Unsealed source radiotherapy
| Unsealed source radiotherapy | |
|---|---|
| Intervention | |
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| ICD-9-CM | 92.28 |
Unsealed source radiotherapy (also known as unsealed source radionuclide therapy (RNT) or molecular radiotherapy) uses solid, liquid, gaseous or other forms of radioactive substances called radiopharmaceuticals (essentially a radioactive drug). 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.
As such, 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.
Compare this with sealed-source therapy (brachytherapy) where the radionuclide remains in a capsule or metal wire during treatment, is never allowed to disperse within the body & hence needs to be physically placed precisely at the treatment position.
This is the most common RNT worldwide & uses the simple compound sodium iodide with the iodine-131 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.
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