physics

Radionuclide therapy

Radionuclide therapy is a physics topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Radionuclide therapy rather than just read about it. In short: Radionuclide therapy (RNT, also known as unsealed source radiotherapy or molecular radiotherapy) uses radioactive substances called radiopharmaceuticals to treat medical conditions, particularly cancer. These are introduced into the body by various means (injection or ingestion are the two most commonplace) and localise to specific locations, organs or tissues depending on their properties and administration routes.

Key takeaways

Radionuclide therapy belongs to physics; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Radionuclide therapy to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Radionuclide therapy from memory before moving on to harder problems.

Reference excerpt

Radionuclide therapy (RNT, also known as unsealed source radiotherapy or molecular radiotherapy) uses radioactive substances called radiopharmaceuticals to treat medical conditions, particularly cancer. These are introduced into the body by various means (injection or ingestion are the two most commonplace) and localise to specific locations, organs or tissues depending on their properties and administration routes. This includes anything from a simple compound such as sodium iodide that locates to the thyroid via trapping the iodide ion, to complex biopharmaceuticals such as recombinant antibodies which are attached to radionuclides and seek out specific antigens on cell surfaces. This is a type of targeted therapy which uses the physical, chemical and biological properties of the radiopharmaceutical to target areas of the body for radiation treatment. The related diagnostic modality of nuclear medicine employs the same principles but uses different types or quantities of radiopharmaceuticals in order to image or analyse functional systems within the patient. RNT contrasts with sealed-source therapy (brachytherapy) where the radionuclide remains in a capsule or metal wire during treatment and needs to be physically placed precisely at the treatment position. When the radionuclides are ligands (such as with Lutathera and Pluvicto), the technique is also known as radioligand therapy.

Clinical use

Thyroid conditions

Iodine-131 (131I) is the most common RNT worldwide and uses the simple compound sodium iodide with a radioactive isotope of iodine. The patient (human or animal) may ingest an oral solid or liquid amount or receive an intravenous injection of a solution of the compound. The iodide ion is selectively taken up by the thyroid gland. Both benign conditions like thyrotoxicosis and certain malignant conditions like papillary thyroid cancer can be treated with the radiation emitted by radioiodine. Iodine-131 produces beta and gamma radiation. The beta radiation released damages both normal thyroid tissue and any thyroid cancer that behaves like normal thyroid in taking up iodine, so providing the therapeutic effect, whilst most of the gamma radiation escapes the patient's body. Most of the iodine not taken up by thyroid tissue is excreted through the kidneys into the urine. After radioiodine treatment the urine will be radioactive or 'hot', and the patients themselves will also emit gamma radiation. Depending on the amount of radioactivity administered, it can take several days for the radioactivity to reduce to the point where the patient does not pose a radiation hazard to bystanders. Patients are often treated as inpatients and there are international guidelines, as well as legislation in many countries, which govern the point at which they may return home.

Bone metastasis

Radium-223 chloride, strontium-89 chloride and samarium-153 EDTMP are used to treat secondary cancer in the bones. Radium and strontium mimic calcium in the body. Samarium is bound to tetraphosphate EDTMP, phosphates are taken up by osteoblastic (bone forming) repairs that occur adjacent to some metastatic lesions.

Bone marrow conditions Beta emitting phosphorus-32 (32P), as sodium phosphate, is used to treat overactive bone marrow, in which it is otherwise naturally metabolised.

Joint inflammation

Yttrium-90 colloid An yttrium-90 (90Y) colloidal suspension is used for radiosynovectomy in the knee joint.

Liver tumours

Yttrium-90 spheres

90Y in the form of a resin or glass spheres can be used to treat primary and metastatic liver cancers.

Neuroendocrine tumours

Iodine-131 mIBG 131I-mIBG (metaiodobenzylguanidine) is used for the treatment of phaeochromocytoma and neuroblastoma.

Lutetium-177

177Lu is bound with a DOTA chelator to target neuroendocrine tumours.

Experimental antibody based methods At the Institute for Transuranium Elements (ITU) work is being done on alpha-immunotherapy, this is an experimental method where antibodies bearing alpha isotopes are used. Bismuth-213 is one of the isotopes which has been used. This is made by the alpha decay of actinium-225. The generation of one short-lived isotope from longer lived isotope is a useful method of providing a portable supply of a short-lived isotope. This is similar to the generation of technetium-99m by a technetium generator. The actinium-225 is made by the irradiation of radium-226 with a cyclotron.

References

Worked examples

Example 1 — a first encounter with Radionuclide therapy

Start with the simplest possible case. Write down what Radionuclide therapy claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In physics, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Radionuclide therapy before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Radionuclide therapy ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Radionuclide therapy

In research: Radionuclide therapy appears in physics research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Radionuclide therapy in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Radionuclide therapy is common in secondary-school and first-year university syllabi. It links to neighbouring topics Nuclear medicine, Radiation therapy, so understanding it makes those chapters shorter.
In everyday life: Look for Radionuclide therapy outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Radionuclide therapy in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Radionuclide therapy means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Radionuclide therapy out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Radionuclide therapy in simple terms?

Why does Radionuclide therapy matter?

Because it connects several physics ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Radionuclide therapy?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Radionuclide therapy.