Electron beam therapy is performed using a medical linear accelerator. The same device can also be used to produce high energy photon beams. When electrons are required, the x-ray target is retracted out of the beam and the electron beam is collimated with a piece of apparatus known as an applicator or an additional collimating insert, constructed from a low melting point alloy.
Electron beams have a finite range, after which dose falls off rapidly. Therefore they spare deeper healthy tissue. The depth of the treatment is selected by the appropriate energy. Unlike photon beams there is no surface sparing effect, so electron therapy is used when the target extends to the patient's skin.
Electron beam therapy is used in the treatment of superficial tumors like cancer of skin regions, or total skin (e.g. mycosis fungoides), diseases of the limbs (e.g. melanoma and lymphoma), nodal irradiation, and it may also be used to boost the radiation dose to the surgical bed after mastectomy or lumpectomy. For deeper regions intraoperative electron radiation therapy might be applied.
Total Skin Electron Therapy
Total skin electron therapy (TSET) is the most common treatment for mycosis fungoides (also known as cutaneous T-cell lymphoma or Sezary syndrome). The treatment involves using very large electron beams to deliver radiation to the entire skin surface. Typically this is done using six dual-beams: First, the upper portion of the patient is irradiated with one beam and then the lower portion is irradiated. Then the patient rotates one sixth of a turn and is treated with the second dual-beam. This process is repeated until the patient has been irradiated from six directions each with an upper and lower electron beam.
- Karzmark, C. J. (1987). "AAPM Report No. 23 Total Skin Electron Therapy: Technique and Dosimetry".
- Eric E. Klein: "Electron-Beam Therapy: Dosimetry, Planning, and Techniques" in: Edward C. Halperin, Carlos A. Perez, Luther W. Brady (ed.): Perez and Brady's Principles and Practice of Radiation Oncology, 5th. edition, 2008