Medical uses (AQA GCSE Physics): Revision Notes
Medical uses
Nuclear radiation has important uses in medicine. It helps doctors explore organs inside the body and treat unwanted tissue like cancer.
Medical tracers
Medical tracers are special substances that contain radioactive isotopes. Doctors use them to monitor what happens inside a patient's body.
Properties of medical tracers
Medical tracers have specific features that make them useful:
- Absorbed by the body: They are isotopes of elements or parts of compounds that the body naturally takes in
- Gamma ray emitters: They usually give off gamma rays, which can be detected from outside the body
- Right half-life: Long enough to create a useful image, but short enough so the radioactive nuclei mostly decay after the scan is complete
The half-life of medical tracers is carefully chosen to balance image quality with patient safety. Too long, and the patient receives unnecessary radiation exposure. Too short, and there isn't enough time to capture useful diagnostic information.
How medical tracers work
Patients can eat or drink the tracer substance, or doctors can inject it into their body. The radioactive tracer travels through the body and takes part in normal biological processes.
The ionising radiation from the tracer can be detected by special equipment outside the body. This allows doctors to see exactly where the tracer has gone and diagnose health problems.
Medical Tracer Example: FDG Imaging
FDG (fluorodeoxyglucose) is a radioactive form of glucose. It travels in the blood to tissues that use glucose for energy. When parts of the brain are affected by disease, they use less glucose, so less radioactivity is detected in those areas. This helps doctors identify damaged or diseased brain tissue.
Destroying unwanted tissue internally
Cancer tumours can be treated by putting radioactive sources inside the patient's body.
Methods of internal treatment
There are two main ways to get radioactive material inside a patient:
- Injection: The radioisotope is injected directly into the patient
- Ingestion: The patient eats or drinks something containing the radioisotope
How internal treatment works
Radioactive implants destroy cancer cells in tumours. Beta or gamma-emitting isotopes are used as small seeds or tiny rods placed near the cancer.
The isotopes are chosen with half-lives long enough to treat the tumour over time, but short enough to limit the radiation dose to the patient.
The careful selection of isotopes with appropriate half-lives is crucial for patient safety. The radiation must be strong enough to destroy cancer cells but not so persistent that it causes long-term harm to healthy tissue.
Internal Treatment Example: Iodine-131 for Thyroid Cancer
Iodine-131 treats thyroid cancer. Patients swallow it in a capsule. The iodine is absorbed by the thyroid gland but not by other parts of the body. This means the ionising radiation destroys thyroid cancer cells without harming healthy cells nearby.
Destroying unwanted tissue externally
External treatment uses gamma rays from outside the body to target cancer.
How external treatment works
Several beams of gamma rays are aimed at the cancer from different positions around the patient. Each individual beam is not strong enough to kill the tumour, but it damages it slightly.
By moving the beam position, the amount of ionising radiation received by healthy tissue around the tumour is reduced. The cancer receives the full dose from all beam positions.
This technique, called radiotherapy, allows doctors to deliver a concentrated dose of radiation to the tumour while minimising exposure to surrounding healthy tissue. The multiple beam approach is key to this precision.
Why gamma rays are used
Gamma rays are chosen for external treatment because they can penetrate deeper into the body than alpha and beta particles from an external source.
Key Points to Remember:
- Medical tracers contain radioisotopes that help doctors see inside the body without surgery
- Internal treatment puts radioactive material inside patients to destroy cancer from within
- External treatment uses multiple gamma-ray beams from outside the body to target cancer
- FDG follows glucose in the body and shows which tissues are using energy
- Iodine-131 specifically targets the thyroid gland to treat thyroid cancer