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Radiotherapy can be applied from within the body too.
Radioactive medicine
A beta source, an isotope that emits beta radiation, is coupled to a certain chemical compound. This chemical would under normal circumstances be transported to a certain part of your body. You might know that iodine is added to table salt because your thyroid needs it. If somebody has a tumour in his thyroid gland, iodine-131 is given and his body transports the iodine to his thyroid gland. By choosing the right compound the radioactive medicine is transported by the body itself and deposited right next to the tumour.
Brachytherapy
You can also have some radiative material implanted surgically. With certain tumours, a lot of tiny tubes filled with radioactive material can be inserted. These tubes will remain there until the radioactive material is all used up. In the picture to the right, a person is being treated for prostate cancer in this manner, you can see the tubes on the x-ray.
This method only works if the dose doesn’t have to be that high.
Another option is to have hollow tubes inserted from the skin all the way into the tumour. During a session, a device (called an afterloader) pushed a thin flexible rod with radioactive material through the tube into the tumour. After a while, the machine retracts the tubes so the patient doesn’t have any radioactive material left in his body. After the last session, the tubes are removed again in surgery.
This method can be used when the dose has to be quite high so the patient has to be alone during a session.
Tracers
The fact that the body transports certain compounds to different parts of the body can also be used for imaging. A radioactive tracer is used to investigate a patient’s body without the need for invasive surgery. A small amount of radioactive material is put into the patient’s body and a radiographer puts a detector around the body to detect any gamma rays that pass out of the patient’s body. Depending on which system of the body needs to be investigated, the compound can be put in a drink or injected in the blood or muscles.
These diagnostics often use a gamma source because gamma radiation has a high penetration which means that most of the radiation will exit the body so it can be measured. To make sure the patient doesn’t stay radioactive for too long, a short-lived isotope is used. This also means that the hospital needs to be quite close to the production facility, you can’t stop or slow down the emission of radiation. This method is called a SPECT-scan, Single Photon Emission Computerised Tomography. The term more familiar to most is a CT-scan (cat-scan) but that is just a series of x-rays that “slice up” the body to get a better picture. The device to the top right is called as spect-ct scanner, by combining the two methods, the picture is even better.
A slightly newer technology is a PET-scan, Positron Emission Tomography. A radioactive isotope doesn’t produce an electron (so it’s not a beta source) but a positron, the antiparticle of the electron. When the positron hits an electron, which happens quite quickly, the annihilate each other. IN this annihilation, two gamma photons are produced that each travel in a different direction (by definition 180° apart) and those photons are detected by an imaging device. This device too is often combined with a CT-scanner (picture to the left). This device is mostly used to map the metabolism so the radioactive isotope is connected to a glucose molecule.
MRI-scan
To compete the story, an MRI (Magnetic Resonance Imaging) is a device that use magnetism and radio waves. An absolutely beautiful piece of technology but since it doesn’t use radioactive materials, not something for in this booklet.
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