Equis ISSN 2398-2977


Synonym(s): Radiation, brachytherapy

Contributor(s): Cody Coyne, Prof Derek Knottenbelt, Anna Hollis


  • Ionizing radiations used for therapeutic purposes in veterinary medicine include:
    • Beta radiation (high energy electrons).
    • Gamma radiation (electromagnetic radiation).
    • Applied by brachytherapy or more rarely in horses by teletherapy.
    • Currently teletherapy is not used to any extent in equine medicine but few reports of individual cases support value of procedure.
See Radiotherapy: radiation sources table.
  • Exposure to ionizing radiation kills cells by producing secondary charged particles and free radicals in the nucleus.
  • These cause different types of DNA damage and prevent successful mitosis.
  • Radiation damages both normal and tumor cells, but normal cells are better able to repair radiation damage, and can usually repair and function normally, whereas tumor cells will die in response to appropriate doses of ionizing radiation.
  • Other structures may be involved in the response of tissue radiation, such as proteins and lipids in the cell membrane, and radiation may also lead to exposure of the immune system to abnormal epitopes, encouraging a pro-inflammatory, tumor-specific immune response, contributing to tumor regression.
  • Different cells have different sensitivity to radiation, mostly because of differences in the rate of cell division; cells that are actively dividing will be damaged by much lower doses of radiation than those required to destroy a well-differentiated cell.
  • Early unwanted effects of radiation can be seen within a few weeks of the completion of a treatment course, and may include skin erythema, desquamation of the skin, and depigmentation.
  • Late unwanted effects may be seen many months or years after radiotherapy, such as fibrosis, bone necrosis, and (in periocular locations) cataract formation


  • Ionizing radiation of tumor masses.


  • Very effective.
  • Slow effects (easier to prevent excessive regional cytotoxic effects).
  • Good cosmetic effects.
  • More effective in fast dividing cells.


  • Operator exposure (occupational hazard).
  • Cost.
  • Availability.
  • Logistics.
  • Non-discriminatory (normal cells are also affected) can have serious effects on rapid dividing cells such as bone marrow and testicular cells during treatments for slower growing masses (such as keratinocytes or fibroblasts) where treatment is given local to these, although shielding and careful planning minimizes these effects.
  • Administrative: long inventory and accountability.


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  • Excellent where correct doses and methods are used and the whole tumor can be radiated.

Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Bradley W M, Schlipp D & Khatibzadeh S M (2015) Electronic brachytherapy used for the successful treatment of three different types of equine tumours. Equine Vet Educ 29 (6), 293–298 WileyOnline.
  • Burks B S, Leonard J M, Orsini J A & Trombetta M (2009) Interstitial brachytherapy in the management of haemangiosarcoma of the rostrum of the horse: case report and review of the literature. Equine Vet Educ 21 (9), 487-493 VetMedResource.
  • Byam-Cook, Henson F M & Slater J D (2006) Treatment of periocular and non-ocular sarcoids in 18 horses by interstitial brachytherapy with iridium-92. Vet Rec 159 (11), 337-341 PubMed.
  • Henson F M D & Dobson J M (2004) Use of radiation therapy in the treatment of equine neoplasia. Equine Vet Educ 16 (6), 315-318 VetMedResource.
  • Knottenbelt D C & Kelly D F (2000) The diagnosis and treatment of periorbital sarcoid in the horse: 445 cases from 1974-1999. Vet Ophthal 3 (2), 73-82 PubMed.
  • Theon A (1998) Radiation therapy in the horse. Vet Clin N Am Equine Prac 14 (3), 673-688 PubMed.
  • Knottenbelt D C, Edwards S E R & Daniel E A (1995) The diagnosis and treatment of the equine sarcoid. In Pract 17 (3), 123-129 VetMedResource.
  • Blackwood L & Dobson J M (1994) Radiotherapy in the horse. Equine Vet Educ 6 (2), 95-99 VetMedResource.
  • Theon A P & Pascoe J R (1994) Iridium-192 interstitial brachytherapy for equine periocular tumours: treatment results and prognostic factors in 115 horses. Equine Vet J 27 (2), 117-121 PubMed.
  • Walker M A, Adams W et al (1991) Iridium-192 brachytherapy for equine sarcoid, one and two year remission rates. Vet Radiol 32 (4), 206-208 VetMedResource.
  • Walker M A, Goble D & Geiser D (1986) Two-year non-recurrence rates for equine ocular and periorbital squamous cell carcinoma following radiotherapy. Vet Radiol 27 (5), 146-148 VetMedResource.
  • Turrel J M & Koblik P D (1983) Techniques of afterloading iridium-192 interstitial brachytherapy in veterinary medicine. Vet Radiol 24 (6), 278-283 VetMedResource.
  • Frauenfelder H C, Blevins W E & Page E H (1982) 90Sr for treatment of periocular squamous cell carcinoma in the horse. J Am Vet Med Assoc 180 (3), 307-309 VetMedResource.
  • Baker J R & Leyland A (1975) Histological survey of tumours of the horse with particular reference to those of the skin. Vet Rec 96, 419-422 PubMed.

Other sources of information

  • Knottenbelt D C, Patterson-Kane J C & Snalune K L (2015) Clinical Equine Oncology. Elsevier, London.
  • Scott D W (2003) Dermatologic Therapy. In: Equine Dermatology. W B Saunders, Philadelphia, USA. pp 187-188.