Radiation therapy is a treatment that uses ionizing radiation (a type of energy) to destroy or disable the duplication of tumor cells, to control pain caused by some types of cancer and also to reduce the size of tumors that are compressing an organ. In it, the DNA of cancer cells is hit by radiation, which prevents their reproduction – as a result, they stop developing.
Some healthy cells may also end up being affected during radiation therapy, but to a lesser extent. Although they have a greater capacity for recovery, in some treatments the sessions are divided to give the body time to strengthen itself again.
In addition, radiation doses and application time are calculated according to the type and size of the tumor, which also helps to preserve healthy cells.
According to the WHO (World Health Organization), approximately 60% of patients diagnosed with cancer will undergo radiotherapy at some stage of their treatment. It is worth noting that this procedure is painless.
Benefits of radiotherapy
The results of radiotherapy are usually quite positive: the tumor can disappear and the disease can be controlled or even cured.
When a cure is not possible, radiotherapy can contribute to a better quality of life, as its applications reduce the size of the tumor, which relieves pressure, reduces bleeding, pain and other symptoms of certain types of cancer, providing relief to patients.
The situations in which radiation therapy is most commonly used are:
- Exclusive – when used as the only cancer treatment;
- Curative or radical – when radiotherapy is considered the main tool in the fight against cancer;
- Neoadjuvant – when it is performed before surgery to reduce the size of the tumor (may or may not be combined with chemotherapy);
- Adjuvant – when performed after surgery (with or without a combination of chemotherapy), to reduce the risk of recurrence by stopping the growth of any remaining cancer cells;
- In combination with other treatments – such as chemotherapy (radiochemotherapy), without the involvement of surgery; and
- Palliative use – in patients with advanced cancer, as a way of relieving symptoms.
Types of radiotherapy
There are several types of radiotherapy. Understand them below.
External radiotherapy consists of the emission of a beam of external and long-distance radiation, usually X-rays or high-energy electrons, produced by a device called a linear accelerator. The target is the tumor. Most people undergoing radiation therapy receive this type of treatment.
The patient remains lying on a treatment table and radiation is emitted by the linear accelerator, positioned at a safe distance from the person. Applications are usually daily, but the number of sessions and intervals are defined on a case-by-case basis.
To schedule the treatment, the tumor and adjacent healthy organs are identified using computed tomography. With this information, a dedicated software makes the precise calculation of the radiation distribution in the patient. Location references are marked on the skin to aid in positioning the linear accelerator.
A plastic mask-like mold can be made so that the radiation reaches only the area to be treated, sparing the healthy tissue around it, when the targets are in the head and neck region. In this case, the marking of the area to be treated is done directly on the mold, and not on the skin. In other areas of the body, locating accessories such as vacuum mattresses and attachment brackets may be needed.
Teletherapy is another modality of radiotherapy and has several subtypes, which are:
- Conventional radiotherapy (2DRT) – of lesser complexity, it uses images from simple radiographs or even topographic anatomy to identify the target. It usually presupposes large radiation fields and greater involvement of healthy tissues;
- Conformal or three-dimensional radiotherapy (3DRT) – uses computed tomography for treatment planning, which consists of static incidences of radiation beams that, combined, involve the target area;
- Beam intensity modulated radiotherapy (IMRT) – type of treatment in which there is the possibility of modulating the treatment dose to heterogeneous targets, allowing the reduction of incidence in healthy tissues close to tumors and dose escalation;
- Volumetric Arc Radiotherapy (VMAT) – IMRT technique in which radiation is delivered in a dynamic arc, with the linear accelerator gantry moving during the session. It usually has a faster dose delivery in the treatment;
- Radiosurgery – technique for high-precision treatment of cranial lesions, such as metastases, benign tumors and arteriovenous malformations, without the need to open the skull. It usually lasts from one to five sessions;
- Extracranial stereotactic radiotherapy – technique that also requires high precision, performed in few fractions, for radical or palliative ablative (tumor destruction) treatment of primary or metastatic tumors. Used in lung, liver, lymph node tumors and in metastases in general;
- Image-guided radiotherapy (IGRT) – a technique that incorporates the image at the time of dose delivery, ensuring better accuracy and reducing the need for more generous safety margins. Digital radiographs, ultrasound or cone beam tomography can be used, incorporated into the linear accelerator; and
- TBI (Total Body Irradiation) – technique used in bone marrow transplant preparation to reduce the risk of rejection.
Another type of radiotherapy is internal radiotherapy or brachytherapy, which uses internal radiation sources placed very close or in direct contact with the target – unlike external radiation, in which the source emitting radiation is far from the target. It also requires a simulation to choose the best approach.
In it, the radioactive material used is in the form of seeds, wires or plates and is administered through catheters, applicators or needles. It is usually indicated for the treatment of prostate cancer, retinoblastoma, gynecological tumors, head and neck cancer, sarcomas, choroidal melanoma (inside the eyes), skin and sarcomas, among others.
It is usually said that in brachytherapy the radiation goes from the inside to the outside and in teletherapy, from the outside to the inside.
Finally, intraoperative radiotherapy is the technique in which the administration of radiotherapy takes place during the surgical procedure. Electron teletherapy, brachytherapy or even orthovoltage equipment can be used.
Difference between chemotherapy
Both treatments aim to reduce the cancer cell’s reproductive capacity, but they are quite different. Chemotherapy uses drugs and reaches every cell in the body as they are carried in the blood. Radiotherapy, on the other hand, uses ionizing radiation and has an effect on the areas where it is applied, being more indicated, in most cases, for local or regional disease control.
Possible adverse effects and complications
Radiation therapy can have adverse effects, which depend on the part of the body exposed to it and the amount of radiation used. Most of them are temporary, can be controlled, and usually disappear after treatment ends.
The following are some of the most commonly observed adverse effects in cancer patients undergoing radiotherapy:
- Any area – hair loss at the treatment site (sometimes it can be permanent), skin irritation at the application site and fatigue;
- Head and neck – dry mouth, thickening of saliva, difficulty swallowing, sore throat, change in food taste, nausea, mouth sores, tooth decay;
- Chest – difficulty swallowing, coughing, shortness of breath;
- Stomach and abdomen – nausea, vomiting, diarrhea;
- Pelvis – diarrhea, bladder irritation, frequent urination, sexual dysfunction, rectal irritation; and
- Breast – fatigue, skin changes, swelling and tenderness.
