Teletherapy

Teletherapy is percutaneous radiation therapy (through the skin) in which the radiation source is by definition outside the body and the focus-to-skin distance must be at least 10 cm. Thus, radiation is delivered from a distance, and the tumor and the radiation source are not in direct contact. Teletherapy includes:

  • X-ray therapy (soft and hard radiation therapy).
  • High energy therapy/telegam therapy (with 60 cobalt).
  • High energy therapy with accelerators (linear or circular accelerators).

Percutaneous radiotherapy is the most common form of radiation treatment.

Indications (areas of application)

An indication for teletherapy is all radiation-sensitive tumors that are not located on the body surface or in hollow organs and are therefore unsuitable for short-distance irradiation (brachytherapy). The type of radiation or irradiation technique used depends on the individual tumor and patient.

Before the examination

Each radiation therapy must be planned individually and carefully. For this purpose, the patient and tumor geometry must first be determined using CT and/or MRI data (computed tomography (CT) or magnetic resonance imaging, MRI). This is followed by the three-dimensional adaptation of the irradiation dose distribution to the actual target volume. The task of radiation planning is to determine suitable types of radiation and radiation techniques in order to achieve maximum concentration of the radiation dose at the tumor while sparing the surrounding normal tissue as much as possible. A 3D data set based on imaging techniques (usually CT) is created on the computer, the irradiation geometry is determined, and the dose distribution is optimized. The dose fall-off outside the target volume should be as steep as possible to spare nearby organs. To avoid iatrogenic (physician-induced) radiation damage, doses to the respective organs at risk should be below the specific tolerance dose (radiation dose that causes radiation damage in up to 5% (TD 5/5) or 25-50% (TD 50/5) of organs (TD stands for lethal dose) within 5 years). An important component of radiation planning is the therapy simulator. This is an X-ray facility specifically designed for radiation therapy planning, with diagnostic X-ray tubes for fluoroscopy and X-rays, as well as image intensifiers and a patient couch. With the help of the therapy simulator, geometric setting and movement options of the radiation equipment can be mimicked so that the localization, determination and documentation of the radiation fields is successful.

The process

Various irradiation techniques exist that determine the dose distribution in the tissue and must always be individually selected and planned depending on the patient or tumor.

  • Single standing-field irradiations: In this technique, individual irradiation fields are placed next to each other and their position is not changed during irradiation. A suitable application is surface and half-depth therapy to a maximum depth of 3 cm. Depending on the type of radiation, the maximum dose is either in the skin (soft rays of X-ray therapy), at a depth of 5 mm (telegamma therapy) or at a depth of more than 1 cm (electron beams of a linear accelerator). The juxtaposition of the individual radiation fields must be carefully planned in advance to prevent over- and under-dosing in the overlapping zones of the radiation beams.
  • Multiple-field irradiations:
    • Opposing field irradiation: the irradiation fields are placed exactly opposing (opposite), so that the two central beams run into each other.
    • Cross-fire irradiation: two or more individual standing fields are used, which are directed towards the isocenter at an angle to each other. In this way, a high dose is achieved in the target volume, while the surrounding healthy tissue is largely spared.
  • Motion irradiations: The radiation source moves in an arc around the patient during irradiation. Although only one radiation source is used, the movement allows radiation to be delivered from different angles, making motion irradiation a form of multi-field crossfire technique.
  • Conforming radiotherapy: this type of radiotherapy refers to the tissue-sparing adaptation of the irradiation field in order to irradiate a complexly shaped target volume very precisely and to spare the neighboring structures to a maximum. The planning and execution of the irradiation are very complex, must always be individually adapted and usually involve a combination of different irradiation techniques (multi-field techniques, multi-segmental motion irradiation, etc.). The indication is mainly for small target volumes in the vicinity of radiation-sensitive normal structures such as in the brain, brain stem, spinal cord, or also for peripheral lung tumors and liver metastases. Highly complex and currently developing types of conformal radiotherapy include stereotactic radiotherapy, radiosurgery, dynamic radiotherapy, or intensity-modulated radiotherapy.
    • Stereotactic ablative radiotherapy (SBRT; “stereotactic body radiotherapy”) or body stereotactic radiotherapy: the procedure has a steeper dose gradient between tumor and surrounding normal tissue; increasingly used in patients with oligometastases (1-5 metastases) [randomized phase III trial lacking to date].
  • Intraoperative irradiation (IORT): IORT is performed immediately after surgical removal of a tumor in the operating room with the site still open. Electron radiation from a linear accelerator is usually used; alternatively, the flab technique with 192-iridium emitters is available. The main advantage of this irradiation is the ability to bring the radiation source through the surgical circumstances in direct contact with the tumor remnant and spare the surrounding tissue.
  • Large-field irradiations: This is an extended irradiation of large target volumes. Indicated is a large-field irradiation, for example, if the primary tumor including its lymphatic drainage area should be irradiated, in addition, in lymphoreticular systemic diseases (Hodgkin’s disease, non-Hodgkin’s lymphoma), for the destruction of bone marrow stem cells before a bone marrow transplant or for pain treatment of a strongly extended metastasis.

Notice:

  • Fractionation can increase the maximum tolerated total dose of normal tissue many times.
  • The shorter the total treatment time, the greater the chance of cure.

Possible complications

Not only tumor cells, but also healthy body cells are damaged by radiotherapy. Therefore, it is always necessary to pay careful attention to radiogenic (radiation-related) side effects and to prevent them, if necessary, detect them in time and treat them. This requires a good knowledge of radiation biology, radiation technique, dose and dose distribution as well as permanent clinical observation of the patient. The possible complications of radiotherapy are essentially dependent on the localization and size of the target volume. Prophylactic measures must be taken especially if there is a high probability of side effects occurring. Common complications of radiation therapy:

  • Intestinal disorders: Enteritides (intestinal inflammation with nausea, vomiting, etc.), strictures, stenoses, perforations, fistulas.
  • Limitations of the hematopoietic system (blood-forming system), especially leukopenias (decreased number of white blood cells (leukocytes) in the blood compared to the norm) and thrombocytopenias (decreased number of platelets (thrombocytes) in the blood compared to the norm)
  • Lymphedema
  • Mucositides (mucosal damage) of the respiratory and digestive tracts.
  • Pericarditis (inflammation of the pericardium) (6 months to 2 years after therapy).
  • Radiogenic dermatitis (radiation dermatitis; radiation-induced skin inflammation).
  • Radiogenic pneumonitis (collective term for any form of pneumonia (pneumonia), which does not affect the alveoli (alveoli), but the interstitium or the intercellular space) or fibrosis.
  • Radiogenic nephritis (radiation nephropathy; radiation-induced inflammation of the kidneys) or fibrosis.
  • Secondary tumors (secondary tumors).
  • Radiation syndromes in the central nervous system (a few months to several years after therapy).
  • Teleangiectasias (visible dilatations of superficially located small blood vessels).
  • Tooth and gum damage
  • Cystitis (inflammation of the urinary bladder), dysuria (difficult emptying of the bladder), pollakiuria (frequent urination).