Nuclear Medicinex

Nuclear Medicine Evolution of Nuclear Medicine • 1940s: Endocrinology: I-131 therapy and scan • 1950s: Thyroid, brain • 1970s: Renal, lung, bone, liver/spleen, Gallium • 1980s: Cardiology: Sestamibi SPECT scan • 1990s: Oncology, neurosciences: FDG-PET • 2000s: Hybrid Imaging: PET-CT and SPECT-CT • Emerging: molecular imaging, therapy, neuroscience SPECT: • Single photon emission CT • Rotation of camera 360° • Topographical display with improved spatial resolution • Applications in cardiac, brain, bone, liver/spleen, lung Clinical Applications Organ Radioisotope Pharmaceutical Energy (KeV) Half-Life Bone Tc-99m MDP 140 6 hrs Heart Tc-99m TI- SestaMibi 140 6 hrs 201 70 73 hrs Brain Tc-99m HMPAO 140 6 hrs Thyroid I-131 Hippuran 364 8 days Kidney I-131 Tc-99m Mag-3 364 8 days 140 6 hrs MAA 140 6 hrs (Gas) 71 62 hrs Citrate 90 78 hrs FDG 511 2 hrs Sulfur 140 6 hrs Lung Tc-99m Xe133 WB Oncology Ga-67 F-18 Liver Tc-99m Evaluate Diagnosis Method • Technical capacity • Diagnosis accuracy and impact • Therapeutic impact • Patient outcomes • Cost effectiveness Types of Ionising Radiation • X-ray o Extranuclearly produced (artificial) o Accelerate electrons, stop in a target, convert KE to X-ray (photon) • Gamma Radiation o Produced intranuclearly o Emitted by radioisotopes • Charged particles o Direct ionisation o α-particles, βparticles, protons, heavy ions • Neutrons o Indirect ionisation Dose of Absorbed Energy 𝑑𝐸 𝑑𝑀 • The mean energy imparted by ionising radiation • SI units: 1 Gray (Gy) = 1J/kg = 100cGy = 100rads = 1 Sievert (Sv) • Dose equivalent (H) o 𝐷𝑜𝑠𝑒 𝐸𝑞𝑢𝑖𝑣𝑎𝑙𝑒𝑛𝑡 "H" = Absorbed Dose "D" × Quality Factor (tissue) "Q" • Linear component (α) o Non-repairable damage to 2-strand DNA o Initial slop • Quadratic component (β) o Repairable damage to single strand DNA o Exponential component of curve • Early responding tissue o High α/β ratio o Main repair: cell repopulation • Late responding tissue o Low α/β ratio o Sub-lethal damage repair (SLDR) o Depends on dose per fraction, energy, oxygen, phases of cell cycle (G2/M) o Takes 4-6hrs Radiation Effects • Early: < 3 months o Loss of parenchymal cells in fast proliferating tissue o External beam therapy o Radioisotope therapy: iodine, strontium, samarium o Deterministic effect: mucositis, dermatitis, bone marrow • Late: > 3 months o Main mechanism: vascular occlusion  ischaemia: slow proliferating o Deterministic effect: due to cell killing e.g. cataracts, lung fibrosis, bone necrosis o Stochastic effect: random DNA damage  NOT dose dependent  Carcinogenesis, genetic mutations Radiation Exposure Doses • ALARA principle • Gallium, thallium: 20mSv • Sestamibi, FDG, renal, bone, brain: 2-10mSv • Lung: <2mSv • CTPA: 25mGy for breasts  14% increased risk of breast cancer Thyroid Scan • Free technetium • Quantitation of tracer uptake into thyroid o Absolute or relative to uptake in thigh • Contraindications: iodine contrast, amiodarone, thyroxine, thionamides • Grave’s disease: diffuse increase tracer uptake • Thyroiditis: diffuse decrease tracer uptake • Toxic solitary adenoma • Toxic multinodular goitre • Cold nodule: solitary nodule, some malignant • Hot nodule: functioning thyroid adenomas • Intermediate nodule: FNAB indicated Bone Scan • Technetium phosphate analogues  3 phase imaging: o Dynamic and blood pool phase  5-10 minutes post injection o Delayed phase  2-3 hours post injection  Osteoblastic activity Cardiac Imaging • Structure and function: ECHO, MRI • Perfusion: nuclear, MRI • Lumen assessment to quantify stenosis: CT, MRI • Plaque characterisation: CT, MRI, molecular imaging, hybrid • Prognosis: hybrid, nuclear