Radiation Physics: Radioactivity and Interaction

Basic Radiation Physics

• Atomic structure includes the atomic number and mass number.
• Isotopes and radioisotopes exhibit radioactivity and specific activity.
• Alpha, beta, and gamma rays possess general properties and follow laws of radioactivity alongside successive transformations.
• Key concepts include half-life, decay constant, and mean life within natural radioactive series and radioactive equilibrium.
• Artificial radioactivity is achieved through neutron and charged particle bombardments, influencing nuclear cross-sections.

Interaction of Radiation with Matter

• Charged particles interact with matter through energy transfer mechanisms, scattering, excitation, and ionization.
• The Bragg curve illustrates the correlation between range and energy, including stopping power, bremsstrahlung, and the behavior of heavy charged particles.
• Specific ionization is a notable characteristic.
• X- and gamma rays interact with matter through the photoelectric effect, Compton scattering, and pair production.
• Exponential attenuation, modes of interactions, attenuation and mass energy absorption coefficients are important.
• Shielding materials are used for buildup correction.
• Neutrons interact with matter via scattering and absorption.
• Neutron-induced nuclear reactions and radioactive capture reactions, such as (n, p) and (n, ), occur, followed by moderation using shielding materials.

Basic X-ray Physics

• X-ray production and properties, along with characteristics and continuous spectra are vital.
• Medical diagnostic and therapeutic tubes have basic requirements.
• Safety devices are included in X-ray tubes, and modern X-ray tubes use specific technology.
• Insulation and cooling of X-ray tubes is key.
• Filtration and beam quality are controlled in mobile and dental units.
• Malfunctions of X-ray tubes, loading limitations, control panels, and image intensifiers are all important.
• Electron accelerators also use specific technology.

Radiation Quantities and Units

• Particle flux and fluence, as well as energy flux and fluence, are key measurements.
• Cross section is used with energy, and linear energy transfer (LET) is important.
• Important factors; mass attenuation coefficient, mass stopping power, w-value, exposure (rate), Kerma (rate), and Terma.
• Absorbed dose (rate), activity, and energy are meausred.
• Other key measurements; charged particle equilibrium (CPE), radiation weighting factors, tissue weighting factors, equivalent dose, effective dose, and collective effective dose.
• Annual Limit of Intake (ALI) and Derived Air Concentration (DAC) are crucial.
• Personnel dose equivalent and committed dose are also important.

Radiation Dosimetry

• Absorbed dose, Kerma, exposure, activity, and rate constants are measured.
• The Charged Particle Equilibrium (CPE) and the relationship between Kerma, absorbed dose, and exposure under CPE are important.
• Exposure and air kerma are determined using ionization chambers for low, medium, and high energy X-rays and gamma rays.
• Dosimetry is determined using ionization chambers, films, and Thermoluminescence Dosimeters (TLDs).
• Bragg-Gray cavity principle and Burlin and Spencer-Attix cavity theories are applied.
• Calorimeters and chemical dosimeters are used.
• Beam and source dosimetry methods include point source/line source/cylindrical source techniques.
• This involves neutron dosimetry and consistency checks of dosimeters.

Principles of Radiation Detection

• Basic principles of radiation detection in gas-filled detectors, ionization chambers (theory and design), construction of condenser type chambers, and thimble chambers.
• Other key measurements; gas multiplication, proportional and GM counters, characteristics of organic and inorganic counters, dead time and recovery time.
• Solid-state detectors include; scintillation detectors, semiconductor detectors, chemical systems, radiographic films, and radiochromic films.
• Thermoluminescent Dosimeters (TLD), Optically stimulated Luminescence dosimeters (OSLD), radiophotoluminescent dosimeters, neutron detectors, nuclear track emulsions for fast neutrons, and solid-state nuclear track (SSNTD) detectors, calorimeters.

Radiation Measuring & Monitoring Instruments

• Dosimeters are based on condenser chambers and pocket chambers and use current measurement.
• Electrometers include MOSFET, vibrating condenser, and Varactor bridge types.
• Devices are used as secondary standard therapy level dosimeters, farmer dosimeters, radiation field analyzers (RFA), radioisotope calibrators, multipurpose dosimeters, water phantom dosimetry systems, and brachytherapy dosimeters.
• Thermoluminescent dosimeter readers calibrate and maintain dosimeters for medical applications.
• Instruments for personnel monitoring include TLD badge readers, glass dosimeter readers and digital pocket dosimeters using solid-state devices and GM counters.
• Other instruments; teletectors, industrial gamma radiography survey meters, gamma area (zone) alarm monitors, contamination monitors for alpha, beta, and gamma radiation, hand and foot monitors, laundry and portal monitors, and scintillation monitors for X-ray and gamma radiations.
• Neutron monitors, tissue equivalent survey meters, flux meters, dose equivalent monitors, pocket neutron monitors, and teledose systems.
• Instruments for counting and spectrometry; portable counting systems for alpha and beta radiation, gamma ray spectrometers, multichannel analyzers, liquid scintillation counting systems, RIA counters, which perform whole body counts, and air monitors for radioactive particulates and gases.

Radiation Biology

• Radiation interacts with cells, leading to chromosome aberrations, mutations, and potentially lethal/sub-lethal damage.
• Modification of radiation damage occurs through LET (linear energy transfer), RBE (relative biological effectiveness), dose rate, and dose fractionation.
• Stochastic and deterministic effects, acute radiation sickness, and LD50/60 are noted.
• Radiation impacts skin, blood-forming organs, the digestive tract, and the reproductive system.
• The genetic effects of radiation, and physical/biological factors affect cell survival.
• Chemical and hyperthermic sensitizers, radio-protectors, and tumor biology are crucial.
• Fractionation schemes, high LET radiation therapy, and the radiobiological basis of radiotherapy are important.
• Time dose fractionation (TDF), gap correction, and the linear quadratic model are key.

Diagnostic Radiology

• X-ray diagnosis relies on physical principles, density, contrast, detail, and definition of radiographs along with kV, mAs, and filtration.
• FSD, screens, films, grids, and contrast media are used.
• Radiography, myelography, tomography, fluoroscopy, pelvimetry, and stereoscopy are key.
• Film processing and image intensifiers are utilized.
• Optimization of patient dose and guidance levels are considered.
• CT scanners, digital subtraction angiography (DSA), mammography, bone densitometry, dental radiography, interventional radiology, and digital radiology are crucial.
• Performance standards, acceptance criteria, and quality assurance (QA) are required for diagnostic equipment.

Nuclear Medicine

• Clinical radioisotope laboratories use open isotopes, including 99Tc, in functional studies.
• Measuring radioactivity is essential, considering collimator design and using whole body counters.
• Physical principles of isotope dilution analysis and circulation time are important.
• Radioisotope scanners and cameras are used.
• Cyclotron-produced radionuclides, SPECT, PET, and radio-immunoassay (RIA) are used; 131I therapy is employed.
• Patient dose is monitored alongside guidance levels, protection principles, and decontamination procedures.
• Performance standards, acceptance criteria, and quality assurance (QA) in nuclear medicine equipment are required.

Radiotherapy

• Benign and malignant tumors are treated using palliative therapy and curative therapy.
• Beam therapy equipment includes kV X-ray machine, telecobalt units, and medical electron linear accelerators.
• Output calibration procedures are used for photon and electron beams.
• Dosimetry parameters and patient dose calculations are performed.
• Neutron capture therapy, proton therapy, and heavy-ion therapy are employed.
• Radioisotopes are used in brachytherapy, including LDR, MDR, HDR, and PDR.
• Remote afterloading brachytherapy units are utilized.
• Source strength is measured, and integrity checks are performed for sources.
• Treatment planning systems (TPS) are used in radiotherapy, including IMRT/IGRT - with occupational safety measures.
• Performance standards, acceptance criteria, and quality assurance (QA) are implemented in radiotherapy equipment.

Radiation Protection Standards

• Radiation dose to individuals from natural radioactivity in the environment and man-made sources exists.
• Concepts of radiation protection standards, International Commission on Radiological Protection (ICRP) and its recommendations are important.
• Categories of exposures, risk factors, and international/national radiation protection standards like ICRP, BSS, and AERB are considered.
• There is an overview of UNSCEAR recommendations.
• Factors governing internal exposures are addressed.
• There are radionuclide concentrations in air and water, and contamination levels.
• Dose limits are set for occupational workers, the general public, comforters, and trainees.

Radiation Hazard Evaluation and Control

• Radiation hazards, both internal and external, need evaluation and control.
• Both individual and workplace monitoring must be maintained.
• Shielding calculations and planning of medical radiation installations are performed.
• Shielding parameters; workload (W), use factor (U), and occupancy factor (T).
• Primary and secondary protective barriers are designed.
• There are shielding requirements for diagnostic X-ray facilities, telecobalt, medical accelerator, brachytherapy installations, and medical radioisotope laboratories.
• Radiation monitoring instruments are calibrated and monitored.
• Radiation monitoring procedures are used for radiation-generating equipment and facilities.
• Protective measures reduce radiation exposure to patients and occupational workers.
• Radiation hazards are present in radioisotope laboratories.

Disposal of Radioactive Waste

• The sources of radioactive waste and its classification is important.
• Treatment techniques are employed for solid, liquid, and gaseous effluents.
• Permissible limits for disposal of waste are enforced, and sampling techniques are used for air, water, and solids.
• Geological, hydrological, media meteorological, and ecological factors for waste disposal are considered.
• Decontamination procedures are performed.
• Measures for disposal of radioactive wastes in medical, industrial, agricultural, and research facilities.

Transport of Radioactive Material

• Regulatory aspects of transport of radioactive material (RAM), introduction, terms used (e.g. Competent Authority, A1 & A2 values, unilateral & multilateral approvals, special form radioactive material, special arrangement, transport index (TI) etc.).
• The transport scenarios (routine, normal and accidental) and variety of packages covered under the transport regulations (including designing, testing, transport and storage).
• General requirements of all packaging, requirements for transport by air mode, test requirements.
• Preparation, marking, labeling of packages, preparation of transport documents (consignors declaration, TREM Card, instructions to the carrier & emergency preparedness in writing), responsibilities of consignor, general instructions and response to off-normal situations during transport.

Regulatory Aspects for Medical Radiation Facilities

• National legislation and regulatory framework, is employed.
• Regulatory documents such as Acts, Rules, safety codes, standards, guides, and manuals, along with radiation surveillance procedures and regulatory controls.
• Responsibilities of the employer, licensee, Radiological Safety Officer (RSO), technologist, radiation workers, and radioisotope supplier are important.
• Regulations regarding physical protection, safety and security of sources during storage, handling and disposal.
• Regulatory requirements for import/export, procurement, handling, transfer and disposal of radioisotopes are followed.
• Inventory control and security provisions; security threat and graded approach in security provision with a Radiation Protection Programme (RPP), is conducted.

Radiation Emergencies and Medical Management

• Dealing with radiation accidents and emergencies involving radiation sources and equipment and maintaining radiation safety
• Implement safety measures during source transfer operations, source stuck handling procedures.
• Protocols for tracing and recovering lost sources are created.
• Case studies and lessons learned from past radiation injuries should be studied.

Emergency Response Plans and Preparedness

• Planning and preparedness are required, including notification and communication procedures.
• Administrative and technical procedures, and emergency response accessories will be on hand.
• Responsibilities of the employer, licensee, RSO, technologist, radiation workers, and radioisotope/equipment supplier must be defined in case of emergency.