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Physics and the Cosmos Physics and the Cosmos The atomic nucleus Medical applications in nuclear physics
Medical applications in nuclear physics
The applications of nuclear physics in the medical sector can be divided into two groups, diagnosis and treatment. Most of us have experience with diagnosis whereas a smaller fraction have experience with therapy.
Regarding diagnosis it is mostly X-ray examinations that have been common and used for example in dental care and in cases of fractures. In the last few years one has also started to use more advanced techniques. These are usually based on a radioactive substance (or a substance which can be activated by radiation) being injected into the body. The substances that are used are such that they will search out those parts of the body that one wants to study or participate in special processes. Normally the substances that are used are the same as the ones that take part naturally in processes in the body but where one of the atoms has been exchanged with a radioactive isotope. This is for example the case with PET (Positron Emission Tomography) which is used for studies of the activities in the brain. The principle is that one atom of the stable isotope 12C is replaced by a 11C atom in the substance that is being used. In the decay of the 11C a positron is emitted, and since the positron is the anti-particle of the electron it can easily be annihilated by interacting with an electron. Since there are so many electrons in the vicinity of the positron it will soon be annihilated and two energetic gamma photons will be emitted. The photons go out through the body and can be detected. By detecting both photons it is possible to say from where they came. In addition, by measuring during an extended period of time it is also possible to study the metabolism of the injected substance.
In therapy, nuclear physics has been used in two different ways, on the one hand in irradiation with particle beams and on the other hand in treatment with the injection of radioactive isotopes (or isotopes that can be activated).
Regarding the treatment with injection, the technique is similar to the one used for diagnostics, i.e. one uses substances that have certain atoms replaced by radioactive isotopes. These substances are usually what are called homing substances, i.e. they search out specific organs or types of cells in the body, for instance cancer tumours. In this way healthy tissue can be spared to a larger extent than what is the case with irradiation and surgery. One isotope that is especially suitable for this type of treatment is 10B, which can easily be included in a homing substance and since it is not radioactive it is not dangerous to handle. After the accumulation of the substance in the tumour it can easily be transformed into a radioactive isotope by irradiation with neutrons. When this new isotope decays it will deposit all its energy locally and hopefully the cancer tumour will die.
The treatment can also be done by direct irradiation, traditionally with gamma radiation, which has the disadvantage that also healthy tissue gets high doses. One can minimize the damage in the healthy tissue by irradiating the tumour from several directions, but even so healthy tissue cannot be spared completely. This is simply a consequence of how gamma radiation interacts with matter, it will deposit energy almost uniformly in all the tissue that it passes through.
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treatment at the TSL. |
If one instead uses protons for irradiation one gets quite different possibilities for treatment. This is a consequence of the protons depositing most of their energy just before they stop. Thus one can give a large dose at one depth without the surrounding tissue getting too high a dose. Here a group from Uppsala is actively collaborating with the University hospital and the The Svedberg laboratory. This collaboration has meant that tens of people have been treated among other things for eye melanoma and tumours close to the base of the skull. |