. What is the physical half-life of sodium iodide I-131?

  • 8.02 days
  • 6 hours
  • 30 years
  • 2 days

Correct Answer: 8.02 days

Q2. Which types of radiation are emitted by I-131?

  • Beta particles and gamma rays
  • Alpha particles only
  • Neutrons and positrons
  • Gamma rays only

Correct Answer: Beta particles and gamma rays

Q3. The therapeutic action of I-131 in thyroid disease primarily relies on which emission?

  • Beta particle emission causing local tissue damage
  • Gamma emission for external imaging
  • Alpha emission for high-LET damage
  • Neutron emission for activation

Correct Answer: Beta particle emission causing local tissue damage

Q4. I-131 is taken up into thyroid follicular cells principally via which mechanism?

  • Sodium-iodide symporter (active transport)
  • Passive diffusion across the membrane
  • Endocytosis of iodide-protein complexes
  • Carrier-mediated transport by albumin

Correct Answer: Sodium-iodide symporter (active transport)

Q5. The most common clinical indications for therapeutic I-131 include:

  • Hyperthyroidism and thyroid remnant ablation in cancer
  • Bone pain palliation and central nervous system tumors
  • Renal imaging and liver function tests
  • Cardiac perfusion studies

Correct Answer: Hyperthyroidism and thyroid remnant ablation in cancer

Q6. Which route of administration is typically used for sodium iodide I-131 therapy?

  • Oral solution/tablet
  • Intravenous bolus injection
  • Intramuscular injection
  • Inhalation aerosol

Correct Answer: Oral solution/tablet

Q7. Which of the following is a major contraindication to administering I-131?

  • Pregnancy
  • Controlled hypertension
  • Type 2 diabetes mellitus
  • Mild allergic rhinitis

Correct Answer: Pregnancy

Q8. Which decay product is formed after I-131 decays?

  • Stable xenon-131
  • Radioactive iodine-132
  • Stable iodine-127
  • Cesium-137

Correct Answer: Stable xenon-131

Q9. For dosimetry conversion, 1 mCi is equal to how many MBq?

  • 37 MBq
  • 0.037 MBq
  • 100 MBq
  • 1 MBq

Correct Answer: 37 MBq

Q10. A common single-dose range for treating hyperthyroidism with I-131 is approximately:

  • 10–15 mCi
  • 0.1–1 mCi
  • 500–1000 mCi
  • 0.01–0.1 mCi

Correct Answer: 10–15 mCi

Q11. Which factor increases thyroidal uptake of administered I-131?

  • Low dietary iodine intake
  • High circulating iodide from recent contrast media
  • Recent potassium iodide (KI) administration
  • Severe renal failure preventing excretion

Correct Answer: Low dietary iodine intake

Q12. Before diagnostic or therapeutic I-131 studies, which medication is often withheld to improve uptake?

  • Thionamides (e.g., methimazole, propylthiouracil)
  • Beta blockers (e.g., propranolol)
  • Antihypertensives (e.g., ACE inhibitors)
  • Insulin

Correct Answer: Thionamides (e.g., methimazole, propylthiouracil)

Q13. What is the main excretion route for sodium iodide I-131 following administration?

  • Renal (urine)
  • Fecal excretion via bile
  • Exhalation through lungs as gas
  • Secretion into sweat glands only

Correct Answer: Renal (urine)

Q14. Which safety strategy is most effective for reducing occupational dose when handling I-131?

  • Time, distance, and shielding
  • Using only latex gloves without shielding
  • Standing directly above the source briefly
  • Wearing multiple surgical masks

Correct Answer: Time, distance, and shielding

Q15. The effective half-life of I-131 in the thyroid considers which two components?

  • Physical half-life and biological half-life
  • Radiochemical purity and chemical half-life
  • Decay constant and Avogadro’s number
  • Gamma emission rate and beta emission rate

Correct Answer: Physical half-life and biological half-life

Q16. Which protective shielding material is commonly used to store I-131 vials in the radiopharmacy?

  • Lead (Pb) container
  • Aluminum foil
  • Glass beaker without shielding
  • Wooden box

Correct Answer: Lead (Pb) container

Q17. Radiochemical purity testing for NaI(I-131) ensures what?

  • The proportion of activity present as iodide ion versus impurities
  • The isotopic composition of tellurium precursors
  • The sterility of the solution only
  • Blood compatibility of the formulation

Correct Answer: The proportion of activity present as iodide ion versus impurities

Q18. Which agent is used to block thyroid uptake of radioactive iodine in accidental exposures?

  • Potassium iodide (KI)
  • Calcium gluconate
  • Activated charcoal
  • Deferoxamine

Correct Answer: Potassium iodide (KI)

Q19. The primary manufacturing source of medical I-131 is:

  • Fission of uranium in nuclear reactors yielding radioiodine as a fission product
  • Electrolysis of stable iodine-127
  • Direct chemical synthesis from xenon gas
  • Gamma irradiation of sodium chloride

Correct Answer: Fission of uranium in nuclear reactors yielding radioiodine as a fission product

Q20. For remnant ablation after thyroidectomy for differentiated thyroid cancer, typical activities of I-131 may range approximately from:

  • 30–150 mCi depending on protocol and disease stage
  • 0.5–2 mCi only
  • 1000–2000 mCi
  • 0.01–0.05 mCi

Correct Answer: 30–150 mCi depending on protocol and disease stage

Q21. A radiopharmacist measures I-131 activity using which instrument?

  • Calibrator (dose calibrator/radionuclide calibrator)
  • pH meter
  • Thermometer
  • Mass spectrometer for stable isotopes

Correct Answer: Calibrator (dose calibrator/radionuclide calibrator)

Q22. Which adverse effect is commonly associated with therapeutic I-131 involving the salivary glands?

  • Sialadenitis (inflammation of salivary glands)
  • Pulmonary fibrosis
  • Hearing loss
  • Renal failure

Correct Answer: Sialadenitis (inflammation of salivary glands)

Q23. When preparing an oral I-131 dose, what is an important labeling requirement?

  • Activity (MBq or mCi), radionuclide identity, date/time, and expiry
  • Only patient name without activity
  • Color code without text
  • Storage shelf number only

Correct Answer: Activity (MBq or mCi), radionuclide identity, date/time, and expiry

Q24. What is radionuclidic purity?

  • Fraction of total radioactivity due to the desired radionuclide
  • Fraction of radiochemical species in solution
  • Amount of non-radioactive contaminants
  • pH value of the radiopharmaceutical

Correct Answer: Fraction of total radioactivity due to the desired radionuclide

Q25. In a patient receiving I-131 therapy, which instruction reduces pediatric exposure when a parent must care for them?

  • Limit close contact time and maintain distance, use separate sleeping arrangements
  • Allow unrestricted hugging and sleeping together
  • Share utensils but avoid sleeping in same room
  • Only use handshakes for contact

Correct Answer: Limit close contact time and maintain distance, use separate sleeping arrangements

Q26. Which laboratory test is most relevant to evaluate before giving I-131 for thyroid ablation?

  • Thyroid-stimulating hormone (TSH) level
  • Liver function tests only
  • Serum lipid profile
  • Blood glucose

Correct Answer: Thyroid-stimulating hormone (TSH) level

Q27. What is the role of recombinant human TSH (rhTSH) in I-131 therapy planning?

  • Stimulates thyroid tissue to increase radioiodine uptake without thyroid hormone withdrawal
  • Reduces renal clearance of I-131
  • Acts as an antidote to I-131 radiation
  • Neutralizes free iodine in circulation

Correct Answer: Stimulates thyroid tissue to increase radioiodine uptake without thyroid hormone withdrawal

Q28. Which drug interaction can reduce I-131 uptake into the thyroid?

  • Potassium iodide or amiodarone pre-exposure
  • Short-acting insulin
  • Metformin
  • Oral contraceptives

Correct Answer: Potassium iodide or amiodarone pre-exposure

Q29. Radiopharmacy storage of I-131 doses requires documentation of:

  • Activity, decay correction time, and shielding location
  • Only the batch number without activity
  • Only the color of the vial top
  • Temperature once a month

Correct Answer: Activity, decay correction time, and shielding location

Q30. What is a likely acute adverse reaction specific to thyroid treatment with high-activity I-131?

  • Radiation thyroiditis causing neck pain and swelling
  • Immediate anaphylaxis in most patients
  • Severe hypoglycemia
  • Acute myocardial infarction directly due to I-131

Correct Answer: Radiation thyroiditis causing neck pain and swelling

Q31. Which monitoring device is commonly used to detect surface contamination with I-131 in a radiopharmacy?

  • Handheld Geiger-Müller survey meter or contamination monitor
  • Thermocouple
  • pH indicator strip
  • Mass balance scale

Correct Answer: Handheld Geiger-Müller survey meter or contamination monitor

Q32. The concept of “effective dose” in radiological protection combines which parameters?

  • Absorbed dose, radiation weighting factors, and tissue weighting factors
  • Only the number of becquerels administered
  • Patient age multiplied by exposure time only
  • Only the physical half-life of the radionuclide

Correct Answer: Absorbed dose, radiation weighting factors, and tissue weighting factors

Q33. Which patient population requires strict avoidance of I-131 therapy due to fetal thyroid risk?

  • Pregnant women at any stage
  • Adults over 65 years only
  • Patients with controlled hypertension
  • Patients with mild eczema

Correct Answer: Pregnant women at any stage

Q34. What immediate step should staff take after a small I-131 spill on a countertop?

  • Evacuate area, restrict access, and follow spill protocol with appropriate shielding and survey monitoring
  • Wipe with dry tissue and discard in regular trash
  • Pour water on it and leave the room unlocked
  • Ignore it if activity seems low

Correct Answer: Evacuate area, restrict access, and follow spill protocol with appropriate shielding and survey monitoring

Q35. Which parameter best defines the “specific activity” of a radiopharmaceutical like I-131?

  • Activity per unit mass of the element (e.g., MBq/μg)
  • Number of disintegrations per second only
  • pH per milliliter of solution
  • Volume of solvent used

Correct Answer: Activity per unit mass of the element (e.g., MBq/μg)

Q36. Which statement about breastfeeding and I-131 administration is correct?

  • Breastfeeding should be stopped because I-131 is secreted in breast milk
  • Breastfeeding is safe after a single diagnostic low-dose study without precautions
  • Breastfeeding increases I-131 clearance and is recommended
  • Only pasteurization is needed to make milk safe

Correct Answer: Breastfeeding should be stopped because I-131 is secreted in breast milk

Q37. A radiopharmacy must check sterility for I-131 doses intended for:

  • Parenteral products; oral aqueous solutions typically require particulate and sterility knowledge per guidelines if prepared under sterile conditions
  • Oral tablets only; sterility is never needed
  • All radiopharmaceuticals are non-sterile by default
  • Only for inhaled aerosols

Correct Answer: Parenteral products; oral aqueous solutions typically require particulate and sterility knowledge per guidelines if prepared under sterile conditions

Q38. Which regulatory document or practice is essential for releasing a therapeutic I-131 dose to a patient?

  • Verification of activity measurement, patient identity, prescription, and documentation of radiopharmacy checks
  • Only a verbal order from any nurse
  • Leaving the dose on a bench with a sticky note
  • Sending an email without physical dose checks

Correct Answer: Verification of activity measurement, patient identity, prescription, and documentation of radiopharmacy checks

Q39. In the event of accidental contamination of skin with I-131, immediate decontamination should include:

  • Remove contaminated clothing and wash skin with soap and water
  • Rub skin vigorously with alcohol only
  • Apply adhesive tape to remove contamination without washing
  • Cover skin with a bandage and wait

Correct Answer: Remove contaminated clothing and wash skin with soap and water

Q40. Which imaging modality uses the gamma emissions of I-131 for visualization?

  • Planar gamma scintigraphy or whole-body scan
  • MRI using magnetic resonance of iodine
  • Ultrasound with contrast iodine
  • Optical fluorescence imaging

Correct Answer: Planar gamma scintigraphy or whole-body scan

Q41. What is the major reason for encouraging hydration and frequent voiding after I-131 therapy?

  • To reduce radiation dose to the bladder and promote renal clearance
  • To concentrate the radionuclide in the bloodstream
  • To prevent salivary gland uptake entirely
  • To neutralize radioactivity chemically

Correct Answer: To reduce radiation dose to the bladder and promote renal clearance

Q42. Which laboratory quality control is critical for I-131 radiopharmaceuticals prior to release?

  • Activity assay accuracy and radionuclidic identity/purity checks
  • Complete genomic sequencing of the batch
  • Only color matching to a reference sample
  • Measuring viscosity only

Correct Answer: Activity assay accuracy and radionuclidic identity/purity checks

Q43. An example of an external contamination control in a radiopharmacy handling I-131 is:

  • Using designated sink areas and regular swipe tests for surfaces
  • Allowing food in the prep area to prevent hunger
  • Cleaning only once a month
  • Wearing regular clothing instead of protective gear

Correct Answer: Using designated sink areas and regular swipe tests for surfaces

Q44. Which of the following is a long-term potential risk after high-dose I-131 therapy?

  • Secondary malignancies (rare but recognized risk)
  • Immediate liver necrosis in all patients
  • Guaranteed infertility in all treated patients
  • Development of type 1 diabetes

Correct Answer: Secondary malignancies (rare but recognized risk)

Q45. Dose optimization for I-131 therapy should consider which of the following?

  • Disease extent, remnant size, patient age, renal function, and prior therapies
  • Only patient’s hair color
  • Only the day of the week
  • Only the hospital’s preference with no patient factors

Correct Answer: Disease extent, remnant size, patient age, renal function, and prior therapies

Q46. Which isotope impurity would most concern a radiopharmacist in an I-131 preparation?

  • Short-lived gamma emitters increasing unexpected dose
  • Non-radioactive sodium chloride
  • Trace amounts of ethanol
  • Sterile water

Correct Answer: Short-lived gamma emitters increasing unexpected dose

Q47. Which storage instruction helps minimize dose loss by decay calculation accuracy?

  • Record the exact assay time and apply decay correction to the administration time
  • Store without recording time because decay is negligible
  • Only note the date, not the time
  • Ignore decay correction for all therapeutic doses

Correct Answer: Record the exact assay time and apply decay correction to the administration time

Q48. When counseling a patient after high-dose I-131 therapy, which recommendation is important to reduce public exposure?

  • Maintain distance from others, avoid close contact, and follow specific time restrictions for sharing utensils and sleeping together
  • Immediately resume normal intimate contact without precautions
  • Go to crowded events to build immunity
  • Share food freely but avoid handshakes

Correct Answer: Maintain distance from others, avoid close contact, and follow specific time restrictions for sharing utensils and sleeping together

Q49. The term “carrier-free” when applied to I-131 means:

  • The radioisotope is present without stable (non-radioactive) iodine carrier, maximizing specific activity
  • The product has no packaging carrier
  • It is free for clinical use without prescription
  • It has been shipped without a transport carrier bag

Correct Answer: The radioisotope is present without stable (non-radioactive) iodine carrier, maximizing specific activity

Q50. For regulatory transport classification, I-131 packages must be labeled and handled according to:

  • International Atomic Energy Agency (IAEA) and local regulations for radioactive materials
  • Only postal regulations for regular mail
  • Food transportation guidelines
  • General household parcel services without special labeling

Correct Answer: International Atomic Energy Agency (IAEA) and local regulations for radioactive materials

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