TREINAMENTO INICIAL EM PROTEÇÃO RADIOLÓGICA - videoaula 01

Introduction to Radiological Protection in Nuclear Medicine

Overview of the Training

• The training is led by Daniel, a physicist specializing in medical physics and radiological protection at HC.

• The objective is to provide essential information for safe practice within the nuclear medicine sector.

Structure of Matter

• Discussion begins with the structure of matter, focusing on atoms as the fundamental building blocks of all visible matter.

• An atom is defined as the smallest division of an element that retains its chemical properties, consisting of protons, neutrons, and electrons.

Atomic Composition

• Protons have a positive charge, neutrons are neutral, and electrons carry a negative charge; in their neutral state, atoms balance these charges.

• The classical Bohr model represents atomic structure alongside a more modern quantum mechanical representation where electrons exist in probability clouds rather than fixed orbits.

Understanding Isotopes and Nuclides

Elements and Their Properties

• Elements are organized in the periodic table based on their number of protons (atomic number) and chemical properties.

• Each element can be characterized by its atomic number (number of protons) and mass number (sum of protons and neutrons).

Isotopes Explained

• Isotopes are variations of an element differing in neutron count; for example, iodine has 37 known isotopes.

• The term "nuclide" refers to any atomic species characterized by its proton and neutron numbers without specifying the elemental context.

Radioactivity: Concepts and Definitions

Radioactivity vs. Radiation

• Radioactivity involves unstable nuclei releasing energy to achieve stability; this process differs from general radiation which encompasses energy transfer via waves or particles.

Types of Radiation

• Common types include alpha, beta, and gamma radiation used in nuclear medicine applications.

Decay Processes in Radioactive Materials

Understanding Decay Rates

• Radioactive decay follows an exponential model where decay rate depends on original atom quantity and decay constant (λ).

Activity Measurement

• Activity quantifies how many atoms transform per unit time; measured in becquerels (Bq), with historical usage still favoring curies (Ci).

Half-Life Concept

Definition & Importance

• Half-life is defined as the time required for half the atoms in a sample to undergo transformation; it varies significantly among radionuclides.

Understanding Radioactive Decay and Radiation Types

The Concept of Half-Life

• The graph illustrates that after one half-life, a radioactive sample retains 50% of its original atoms; after two half-lives, it holds only 25%.

• Activity measures the quantity of a radioactive sample over time, while half-life is a constant characteristic for each isotope.

• For example, three samples of Technetium-99 with a half-life of 6 hours will show reduced quantities (5, 10, and 15 mCi) at different times.

Key Isotopes in Nuclear Medicine

• Fluorine-18 has a short half-life of just 2 hours and is used in PET scans.

• Iodine-131 has an eight-day half-life and is utilized for diagnosing thyroid conditions.

Sources of Radiation

• Radiation can be classified into natural and artificial sources; not all radiation types are equal based on their energy levels.

• Ionizing radiation can remove electrons from atoms or molecules, leading to ionization. Non-ionizing radiation does not have this capability.

Types of Ionizing Radiation

• Approximately 80% of human exposure to radiation comes from natural sources; only about 20% is from artificial sources like medical applications.

• There are three main types of ionizing radiation: alpha particles (massive with high ionization), beta particles (less massive), and gamma rays (electromagnetic with no mass).

Characteristics and Applications

• Alpha particles have low penetration power but high local ionization impact; gamma rays penetrate deeply but have lower local ionization effects.

• Gamma rays are preferred for diagnostic imaging due to their ability to pass through the body easily.

Detection Methods for Ionizing Radiation

Components of Radiation Detectors

• Detectors consist of two main components: a sensitive element that interacts with radiation and a conversion mechanism to read the signal generated.

Types of Detection Technologies

• Sensitive elements can be categorized into those based on ion collection (producing electric pulses when interacting with radiation).

Non-Ion Collection Detectors

• Non-ion collection detectors utilize various mechanisms such as bubble chambers or scintillation effects to detect particle trajectories or produce light signals.

Choosing the Right Detector

• The choice between detector types depends on the type of radiation being measured (particles vs. photons), as well as the intended purpose—whether it's imaging or quantifying activity.

Applications in Nuclear Medicine

• Various detectors serve distinct purposes in nuclear medicine, including activity measurement devices and specific types like Geiger-Müller counters.

Understanding Radiation Detection in Nuclear Medicine

Key Equipment and Their Functions

• The heart of nuclear medicine is the activity meter, a well-type detector crucial for measuring radioisotopes administered to patients. Proper selection of measurement windows is essential for accurate readings.

• When measuring Technetium-99m, it’s vital to ensure the device is configured correctly; incorrect settings can lead to erroneous measurements that compromise patient safety.

• The Geiger-Müller detector is commonly used to identify and measure radioactive contamination and dose rates from sources. However, it cannot differentiate between nuclides or radiation energies, providing only magnitude counts.

Imaging Techniques in Nuclear Medicine

• Diagnostic imaging equipment allows for mapping the biodistribution of radiopharmaceuticals within a patient's body. Images can be static, dynamic, or tomographic depending on the examination type.

• Using appropriate collimators and acquisition windows tailored to specific nuclides is critical for obtaining accurate diagnostic images.

Importance of Dosimeters

• Dosimeters are cumulative radiation detectors that estimate exposure over time. They must be worn during work hours in controlled areas but do not provide protection against radiation exposure themselves.

• Personal dosimeters should always be assigned individually and not shared. They help assess workplace conditions and validate protective measures' effectiveness.

Best Practices for Dosimeter Use

• Dosimeters should be stored properly when not in use—ideally on a designated board—to ensure accurate baseline radiation readings.

• If working across multiple sectors (e.g., tomography or hemodynamics), specific dosimeters must be used for each area without interchangeability to maintain precise monitoring of exposure levels.