High-Energy Therapy (High-Voltage Therapy) with Accelerators

High-energy therapy is a type of radiation therapy in which electrons are accelerated to produce ultra-hard X-rays using accelerators. In principle, all charged and uncharged particles can be accelerated (e.g., protons, ions). In clinical routine, however, only electrons are used nowadays. In terms of the technical designs of accelerators, a distinction is made in principle between linear accelerators (straight-line acceleration path) and circular accelerators (circular particle path).

Indications (areas of application)

High-energy therapy with accelerators is used for various tumor types. Examples of applications for electron irradiation are:

The procedure

The basic physical process in accelerators is the same as in X-ray tubes. Electrons become highly energetic when accelerated, so they emit X-ray bremsstrahlung and heat when decelerated in a target (irradiation target). The electrons are injected into the accelerating path by an injector. When a target is inserted into the beam, the desired ultra-hard X-ray bremsstrahlung is produced. The required field size is achieved by a collimator system that confines the beam. Circular accelerator: The electrons are accelerated along a spiral particle path through an increasing magnetic field. The circular path must be traversed several times until the desired acceleration energy is reached. In clinical practice, the betatron, cyclotron, or synchrotron are used as different design principles. Most electron accelerators in the 1960s to 1980s operated on the betatron principle, in which free electrons were accelerated in a vacuum tube in a magnetic field to approximately the speed of light. Since then, circular accelerators have largely been replaced by more powerful linear accelerators. Linear accelerator: The electrons pass through a straight acceleration path. Acceleration is achieved by a high-frequency electric field established between a series of cylindrical electrodes in an accelerating tube. A standing field can be established (standing wave principle) or the field travels with the electrons (traveling wave principle). After exiting the accelerating tube and being focused (deflected by 270°), the high-energy electrons hit the target (target) and generate the ultra-hard X-rays. Accelerators in use today are automatic, computer-controlled and computer-monitored systems consisting of five components: Modulator, power supply, accelerator unit, emitter head and control panel.

Potential complications

Not only tumor cells but also healthy body cells are damaged by radiotherapy. Therefore, careful attention must always be paid to radiogenic side effects and these must be prevented, detected in time if necessary, and treated. 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:

  • Radiogenic dermatitis (skin inflammation).
  • Mucositides (mucosal damage) of the respiratory and digestive tracts.
  • Tooth and gum damage
  • Intestinal diseases: Enteritides (intestinal inflammation with nausea, vomiting, etc.), strictures, stenoses, perforations, fistulas.
  • Cystitis (urinary bladder infections), dysuria (difficult bladder emptying), pollakiuria (frequent urination).
  • Lymphedema
  • Radiogenic pneumonitis (inflammatory changes in the lungs) or fibrosis.
  • Radiogenic nephritis (inflammation of the kidneys) or fibrosis.
  • Limitations of the hematopoietic system (blood-forming system), especially leukopenias (decreased number of white blood cells (leukocytes) in the blood compared with the norm) and thrombocytopenias (decreased number of platelets (thrombocytes) in the blood compared with the norm)
  • Secondary tumors (second tumors).