โ๏ธIntro to Applied Nuclear Physics Unit 10 โ Nuclear Medicine & Medical Physics
Nuclear medicine harnesses radioactive isotopes for diagnosis and treatment, applying physics to medical practice. It involves understanding radioactivity, half-life, and activity measurements. Key concepts include absorbed dose, linear energy transfer, and various types of radioactive decay.
Medical imaging techniques like radiography, CT, PET, and MRI provide crucial diagnostic information. Radiation therapy, including external beam and brachytherapy, targets cancer cells. Dosimetry ensures safe radiation exposure, while emerging technologies like theranostics and radiomics shape the field's future.
Nuclear medicine utilizes radioactive isotopes for diagnostic imaging and therapeutic purposes
Involves the application of physics principles to medical diagnosis, treatment, and research
Radioactivity is the spontaneous emission of radiation from unstable atomic nuclei
Half-life (t1/2โ) represents the time required for half of a given quantity of a radioactive substance to decay
Activity (A) measures the rate of radioactive decay, expressed in becquerels (Bq) or curies (Ci)
1ย Bq=1ย decay/second
1ย Ci=3.7ร1010ย Bq
Absorbed dose quantifies the energy deposited by ionizing radiation per unit mass of matter, measured in grays (Gy)
Linear energy transfer (LET) describes the energy deposition rate along the path of ionizing radiation
Radioactive Decay and Isotopes
Radioactive decay occurs when an unstable atomic nucleus releases energy in the form of radiation
Alpha decay involves the emission of an alpha particle (two protons and two neutrons)
Beta decay involves the emission of a beta particle (electron or positron) and an antineutrino or neutrino
Gamma decay involves the emission of high-energy photons (gamma rays) from an excited nuclear state
Isotopes are variants of a chemical element with differing numbers of neutrons in their nuclei
Radioisotopes are unstable isotopes that undergo radioactive decay, emitting radiation
Common radioisotopes used in nuclear medicine include technetium-99m, iodine-131, and fluorine-18
Technetium-99m is widely used in bone scans and cardiac imaging
Iodine-131 is used for thyroid imaging and therapy
Fluorine-18 is used in positron emission tomography (PET) imaging
Radiation Detection and Measurement
Radiation detectors convert the energy of ionizing radiation into measurable electrical signals
Gas-filled detectors (ionization chambers, proportional counters, Geiger-Mรผller tubes) rely on the ionization of gas molecules by radiation
Scintillation detectors use materials that emit light when exposed to ionizing radiation, which is then converted to electrical signals by photomultiplier tubes
Semiconductor detectors (silicon, germanium) generate electron-hole pairs when exposed to radiation, producing an electrical signal
Thermoluminescent dosimeters (TLDs) measure accumulated radiation dose using materials that emit light when heated after exposure to radiation
Radiation spectrometry techniques (gamma spectroscopy, alpha spectroscopy) identify and quantify specific radionuclides based on their characteristic radiation energies
Counting statistics (background counts, efficiency, dead time) must be considered when interpreting radiation measurements
Medical Imaging Techniques
Radiography uses X-rays to produce two-dimensional images of internal structures
Computed tomography (CT) generates cross-sectional images by rotating an X-ray source and detector array around the patient
Single-photon emission computed tomography (SPECT) uses gamma-emitting radioisotopes to create three-dimensional images of functional processes
Positron emission tomography (PET) detects coincident gamma rays from the annihilation of positrons emitted by radioisotopes, providing functional and metabolic information
Magnetic resonance imaging (MRI) uses strong magnetic fields and radio waves to generate detailed images of soft tissues and organs
Ultrasound imaging employs high-frequency sound waves to visualize internal structures in real-time
Hybrid imaging techniques (PET/CT, SPECT/CT, PET/MRI) combine functional and anatomical information for improved diagnostic accuracy
Radiation Therapy Applications
Radiation therapy uses ionizing radiation to destroy cancer cells and shrink tumors
External beam radiation therapy (EBRT) delivers high-energy X-rays or particles from an external source
Linear accelerators (LINACs) generate high-energy X-rays or electrons for EBRT
Proton therapy uses proton beams to deliver precise radiation doses with reduced damage to surrounding tissues
Brachytherapy involves the placement of radioactive sources directly inside or near the tumor
Intracavitary brachytherapy (gynecological cancers) and interstitial brachytherapy (prostate cancer) are common applications
Radioisotope therapy uses targeted radionuclides to deliver therapeutic radiation doses to specific tissues or organs
Radioiodine therapy treats thyroid cancer and hyperthyroidism using iodine-131
Radium-223 is used for the treatment of bone metastases in prostate cancer patients
Treatment planning systems optimize radiation dose distribution to maximize tumor coverage while minimizing damage to healthy tissues
Dosimetry and Safety Protocols
Dosimetry is the measurement and calculation of radiation doses received by patients, workers, and the public
Equivalent dose (HTโ) accounts for the biological effectiveness of different types of radiation, measured in sieverts (Sv)
Effective dose (E) represents the whole-body dose that would result in the same stochastic risk as the sum of equivalent doses to individual organs
ALARA (As Low As Reasonably Achievable) principle guides radiation protection practices to minimize exposure
Occupational dose limits for radiation workers are set by regulatory agencies to prevent deterministic effects and limit stochastic risks
Personal protective equipment (lead aprons, thyroid shields, gloves) reduces radiation exposure to staff during procedures
Shielding materials (lead, concrete, tungsten) attenuate radiation and protect personnel and the public from unnecessary exposure
Quality assurance programs ensure the proper functioning and calibration of imaging and therapy equipment
Emerging Technologies and Future Trends
Theranostics combines diagnostic imaging and targeted radionuclide therapy using the same molecular target