Radioactive Isotopes in Nuclear Medicine: Key Isotopes & Clinical Uses

Nuclear medicine uses radiopharmaceuticals—radioactive isotopes bound to targeting molecules—to diagnose and treat disease. Each isotope’s physical half‑life and emission type dictate its application.

Major Diagnostic Isotopes

Isotope	Half‑Life	Primary Emission	Common Uses
Technetium‑99m	6 hours	γ (140 keV)	Bone scans, cardiac stress (MIBI), renal, thyroid, brain, sentinel node
Thallium‑201	73 hours	γ, X‑ray	Myocardial perfusion (older agent)
Gallium‑67	78 hours	γ	Infection/inflammation imaging, lymphoma staging
Indium‑111	2.8 days	γ	White‑cell labeling, octreotide scan (NETs)
Fluorine‑18	110 min	β⁺ (PET)	FDG‑PET (oncology, cardiac, brain), amyloid/tau PET

Therapeutic Isotopes

Isotope	Half‑Life	Emission	Uses
Iodine‑131	8 days	β⁻, γ	Thyroid cancer ablation, hyperthyroidism
Lutetium‑177	6.7 days	β⁻, γ	PRRT for NETs (Lutathera), PSMA therapy (prostate)
Yttrium‑90	64 hours	β⁻	Radioembolization (liver), radiosynovectomy
Radium‑223	11.4 days	α	Metastatic castration‑resistant prostate cancer (bone)

Safety & Logistics

• Short half‑lives minimize radiation exposure but require on‑site generators (⁹⁹Mo/⁹⁹ᵐTc) or rapid delivery (¹⁸F).
• ALARA principle: As Low As Reasonably Achievable dose to patients/staff.
• Pregnancy/breastfeeding precautions per isotope.

Emerging Trends

Theranostics—paired diagnostic/therapeutic isotopes (e.g., ⁶⁸Ga/¹⁷⁷Lu‑PSMA, ⁶⁴Cu/⁶⁷Cu)—enable personalized dosimetry and treatment monitoring.