Radioactivity Revision Notes

External Beam Radiation Therapy (EBRT)

EBRT delivers radiation from a machine outside the body. It uses high-energy X-rays or protons directed at the tumour. This method is non-invasive and can treat large areas or tumours that are deep within the body. The radiation passes through healthy tissue to reach the tumour, so clinicians carefully plan the beam angles and intensity to reduce exposure to non-cancerous cells. Treatment usually occurs over several sessions.

Internal Radiation Therapy (Brachytherapy)

Brachytherapy involves placing a radioactive source directly into or very near the tumour. This allows for a very high dose of radiation to be delivered to a small, localised area, while rapidly decreasing the dose to surrounding healthy tissues. Brachytherapy can be temporary (e.g., in a catheter) or permanent (e.g., radioactive seeds). It is often used for cancers like prostate, cervical, and breast cancer. The advantage is highly targeted delivery, but it requires invasive procedures for placement.

Comparison and Contrast

Both external and internal radiation therapies aim to destroy cancer cells. External therapy is non-invasive, treats larger areas, and radiation passes through healthy tissue. Internal therapy is invasive, delivers a high, localised dose, and minimises exposure to distant healthy tissue. External therapy offers flexibility in targeting, while internal therapy provides precision due to direct contact with the tumour. Side effects vary based on the method and location treated, but both can cause fatigue and skin changes, local to the radiation site.

Radioactive Tracers in Medical Diagnosis

Radioactive tracers are substances containing unstable isotopes that emit radiation. When introduced into the body, they allow medical professionals to observe the function or structure of organs. Gamma emitters are often preferred because gamma radiation can easily pass through the body to be detected externally, allowing for imaging without significant internal dose. The chemical properties of the tracer determine where it goes in the body, such as tracking blood flow or metabolic activity in specific organs. Tracers must have a relatively short half-life to minimise patient exposure to radiation while still allowing enough time for diagnosis.

PET Scanners and Positron Emission Tomography

PET scanners use radioactive tracers that emit positrons. When a positron from the tracer encounters an electron in the body's tissues, an annihilation event occurs. This event produces two gamma photons that are emitted in opposite directions (180 degrees apart). A ring of detectors encircles the patient and simultaneously detects these paired gamma photons. A computer then processes these detection events to construct detailed three-dimensional images of organs and their metabolic activity. PET scans are particularly useful for detecting and monitoring cancers, heart disease, and neurological disorders.

Properties of Ideal Radioactive Tracers

For medical diagnostic use, radioactive tracers should possess specific characteristics. They should emit gamma radiation for effective penetration through tissue and detection, while minimising damage. The isotope chosen should have a short half-life, ideally minutes to a few hours, so that it decays quickly after the imaging is complete, reducing the patient's radiation dose. The tracer must also be chemically suitable for uptake by the specific organ or tissue being studied, ensuring it targets the correct area to provide useful diagnostic information.

What are PET scanners?

PET (Positron Emission Tomography) scanners are medical imaging devices that use radioactive tracers to visualise and measure metabolic processes in the body. They are particularly useful for detecting diseases like cancer, heart conditions, and brain disorders by showing how organs and tissues are working.

Importance of Isotopes in PET

PET scanners rely on radioactive isotopes that emit positrons. When a positron encounters an electron in the body, they annihilate, producing two gamma rays that travel in opposite directions. These gamma rays are detected by the scanner, allowing for the creation of detailed 3D images of internal body function. Common isotopes include Fluorine-18 and Carbon-11.

Why Nearby Production is Essential

Isotopes used in PET scanning typically have short half-lives, meaning their radioactivity decreases rapidly. For example, Fluorine-18 has a half-life of about 110 minutes, and Carbon-11 has a half-life of about 20 minutes. If these isotopes were transported over long distances, too much of their radioactivity would decay, leaving insufficient material for effective diagnosis. Therefore, they must be produced in specialised facilities (cyclotrons) located in close proximity to the medical centres where they will be administered.

Impact of Short Half-Life on Dosage

The short half-life directly affects the available dose for the patient. Even a few hours of transport can significantly reduce the amount of active isotope. Producing them nearby ensures that a high enough concentration of the isotope is administered to provide clear and accurate imaging, without needing to produce an excessively large initial quantity.

Benefits of Nuclear Power

Nuclear power plants do not emit carbon dioxide or other greenhouse gases during their operation, playing an important role in cutting emissions that drive climate change. They supply consistent, reliable electricity—known as baseload power—and have a high energy yield from a small amount of fuel, supporting energy security and reducing reliance on fossil fuels.

Limitations and Challenges

Key limitations include the creation of radioactive waste that must be securely stored for thousands of years to prevent environmental harm. Nuclear plants are costly and take significant time to build, and public perceptions of nuclear power are shaped by safety concerns and the severity of rare but serious accidents. This can affect public acceptance and government support for nuclear projects.