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®)?
Which statement best reflects NRC patient-release concepts after I-131 therapy?
Ra-223 dichloride (Xofigo®) is most appropriately characterized as which therapy choice?