8.1 Therapeutic Radiopharmaceuticals
Key Takeaways
I-131 NaI treats hyperthyroidism (typically lower mCi activities) and thyroid cancer remnant/metastatic disease (higher ablation activities); release hinges on NRC patient-release criteria, not a single fixed mCi cutoff alone
Lu-177 dotatate (Lutathera®) is PRRT for SSTR-positive GEP-NETs; co-infuse amino acids for renal protection and monitor marrow toxicity
Lu-177 vipivotide tetraxetan (Pluvicto®) targets PSMA-positive mCRPC; Ra-223 (Xofigo®) is an alpha bone-seeking agent for symptomatic bone mets without visceral disease
Sr-89 (Metastron®) palliates painful osteoblastic mets with beta emission and notable myelosuppression risk
Y-90 microspheres (SIR-Spheres® resin, TheraSphere® glass) deliver liver-directed beta therapy after MAA mapping; written directives and radiation-safety handling apply
8.1 Therapeutic Radiopharmaceuticals
Quick Answer: Therapy agents deliver beta or alpha dose at disease sites. I-131 NaI → hyperthyroid and thyroid-cancer ablation with release criteria and isolation teaching. Lu-177 products (Lutathera®, Pluvicto®) → SSTR/PSMA targets plus renal amino acids (Lutathera) and CBC monitoring. Ra-223 (alpha bone) and Sr-89 (beta bone palliation) vs Y-90 microspheres for hepatic radioembolization.
Therapeutic RPs deposit beta or alpha energy at disease targets while non-target organs set toxicity limits. Exam items pair indication → nuclide/chemistry → special handling → monitoring.
I-131 Sodium Iodide: Hyperthyroidism and Ablation
I-131 decays by beta emission (therapeutic local dose) plus 364 keV gamma (imaging/surveys). Oral NaI is trapped and organified in functioning thyroid tissue and differentiated thyroid cancer that retains NIS activity.
| Clinical goal | Typical activity concept (adult order-of-magnitude) | Notes |
|---|---|---|
| Hyperthyroidism (Graves, toxic nodule/goiter) | Often ~4–30 mCi (method- and gland-dependent) | Calculated vs fixed-dose; higher uptake may lower activity |
| Remnant ablation / adjuvant after thyroidectomy | Commonly tens of mCi (e.g., ~30–100 mCi classically discussed) | Risk stratification drives written directive |
| Known/metastatic DTC | Often higher activities (e.g., 100–200 mCi range historically taught) | Inpatient vs outpatient depends on release rules |
Know hyperthyroid ≪ cancer ablation and that written directives are required under NRC 10 CFR Part 35. Pregnancy is an absolute contraindication; document pregnancy testing per policy. Breastfeeding must stop. Recent iodinated contrast, amiodarone, or excess stable iodine can block uptake. Low-iodine diet and TSH elevation (withdrawal or rhTSH/Thyrogen®) apply mainly to cancer pathways.
Release Criteria Concepts (High-Yield)
NRC §35.75 allows release if the TEDE to any other individual is not likely to exceed 5 mSv (0.5 rem). Licensees may use default activity/dose-rate tables, patient-specific calculations, and/or measured dose rate (commonly discussed ≤0.07 mSv/h (7 mrem/h) at 1 m for I-131). Release is risk-based, not a single universal mCi lockout. Provide written instructions (sleep apart, bathroom hygiene, time/distance limits).
Major excretion is urine—private toilet teaching, contamination control for vomitus, and room/waste surveys per license. High-activity inpatients need time-distance-shielding plans and defined visitor/staff stay triggers.
Lu-177 Dotatate (Lutathera®) — PRRT for NETs
Lutetium-177 emits beta particles (therapy) and low-abundance gammas useful for post-therapy imaging. Dotatate targets somatostatin receptor subtype 2 (SSTR2) on well-differentiated GEP-NETs (and related SSTR-positive disease per labeling/indication).
| Item | Teaching point |
|---|---|
| Typical regimen | 7.4 GBq (200 mCi) IV every ~8 weeks × 4 doses (label-style) |
| Amino acid co-infusion | Lysine/arginine (or approved AA solution) before/during/after to reduce proximal tubular reuptake and renal dose |
| Antiemetics | Often needed (AA infusion and disease-related nausea) |
| Monitoring | CBC (myelosuppression), renal function, liver tests; delay/hold for severe cytopenias |
| Contraindications / cautions | Severe renal impairment, pregnancy, uncontrolled infection, severe marrow compromise—follow label and authorized user |
Cold SSA timing is coordinated so receptors remain available. Do not confuse with Pluvicto: both are Lu-177 but targets and co-meds differ (AA co-infusion is a Lutathera hallmark).
Lu-177 Vipivotide Tetraxetan (Pluvicto®) — PSMA Prostate Cancer
Pluvicto® binds PSMA on prostate cancer cells for PSMA-positive mCRPC after appropriate prior therapy per labeling.
| Item | Teaching point |
|---|---|
| Activity concept | 7.4 GBq (200 mCi) IV every ~6 weeks, up to 6 doses if tolerating |
| Key toxicities | Myelosuppression, dry mouth (salivary PSMA), nausea, fatigue, renal caution |
| Safety | Lu-177 handling; written directive; post-void/hygiene teaching (renal excretion) |
Ra-223 Dichloride (Xofigo®)
Radium-223 is an alpha emitter that behaves like calcium, localizing in bone mineral at sites of osteoblastic turnover.
| Item | Teaching point |
|---|---|
| Indication | CRPC with symptomatic bone metastases and no visceral metastatic disease (classic label concept) |
| Dose | 55 kBq/kg (1.49 µCi/kg) IV every 4 weeks × 6 |
| Advantage | High LET alpha; short range; CBC monitoring still required |
| Handling | Alpha precautions; blood/urine contamination control |
Sr-89 Chloride (Metastron®)
Strontium-89 is a beta emitter and calcium analog for painful osteoblastic metastases (palliation, not soft-tissue disease control).
| Item | Teaching point |
|---|---|
| Activity | Often 148 MBq (4 mCi) or ~1.5–2.2 MBq/kg |
| Toxicity | Significant myelosuppression; nadir weeks later; avoid if marrow critically low |
| Clinical use | Bone pain relief; may flare pain early; longer half-life than Sm-153 on comparison items |
Y-90 Microspheres: SIR-Spheres® and TheraSphere®
Yttrium-90 pure beta therapy in microspheres for SIRT/TARE of hepatic malignancy via hepatic arterial infusion.
| Product concept | Carrier | Teaching contrast |
|---|---|---|
| SIR-Spheres® | Resin microspheres | More embolic particle load concept |
| TheraSphere® | Glass microspheres | Higher specific activity per sphere |
Workflow: angiographic mapping + Tc-99m MAA (lung shunt, extrahepatic flow) → written directive → IR catheter delivery with residual activity assay and surveys. Contraindications include excessive hepatopulmonary shunt, uncorrectable extrahepatic deposition, and inadequate liver reserve. Y-90 has minimal gammas; post-therapy imaging is specialized (bremsstrahlung/PET), not an I-131 whole-body analog.
Cross-Cutting Therapy Safety
| Theme | Apply to |
|---|---|
| Written directive | All Part 35 therapeutic administrations |
| Myelosuppression labs | Lu-177 agents, Ra-223, Sr-89, high-dose I-131 |
| Renal protection | Amino acids with Lutathera; hydration teaching broadly |
| Identity + activity assay | Dual verification before administration |
| Contamination control | Body fluids (I-131, Lu-177, Sr-89, Ra-223) |
Selection map: thyroid tissue → I-131; SSTR NET → Lutathera; PSMA mCRPC → Pluvicto; symptomatic bone mets (alpha, no visceral) → Ra-223; beta bone palliation → Sr-89; liver-dominant arterial therapy → Y-90 microspheres. If an item names a commercial brand, map it to the nuclide and target first—then recall dose concept, co-meds, and the dominant toxicity (marrow, kidney, or liver reserve).
Why is an amino acid (lysine/arginine) co-infusion given with Lu-177 dotatate (Lutathera®)?
To block salivary PSMA receptors and prevent xerostomia
To competitively reduce proximal tubular reuptake of the peptide and lower renal radiation dose
To increase hepatic microsphere trapping during radioembolization
To organify iodine in residual thyroid tissue before ablation
Which statement best reflects NRC patient-release concepts after I-131 therapy?
Every patient receiving more than 5 mCi must remain inpatient for 5 half-lives regardless of dose rate
Release is permitted when the TEDE to others is not likely to exceed 5 mSv (0.5 rem), using activity, dose-rate, or patient-specific methods as allowed
Patients may be released only if no gamma emission is present
Written radiation precautions are optional if the patient lives alone
Ra-223 dichloride (Xofigo®) is most appropriately characterized as which therapy choice?
An oral beta emitter used first-line for Graves hyperthyroidism
A PSMA-targeted Lu-177 agent for visceral-dominant prostate metastases
An alpha-emitting calcium analog for CRPC with symptomatic bone metastases and no visceral disease
A resin Y-90 microsphere injected into the hepatic artery for NET PRRT
Sections you finish are checked off in the contents.