Generality
Radiation therapy can be administered as external radiotherapy, in which the source of the radiation is external to the organism, or as 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 cancer cells, sparing healthy ones. Therefore, the aim is to obtain the maximum result by trying to minimize the risk of side effects.
External radiotherapy
In this type of radiation therapy, the source of the radiation (X-rays, γ-rays or particle beams) consists of an apparatus external to the patient's organism. The device does not come into contact with the patient's body and does not cause pain. Usually, hospitalization is not necessary, but is performed 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 device for radiotherapy is equipped with an internal system of lamellae that allow to have personalized shields of the outgoing radiation, so that it affects only the affected area.
In any case, there are many types of devices with different characteristics and that use different techniques to irradiate the tumor. The main techniques include:
- External conventional radiotherapy : it uses devices ( linear accelerators ) that generate high-energy X-rays. Radiation is directed at the tumor mass from different angles, so that it intersects the center of the area to be treated. It is a type of consolidated radiotherapy, fast and fast. However, some treatments that involve the administration of a high dose of radiation can be limited due to the high toxicity they have towards healthy tissues.
- Three - dimensional conformal radiotherapy ( 3D-conformal radiotherapy or 3D-CRT ): this technique uses radiations that are shaped according to the shape and volume of the tumor. By doing so, you are guaranteed a greater uptake of radiation by the tumor and a saving of healthy cells that are nearby.
- Modulated intensity radiotherapy ( intensity-modulated radiotherapy or IMRT ): this technique can be defined, in a certain sense, as the evolution of the three-dimensional conformal radiotherapy described above. This type of radiation therapy allows tumors to be irradiated with very complex shapes and / or volumes that are in proximity to critical areas of the body (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 the areas where the tumor is located near healthy tissues.
- Image -guided radiotherapy ( image-guided radiotherapy or IGRT ): this modern technique uses radiological images to monitor and identify the actual position of the tumor mass just before the radiation emission. 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.
- Stereotactic body 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 encephalon, but now it is also applicable in other locations of the organism with certain characteristics.
- 4D Radiotherapy ( Adaptive radiotherapy ): an innovative radiotherapy system that takes into consideration the movement of the organs due to the patient's breathing and intestinal peristalsis. Usually - if breath or peristalsis is not taken into consideration - a larger area, including healthy cells, must be irradiated to make sure it affects the entire tumor. With this technique, on the other hand, the tumor mass is hit very precisely, also allowing the treatment of inoperable tumors. The appliances 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. Furthermore, these devices can also perform modulated intensity radiotherapy and stereotactic body radiotherapy .
- Hadronic 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 radiations - when they penetrate the tissues they release most of their energy at the end of their path. Therefore, the greater the thickness the particle must pass, 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 used mainly in lung, liver, pancreas, prostate and gynecological tumors.
Generally, after the external radiotherapy session, no traces of radiation remain in the body. The patient can then approach anyone without worrying about causing harm to other people, including children and pregnant women.
As technology advances, the side effects of this therapy have been reduced and the patient can continue his usual activities. However, the response to radiation therapy 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 provided for a short period for administration.
The radiation sources used may be liquids or radioactive metals .
Radioactive liquids can be administered orally or intravenously. Radiotherapy that uses radioactive liquids is called systemic or metabolic radiotherapy .
The radioactive element of the liquid is an isotope which is usually found bound to a molecule having a high affinity for tumor cells and which preferably binds to them, leaving healthy ones unaltered.
Radioactive metals are found in the form of tiny cylinders, otherwise called " seeds ". They are used for so-called radioactive implants, ie 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 arranged - with the use of special probes - in natural cavities of the organism that are near the tumor (for example in the uterus or in the 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.
Radioactive sources are left in the body 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 through hospitalization within a screen room.
For the treatment of some types of tumors, such as prostate cancer, it is necessary for the source to remain inside the body for very long periods. In this case, however, the release of radiation occurs only in a high way in correspondence of the tumor and propagates little in the surrounding tissues and not at all outside the body. Therefore, the patient does not emit radiation and is not a danger to other people. In any case, it is common practice to advise against contact with children and pregnant women immediately after 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 the diagnostic field ( 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 according to the dose administered. In the case of women - in precautionary form - it is advisable to avoid pregnancies for the six months following the treatment, this because it could cause damage to the fetus.
However, the guidelines on post-therapeutic isolation vary from hospital to hospital and it is always advisable to ask the doctor for detailed information.
- Cobalt 60 (60Co): radiotherapy performed with cobalt 60 is called telecobaltotherapy . It is a type of external radiotherapy that uses the γ rays emitted by this radioisotope. The radiation produced has a high penetration power and is mainly used in the treatment of tumors in deep locations of the body (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 some 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-Hodgkin's lymphomas. He was one of the first agents to become part of what is now called " radioimmunotherapy ".
- Other isotopes used in radiotherapy are iodine 125 (125I), ruthenium 106 (106Ru), Lutetium 177 (177Lu), strontium 89 (89Sr), samarium 153 (153Sm) and rhenium 186 (186Re).
