Radiation Therapy

Radiation Therapy

Radiotherapy (RT), also called radiation therapy, was first used to treat cancer about a century ago. Since then, great technological progress has been made to increase the effectiveness of this method and minimize side effects.

Increasingly, radiotherapy is used in conjunction with surgery and systemic treatments to improve tumor control, quality of life and reduce side effects. The best treatment results are achieved by evaluating each patient by a multi-disciplinary cancer treatment team. This team includes radiation oncologist, medical oncologist, surgeon and other specialists.

Radiotherapy has many different forms of administration and purposes:

  • as a single treatment,
  • with systemic agents,
  • before or after surgery, to minimize the chance of remaining microscopic tumors,
  • for support when the disease is at an advanced stage

The duration of treatment can vary from a single session to 8 weeks of daily administration. The technique, dose, expected benefits, and side effects for each different patient may vary depending on the diagnosis and treatment area.

Protection of healthy organs other than tumors has become one of the important issues of oncology (organ-preserving treatments). In certain types of cancer, such as breast and laryngeal cancer, the long-term results of patients in whom only the tumor is removed with some normal tissue around it and adjuvant radiotherapy is applied, instead of radical surgery in which the entire organ is removed, are equivalent to each other. In fact, as expected, organ preservation procedures offer fewer side effects.

How does Radiotherapy Work?

In this treatment method, in which the clinician specifically targets a certain area, radiation energy is used to kill cancerous cells.

Radiotherapy damages the DNA of cancer cells by ionizing atoms – breaks in the DNA double helix.

In the treated area, both cancerous and normal cells are exposed to the ionizing effect of radiation. However, normal cells are faster at detecting and repairing DNA damage caused by radiation. Cancer cells, on the other hand, are proliferation-oriented, faster in growth and proliferation, and therefore have disadvantages compared to normal cells in repairing DNA damage. However, there are maximum total dose limits that normal tissues can withstand radiation. Here the balance must be well adjusted. Dividing the total dose of radiation into small daily doses (fraction) allows normal tissues to repair themselves.

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  1. External radiotherapy
  2. Brachytherapy (internal radiotherapy)
  3. Intraoperative (during surgery) radiotherapy

High-resolution imaging is needed for stereotactic methods. It is especially preferred in well-defined small tumors (for example, when lung cancer has metastasized to a single spine).

Since a high dose of radiation is given to a certain point, the immobilization of the patient is more important in this method.

Brachytherapy (Internal Radiotherapy)

In brachytherapy, the radiation source is placed next to or inside the treatment area. It is especially preferred in prostate cancers and gynecological malignancies such as cervical (cervix) cancer.

For example, brachytherapy appears as a treatment option in regional (early stage) prostate cancer. The system with a low dose rate (LDR) is applied to the patient at once. Radioactive sources are permanently placed in the prostate gland under ultrasound guidance. Slow radiation emission from these sources occurs over months.

Intraoperative (during surgery) Radiotherapy (IORT)

It is the application of radiation during surgery. External radiotherapy has advantages in terms of some limitations, such as damage to normal tissues. It is applied as a single session during the surgery and the application dose is limited to structures that cannot be visualized at that moment (nerves, fixed organs).

If there is a high probability of regional recurrence of the cancer (if the tumor in the surgical margins is shown by the pathology sample (frozen) taken during the operation or if the tumor has not been completely removed), the decision to apply IORT can be made during the surgery.

The application area is mostly inguinal and intra-abdominal cancers. However, adequate tumor control is often not achieved with a single dose of IORT, and external radiotherapy must complement this treatment.

Treatment Planning

Treatment plan;

  • careful fixation of the patient,
  • determination of the area to be irradiated by radiological methods such as computed tomography (CT) or magnetic resonance imaging (MRI = MRI), and
  • calculation of dose and frequency of administration.

Different tumors have different radiotherapy sensitivities. For example, while lymphoma and seminoma, a type of testicular cancer, are extremely sensitive to radiotherapy (radiosensitive) and can be completely treated with radiotherapy; skin cancer, malignant melanoma and soft tissue sarcomas are radioresistant and require higher doses of radiation to act on these tumors.

Possible Side Effects of Radiotherapy

Side effects experienced by patients during or after radiotherapy are largely dependent on the anatomical region being treated. It also correlates with factors such as the total dose, the dose in each fraction, the sensitivity of tissues to radiotherapy, and other cancer treatments (chemotherapy and surgery).

External Radiotherapy

It is the most commonly used radiotherapy method. A radiation source (external beam) located outside the patient is used.

Accelerating charged particles such as electrons or protons, or Cobalt-60, is used to produce ionizing radiation.

Linear accelerator: in this device, electrons are accelerated to reach higher energy and become X-rays (also known as photons). It can produce photon or electron beams of various energies, and their output is managed by advanced computer controls.

Electrons versus photons: photons can reach deeper tissues and are preferred in cancers of internal organs. Electrons are often preferred in superficial tumors such as breast and skin cancers, thus preventing damage to internal organs. Often, photons and electrons are combined to achieve the best tumor and normal tissue dose distribution.

There are different techniques for external radiotherapy:

Conformal Rherapy

This term is used to describe a strategy of delivering high doses of radiation to the tumor area and as little as possible to normal tissues. By using advanced imaging methods such as CT and MRI, with 3-dimensional conformal RT (3D-CRT), radiation oncologists can calculate and adjust the radiation dose of the tumor and adjacent normal tissues separately. Thus, side effects are minimized. It also allows an irradiated area to be re-irradiated later if needed.

3D-CRT applications are examined under two headings:

  • Intensity modulated RT (intensity modulated RT=IMRT): IMRT, which is an advanced form of 3D conformal radiotherapy, allows the radiation beam from a single source to be applied to different parts of the target at different intensities.
  • Imaging guided RT (image guided RT=IGRT)

Proton Therapy

Irradiation with proton therapy, which is a special form of external radiotherapy, allows less damage to normal tissues and more sensitive radiotherapy to the tumor area due to the unique physical properties of heavy particles. Protons can penetrate tissues at different depths; When it reaches the target tissue, it releases its energies sharply, this is called the Bragg peak.

Although it is investigated whether protons have an advantage over photons in many cancer types, some childhood cancers, uveal melanoma, etc. No superiority was demonstrated except for the disease group. The results of proton therapy, which has been tried intensively especially in prostate cancer, were found to be equivalent to 3-dimensional conformal techniques.

Stereotactic Radiotherapy Techniques (SBRT and radiosurgical SRS)

It is the application of the total calculated radiation dose in one or several times (fractions).

Stereotactic radiosurgery (SRS) in brain tumors; stereotactic body radiation therapy (SBRT) is used to irradiate non-brain organs such as the lungs, spine or liver.

As a general rule, tissues swell during radiotherapy. As a result, edema is seen in the target tissue. Most acute (sudden onset) side effects are anticipated and limited to the site of radiotherapy. Radiation to the abdominal region causes side effects such as nausea and vomiting. Radiotherapy to the head and neck area may cause mouth and throat sores, while radiotherapy to the thorax (chest) may result in inflammation of the esophagus. These conditions cause dysphagia (difficulty in swallowing), decrease in oral food intake and dehydration (water loss), respectively. Radiotherapy to the pelvic (lower abdomen) region causes urinary and intestinal changes. Edema and tissue irritation (discomfort) decrease after treatment, and acute side effects disappear to a large extent.

Over time, the technology used in radiation oncology also improved and became more sensitive. After the X-rays used in the early periods of history, high-energy photons, electrons, protons and neutrons began to be applied. In addition, thanks to the technological developments in the field of computers and electronics, a level close to perfection has been reached in treatment planning and application.