Learning Outcomes
LO 1: Understand atomic structure
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AC 1.1: Describe the fundamental differences between protons, neutrons and electrons in terms of mass and charge
LO 2: Understand the nature of alpha, beta and gamma radiation, and x-rays
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AC 2.1: Explain how the range in air and penetrating powers of alpha, beta, gamma and x-rays are related to their nature and properties
AC 2.2: Explain the safety procedures followed when using alpha, beta and gamma radiation and x-rays
LO 3: Understand the main uses of ionising radiation in monitoring and treatment
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AC 3.1: Explain the use of the Barium meal for soft body imaging
AC 3.2: Explain the use of γ-rays in imaging
AC 3.3: Explain the use of internal sources of radiation in treatment procedures
LO 4: Understand how radio isotopes are used in health care
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AC 4.1: Explain how technetium-99m is generated
AC 4.2: Explain the use of Iodine-131 in thyroid investigations
LO 5: Understand the health applications of a selected part of electromagnetic spectrum
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AC 5.1: Explain medical uses of parts of the electromagnetic spectrum
LO 6: Understand how ultrasound is used in health care
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AC 6.1: Explain the use of ultrasonics in medical imaging and treatment
3.1: Explain the use of the barium meal for soft body imaging
Lesson 5 of 11
The use of ionising radiation in medicine includes both monitoring and treatment of patients and falls into two broad categories; radiography and radiotherapy. Radiography involves the production of an image to monitor or diagnose medical conditions (‘graph’ = from the Greek ‘to draw’ or ‘describe’), whereas radiotherapy involves some form of treatment of a disorder (‘therapeia’ = Greek for ‘healing’).
Radiotherapy
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Radiotherapy uses ionising radiation to destroy cancer cells, and around 40% of people diagnosed with cancer will have it as part of their treatment. It can also be used before surgery to shrink a tumour so it’s easier to remove, or after surgery to kill off any cancer cells that survived the operation.
As an external process, high energy x-rays are focussed onto the patient in a very specific target area. The radiation damages cancer cells, causing them to die or stop growing. Healthy cells nearby are also damaged, but these are usually able to repair themselves and recover.
The patient needs to be positioned very carefully on the table of the machine to ensure that only the affected area is treated with the radiation beam.
Radiotherapy may also be delivered to a patient internally, using radioactive liquids and implants to attack cancerous cells more directly. Implants maybe wires and tubes placed in the patient to release radiation near cancer cells, then left in the body for a period of time from a few minutes to maybe days, or sometimes permanently.
3.2: Explain the use of γ-rays in imaging
Lesson 6 of 11
We learnt earlier in this unit that x-rays are produced by controlled electron bombardment in an appropriately designed machine. Gamma rays are very similar to x-rays but are produced by radioactive decay inside the nucleus of an atom.
If it helps to think of the radioactive nucleus as a tiny x-ray machine, you may start to appreciate how useful this may be. Radioactive nuclei can be attached to substances that can be put into the human body, which then produce detectable radiation from wherever those substances end up. These radioactive ‘tracers’ can be delivered into the body, by injection, ingestion, or inhalation, and by choosing appropriate radionuclides and carrier molecules the tracers can be targeted to specific body systems, specific organs, or even specific types of cell.
Whereas x-rays are useful is providing us with an image of the body’s anatomy, i.e. what it looks like, gamma ray imaging provides us with a means to visualise what the body is doing. It provides a ‘functional’ image of the processes taking place in particular organs or development of tissues and bones.
Radioactive liquids to treat cancer are given either as a drink or by injection. Examples include:
⦁ Radioactive phosphorus – used for blood disorders
⦁ Radioactive radium – used for cancer that has spread to the bones
⦁ Radioactive strontium – used for secondary bone cancers
⦁ Radioactive iodine – used for benign thyroid conditions and thyroid cancer.
As with the radioactive tracers used in PET scans described earlier, the radioactive part of the liquid may be attached to another substance, which is designed to take the isotope into the tumour.
Radioactive implants
Internal radiotherapy implants are radioactive metal wires, seeds, or tubes put into your body, inside or close to a tumour. In temporary brachytherapy, a highly radioactive material is placed inside a catheter or slender tube for a specific amount of time – often just a few minutes, sometimes a few days – and then withdrawn. The radiation dose is determined by the activity of the radioisotope and the duration of the treatment.
In some types of cancer, small metal implants, or seeds, are left in the body permanently – this is known as permanent brachytherapy. These implants may be made of radioactive gold or contain radioactive iodine or another appropriate radioisotope. They give a very high dose of radiation to the area of the cancer cells. The radiation dose in this case is determined by the activity of the radioisotope and its half-life (see below).
4.1: Explain how technetium-99m is generated
Lesson 8 of 11
Sources of radiation that are administered to humans internally have to be chosen carefully. By injection, ingestion or inhalation, a patient is given a low dosage radioisotope that is targeted to reach a specific organ. The radioisotope needs to produce radioactive emissions of sufficient strength to impact the organ to be treated, or to be detected by the sensors. We do not want to cause danger to the patient’s health, however, by prolonging their exposure to the radiation longer than is necessary.
Isotopes
As we discovered earlier, the number of protons in an atom determines what element it is, e.g.
One proton = hydrogen
Two protons = helium
Six protons = carbon
79 protons = gold
…and so on.
Different number of protons = Different element
If the number of protons in the nucleus changes, it becomes a different element. But if the number of neutrons changes, we have the same element but with a greater or lesser atomic mass, and which is potentially unstable.
An isotope is an atom with the same number of protons, but a different number of neutrons. For example, the most common form of Hydrogen has just one proton and a single orbiting electron. If it had an extra proton it would become Helium, a different element. But if it has an extra neutron or more, it just gains mass and becomes more unstable. If an atom is unstable, it is likely to break down and emit radiation. This is radioactive decay.
Barium sulphate, as used in a ‘barium meal’ procedure described earlier, has a half-life of only 10 days. That means that after 10 days half the radioactive atoms have decayed; and after 50 days (five half-lives) 90% of the radioactive atoms have decayed to a stable product. Though in fact most of it will have been removed from the body by ‘natural biological functions’.
By contrast, carbon-14, as used in ‘carbon dating’ processes, has a radioactive half-life of around 5700 years. That means that something excavated from the Bronze Age, circa 3300BC, will contain around half the number of carbon-14 atoms that it had when it was buried.
Technetium-99m is a radioactive tracer that is used in twenty million medical diagnostic procedures per year. It is used for imaging and studying organs such as the brain, heart muscle, thyroid, lungs, liver, gallbladder and kidneys, as well as the skeleton and blood and for the investigation of tumours.
It does not occur naturally, so let’s have a look at its ancestral line of isotopes.
6.1: Explain the use of ultrasonics in medical imaging and treatment
Lesson 11 of 11
What is a sound wave?
A sound wave is a sequence of vibrations in the air or other medium. They are ‘pulses’ that travel through materials as the particles are compressed together and stretched apart. The vibrations travel through air at a speed of 340 metres per second; in solids the vibrations travel much faster. At higher altitudes, where the air is thinner and the molecules are spaced further apart, sound travels much slower. In a vacuum (like space), sound cannot travel through at all. This is because there are no molecules to transfer the vibrations.
Piezoelectric crystals vibrate in response to an alternating voltage, and when placed against a patient’s skin and driven at high frequencies produce ultrasound pulses that travel through the body. As they travel outwards and encounter different layers within the body the ultrasound waves are reflected back towards the source.
The returning signal drives the crystals in reverse and produces an electronic signal that is processed to construct the image.
Here’s a ‘60 seconds of science’ explanation that covers the ultrasound scanner.
Applications of ultrasound imaging
Ultrasound is used to help physicians investigate symptoms such as pain, swelling and infection, and can help to diagnose a variety of conditions in most of the organs of the body including the heart and blood vessels, the liver, kidneys, brain, and eyes. Ultrasound of the heart is commonly called an “echocardiogram” or “echo” for short. It can scan for abnormalities and tumours in the breasts, testicles, and thyroid. It is frequently used to scan the foetus in pregnant patients, and to examine the hips and spine in young infants.
Ultrasound is also used to guide procedures such as needle biopsies, in which needles are used to sample cells from an abnormal area for laboratory testing, and to guide radiotherapy implants such as used to treat prostate cancer.
A variation on the standard ultrasound scan is ‘Doppler ultrasound’, which can provide important information on blood flow.
To study the health effects of Hanford's iodine-131, researchers investigated a group of people with a wide range of radiation doses to the thyroid. In this way, researchers could compare groups of people with similar characteristics (such as lifestyle and diet) but different levels of exposure.
Other studies suggest that young children may be the most susceptible to the effects of radiation on the thyroid gland. Therefore, the HTDS selected participants who were young children when Hanford releases of iodine-131 were highest. Scientists also ensured that the HTDS participants included many people who lived in areas around Hanford where the highest thyroid radiation doses occurred.
From a sampling of 5,199 birth records, scientists were able to locate 3,440 people who were both willing to participate and able to provide the necessary data for evaluation of thyroid disease.
Participants underwent complete evaluations for thyroid disease, and provided detailed information about the places they lived and the quantities and sources of the food and milk they consumed.
For each type of thyroid disease, the research team examined how the rates of disease varied in relation to participants' estimated radiation doses from Hanford's iodine-131.
