Generality
Radiation therapy can be administered as external radiotherapy, in which the source of the radiation is external to the organism, or how internal radiotherapy, in which the radioactive source is inserted inside the organism.
The treatment plan is designed in such a way that the highest possible dose of radiation selectively affects the cancer cells, sparing the healthy ones. Therefore, the aim is to obtain the maximum result by trying to minimize the risk of the appearance of side effects.
External radiotherapy
In this type of radiotherapy, the source of the radiation (X-rays, γ rays or particle beams) is constituted by a device external to the patient's body. The device does not come into contact with the patient's body and does not cause pain. Usually, hospitalization is not required, but is done on an outpatient basis.
Before proceeding with the therapy it is necessary to define the exact position of the tumor through the use of diagnostic techniques and three-dimensional reconstructions.
The radiotherapy device is equipped with an internal system of blades that allow for customized shielding of the outgoing radiation, so that it affects only the affected area.
However, there are many types of devices with different characteristics and which use different techniques to irradiate the tumor. Among the main techniques are:
- Conventional external radiotherapy: use appliances (linear accelerators) that generate high-energy X-rays. The radiation is aimed at the tumor mass from different angles, so as to intersect at the center of the area to be treated. It is a well-established, rapid and rapid type of radiotherapy. However, some treatments that involve the administration of a high dose of radiation they can be limited due to the high toxicity they have towards healthy tissues.
- Three-dimensional conformational radiotherapy (3D-conformal radiotherapy or 3D-CRT): this technique uses radiation that is shaped according to the shape and volume of the tumor. By doing so, a greater absorption of radiation by the tumor and a saving of healthy cells that are nearby are guaranteed.
- Intensity modulated radiotherapy (intensity-modulated radiotherapy or IMRT): this technique can be defined, in a certain sense, as the evolution of the three-dimensional conformational radiotherapy described above. This type of radiotherapy allows to irradiate with the utmost precision tumors with very complex shapes and volumes and / or that are close to the of critical areas of the organism (spinal cord, vital organs, important blood vessels).
This technique uses computerized linear accelerators able to distribute extremely precise doses of radiation on the tumor mass or on specific areas of the tumor. The intensity of the radiation will be greater in the heart of the tumor mass, while it will be reduced in areas where the tumor is located near healthy tissues. - Image-guided radiation therapy (image-guided radiotherapy or IGRT): this modern technique uses radiological images to monitor and identify the real position of the tumor mass just before the "emission of radiation. In this way there is a" more precise irradiation of tumors involving organs that are susceptible to displacement; such as, for example, the prostate gland.
- Body stereotaxic radiotherapy (stereotactic body radiotherapy or SBRT): it is a particular type of radiotherapy that allows a highly precise irradiation of the tumor mass, adapting well to small volumes and allowing a considerable saving of healthy tissues. Initially it was applied only to the brain, but now it is also applicable in other locations of the "organism having certain characteristics.
- 4D radiotherapy (Adaptive radiotherapy): is an innovative radiotherapy system that takes into account the movement of organs due to the patient's breathing and intestinal peristalsis. Usually - if breathing or peristalsis is not considered - to be sure that the entire tumor is affected, it is necessary to irradiate a larger area, including healthy cells. With this technique, however, the tumor mass is affected in a very precise way, also allowing the treatment of inoperable tumors. The devices used are able to record the patient's respiratory movement and to administer radiotherapy at a precise moment of the respiratory act with high accuracy. In addition, these devices can also perform intensity modulated radiotherapy And body stereotaxic radiotherapy.
- Hadron therapy or particle therapy: it is a type of radiotherapy that uses beams of ionizing particles (protons, neutrons or positive ions). The characteristic of these particles is that - unlike ionizing radiation - when they penetrate the tissues they release most of their energy at the end of their path. Therefore, the greater the thickness that the particle has to pass through, the greater the energy it releases. The advantage of this technique lies in the fact that in the healthy tissue surrounding the tumor, there is less energy deposited, thus saving it. from unnecessary damage.
This technique is mainly used in lung, liver, pancreas, prostate and gynecological cancers.
Generally, after the external radiotherapy session, no traces of radiation remain in the body. The patient can then approach anyone without worrying about harming other people, including children and pregnant women.
With the advancement of technologies, the side effects of this therapy have been reduced and the patient can continue his usual activities. However, the response to radiotherapy varies from individual to individual.
Internal radiotherapy
This type of radiotherapy involves the introduction of radioactive substances into the body. In this case, hospitalization is often foreseen for the administration for a short period.
The radiation sources used can be liquids or radioactive metals.
THE radioactive liquids they can be administered orally or intravenously. Radiation therapy using radioactive liquids is called systemic radiotherapy or metabolic.
The radioactive element of the liquid is an isotope which is usually found bound to a molecule having a high affinity for cancer cells and which preferably binds to them, leaving the healthy ones unaltered.
THE radioactive metals are found in the form of tiny cylinders, otherwise defined "seeds". They are employed for the so-called radioactive systems, that is, the metal seeds are placed near the tumor or directly inside it. This particular treatment is called brachytherapy.
We can distinguish three types of brachytherapy:
- Endocavitary brachytherapy: the radioactive source is placed - with the use of special probes - in natural cavities of the organism that are located near the tumor (for example in the uterus or bladder).
- Interstitial brachytherapy: in this case the radioactive source is implanted inside the tumor with a minimally invasive surgery.
- Episcleral brachytherapy: this type of brachytherapy is used for the treatment of uveal melanoma (an intraocular tumor); the source of radiation, through surgery, is inserted at the base of the tumor mass.
The radioactive sources are left in the organism for periods ranging from a few minutes to a few days. After this time the sources are removed.
The patient can emit radiation only as long as the source is internal to the body. Contact with other people is therefore avoided by being hospitalized in a screened room.
For the treatment of some types of cancer, such as prostate cancer, the source must remain inside the body for very long periods. In this case, however, the release of radiation occurs in a high manner only in correspondence with the tumor and it propagates little in the surrounding tissues and not at all outside the body. The patient, therefore, does not emit radiation and does not constitute a danger to the In any case, it is common practice to advise against contact with children and pregnant women immediately after the administration of radiotherapy, for a period that varies according to the type of treatment performed.
Radioactive isotopes in radiotherapy
Radioactive isotopes can be administered orally or by intravenous infusion. The main isotopes used are shown below.
- Iodine 131 (131I): iodine 131 is used both in diagnostics (thyroid scintigraphy) and in radiotherapy. This radioisotope is mainly used in the treatment of "hyperthyroidism (thyrotoxicosis) and in the treatment of some types of thyroid cancer. Patients undergoing this therapy are usually advised to avoid sexual intercourse for a time that varies depending on the dose administered. In the case of women - as a precaution - it is advisable to avoid pregnancies for the six months following the treatment, this because it could cause harm to the fetus.
However, the guidelines on post-therapeutic isolation vary from hospital to hospital and it is always advisable to ask your doctor for detailed information. - Cobalt 60 (60Co): radiotherapy carried out with cobalt 60 is called telecobalt therapy. It is a type of external radiotherapy that uses the γ rays emitted by this radioisotope. The radiations produced have a high penetration power and are mainly used in the treatment of tumors in deep areas of the organism (for example, esophagus, lungs, bladder and mediastinum).
- Yttrium 90 (90Y): this radioisotope is administered in the form of microspheres that are injected into the hepatic artery in certain types of liver tumors or in the case of liver metastases.
Yttrium 90 can also be conjugated with other anticancer drugs. An example is that of the anticancer drug Zevalin ® (ibritumomab tiuxetan). This drug consists of a monoclonal antibody conjugated to yttrium 90 and is used in the treatment of non-lymphomas. Hodgkin. He was one of the first agents to join what is now called "radioimmunotherapy'. - Other isotopes used in radiotherapy are lo iodine 125 (125I), the ruthenium 106 (106Ru), the lutetus 177 (177Lu), lo strontium 89 (89Sr), the samarium 153 (153Sm) and the rhenium 186 (186Re).
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