Radiotherapy

Radiotherapy, or colloquially radiation, is the use of ionizing radiation (high-energy rays) for the treatment of malignant diseases. Unlike its use in diagnostics (for example, an X-ray of a broken bone), the doses used are significantly higher, which allows the destruction of tumor cells by damaging their DNA. Cells with DNA damage beyond a certain limit stop dividing or die. Unlike most other types of therapy, radiotherapy does not kill tumor cells immediately, but its effect is delayed. In practice, DNA damage most often occurs within a few days to weeks, and then tumor cells die over a longer period of time that can last for several months after the end of treatment. Unlike most other types of treatment, the purpose of radiotherapy is to be applied locally, i.e. exactly to the area of ​​the body that we want to treat (the area where the tumor is located), and not to the entire body. It can be applied externally (external radiotherapy), which is the most common form of its application, but the radiation source can also be placed inside the body. The choice of radiotherapy type depends on several factors, including the type of tumor, its size, location and proximity to sensitive healthy structures, the patient's general condition, etc.

1. External beam radiotherapy. It is performed using a linear accelerator, a device that produces ionizing radiation. The patient lies still on a table, while part of the device rotates around him to apply therapy from multiple directions. This form of treatment can be used for almost all types of malignant tumors. In addition to the standard approach of external radiotherapy, there is also a special type of such treatment that can apply a significantly larger amount of radiation to a small volume of tissue due to the greater precision of the device, which increases the antitumor effect and also prevents damage to surrounding healthy organs - stereotactic radiotherapy (SBRT), or colloquially radiosurgery.

​2. Internal radiotherapy. This is a treatment where the radiation source is placed inside the body (in the tumor or in the immediate vicinity of the tumor), and it can be in solid (brachytherapy) or liquid form. Brachytherapy is most commonly used for head and neck, breast, cervical, prostate, and eye tumors. Internal radiotherapy in liquid form (radionuclide therapy) is used for thyroid cancer (radioactive iodine I-131), neuroendocrine tumors (so-called PRRT), and neuroblastoma (so-called MIBG).​ Some of these radionuclide therapies specifically target tumor cells, in which case we call it radioligand therapy (RLT).​

Figure 1. Preparing a patient for external beam radiotherapy. During the same radiation treatment, medical staff is in another room to avoid radiation exposure.

Radiotherapy can be used to treat the disease, but also to relieve symptoms (for example, pain in a bone affected by metastasis), and in the latter case it is palliative radiotherapy. It can be used alone, but is most often combined with other types of treatment, either before, during or after them (depending on the type of disease and the goal of treatment). Radiotherapy can be repeated, but care should be taken to limit the healthy tissue in the area being treated. As a rule, after radiation to a certain region, a longer period of time must elapse (usually 5 years) before the same region can be treated again with radiotherapy. However, since it is a local type of treatment, other regions of the body can be treated without difficulty.

Side effects. In addition to tumor cells, radiotherapy can also damage healthy cells in the treated area, and for this reason side effects may occur. Fatigue is a side effect that can occur regardless of the region irradiated, while others depend on the location of the therapy. For example, in radiotherapy for brain tumors, we most often see hair loss, nausea, vomiting and skin changes; in breast cancer, skin changes and swelling; in tumors in the chest (e.g. lung cancer) skin changes, difficulty swallowing and cough; in head and neck tumors, damage to the mucous membrane of the mouth (oral mucositis), loss of taste, difficulty swallowing and hypothyroidism; in tumors in the pelvis and abdomen, diarrhea, nausea, vomiting, sexual dysfunction, loss of fertility and urination disorders. As a rule, the most common side effects are general skin changes. Some of these side effects can significantly make it difficult to eat, and when using therapy, it is very important to take in enough calories and protein so that the body can recover from the effects of ionizing radiation. Therefore, nutritional support in these patients is very important. It is also important to emphasize that side effects in most patients do not occur immediately at the beginning of treatment, but are usually most severe towards the end of therapy. Some patients need several weeks or even months to recover after completing radiotherapy.

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