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What Is Teletherapy In Nuclear Medicine?

Teletherapy, teleradiotherapie or long-distance irradiation, including external percutaneous irradiation, is the most common form of radiotherapy in nuclear medicine. In this type of irradiation, patients are placed and immobilized with special devices on the irradiation table, where they are irradiated with the help of a radiation source located outside their body. Unlike irradiation of brachytherapy (proximity), where the radiation source must be inserted into the body itself.

What is teletherapy in nuclear medicine?

In high-energy X-rays (X-rays) are used in teletherapy. Kilovolt (kV) radiographs radiate tumors located at or just below the patient's skin. For deep tumors (prostate, bladder, cervix, breast, lung), megavolt (MV) x-rays are used, which are rays of higher energies and, therefore, the ability to penetrate more tissue.

The teletherapy process

In the treatment process, the purpose of the treatment (radical or palliative treatment) must be determined. Radiation therapy can also be included as part of the healing process of surgery, chemotherapy, hormonal therapy and immunotherapy. However, cancer treatment can include all of the following. Of course, this depends mainly on the type of cancer, the stage, the local control, the psychophysical condition of the patient. The radiotherapy process can be a radical form of cancer treatment. However, it can be used as part of adjuvant (rescue) therapy, as an adjuvant treatment after initially performed surgery.

High energy X-ray irradiation leads to the destruction of the DNA chain of the tumor tissue cell and, consequently, to cell death. In the irradiation process, high energy X-rays are required, since the goal of radiotherapy is to administer a specific dose of radiation to the tumor tissue at an average target tissue volume at the same time and administer the lowest possible dose to the tissues healthy.

All this contributes to the reduction of side effects, the effects of irradiation and a greater possibility of improving local disease control. To ensure accurate irradiation and disease control, the accuracy and consistency of all segments from the preparation, production of the irradiation plan and the implementation of irradiation is required.

In the modern teletherapy process there is a constant development of newer and therefore more precise radiation techniques and irradiation plans. This is to improve the accuracy of irradiation in terms of increasing the conformity of the dose distribution of isodosis (by adjusting the dose volume to the shape of the tumor), while minimizing the transition from the high dose range to the low dose range .

However, through the development of technologies to verify the pre-irradiation configuration of the patient, it is important to ensure that the patient's daily position is reproducible. It is important to ensure accurate daily irradiation from the first to the last irradiation, with the least possible deviation.

Types of energy irradiation

In the technique of teleterapia we distinguish three types of energy irradiation:

  • Photon Beam Irradiation
  • Irradiation with electron beam
  • Rapid proton irradiation

Photon Beam Irradiation (MV)

They are high energy X-rays, photons. Photons are quanta of energy of a quantified electromagnetic field. It is usually denoted with the symbol γ (Greek letter gamma). In high energy physics, this is usually the designation of high energy photons (gamma rays) generated, and in nuclear decays, in the nuclei of atoms. Photons that are generated in the electron cloud or in the vicinity of the nucleus of an atom (X-rays) are denoted by the letter X.

Photon beam irradiation is the most common irradiation in the teleradiotherapy process. Reference is made to photon irradiation when electrons collide in an inserted irradiation target (a substance with a high Z number) in the path from the accelerator tube.

In the irradiation target, brake radiation is generated, which results in high energy photons that subsequently hit the leveling filter, which compensates for the dose profile. An additional beam restriction is required, which deals with the openings.

Irradiation with electron beam (MeV)

In electron beam irradiation, the accelerated electrons collide in a thin metal dispersion film, which has the task of guaranteeing the homogeneity of the irradiation field over the entire dose profile of flat doses. Limit the irradiation field with special tubers to reduce the irradiation field to the desired size. The electron beam is precisely limited by individual protections consisting of a wooden alloy.

The most common electron irradiation energies are: 6, 9, 12, 15 and 18 MeV and are mainly used for irradiation of shallow tumors that have a bed just under the skin, or for additional irradiation to the tumor site , which has previously been surgically removed, and irradiated by photon beams. Electronic irradiation is also used as an intraoperative electronic radiotherapy (IOERT) process, which is the irradiation process during surgery at the site of the tumor where the tumor was removed.

Electronic irradiation is a very useful irradiation, since the profound drop in the dose in electronic irradiation is very rapid, which means that, in terms of energy, electronic radiation reaches its maximum dose quickly and has a strong dose drop in healthy tissue.

Rapid proton irradiation

Proton therapy is a type of particle irradiation that uses protons to destroy diseased tissue, most commonly cancer cells. Most of the energy is released at a specific depth, with energy absorbed before and at that negligibly low depth. Therefore, this type of irradiation has fewer side effects compared to radiation ɣ.

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Published: February 4, 2020
Last review: January 4, 2020