Radiation therapy is used to treat cancer. Precisely targeted radiation kills the cells in the treated area while sparing the surrounding tissue as much as possible. Radiation therapy has also proven effective in relieving pain associated with osteoarthritis.
Along with surgery and chemotherapy, radiation therapy is a key pillar of tumor treatment (see related article). Depending on the severity of the disease, a distinction is made between curative and palliative treatment. The goal of curative treatment is to cure the tumor or achieve long-term control of it. If this is no longer possible, palliative treatment can slow tumor growth and improve the animal’s quality of life.
Radiation therapy is also used for the following conditions:
In veterinary medicine, linear accelerators are most commonly used as radiation therapy devices. These generate high-energy electrons (i.e., negatively charged elementary particles, components of atoms). The electrons are accelerated to high speeds and then emerge directly from the device as a beam. This allows for the irradiation of superficial tumors. To irradiate deeper-seated tumors, photons (= high-energy, massless particles of light) must be used. These are generated when the electrons in the linear accelerator first strike a tungsten plate (= a metal). The photons produced by the impact on the plate then emerge from the device as a photon beam.
The radiation used in therapy damages the DNA (=genetic material) of cells, causing them to lose their ability to divide. Radiation therapy specifically exploits the differences between healthy and tumor cells: Both healthy and tumor cells have a limited lifespan and are continuously replaced through cell division. During cell division, cells are particularly sensitive to radiation. In contrast to healthy cells, tumor cells divide frequently and, due to this high division rate, are damaged more extensively by the radiation. Although every cell possesses a repair system for damaged DNA, this system functions better in healthy cells than in tumor cells. Healthy tissue thus recovers from the radiation, while tumor cells die off.
The exact mechanisms by which radiation reduces inflammatory reactions, such as in osteoarthritis (see related article), have not yet been fully elucidated.
To precisely determine the location and size of a tumor, a planning computed tomography (CT) scan (see related article) is often performed beforehand. This is generally not necessary for the radiation treatment of a superficial tumor. The optimal positioning of your pet for radiation therapy is then determined. To ensure the exact same positioning in every radiation session, custom-made rigid head masks and vacuum cushions can be fabricated. The radiation field (the area to be treated) is calculated with a safety margin to protect vital organs. In the head region, these include the brain and the eyes.
An individualized radiation plan is then created, specifying the number of sessions and the radiation dose. The goal is to irradiate the tumor with the highest possible dose while exposing the surrounding tissue to the lowest possible dose. The radiation plan depends on the type and location of the tumor, as well as the animal’s general condition and any other existing medical conditions. Typically, five radiation sessions are held per week. For palliative treatment, in contrast to curative treatment, fewer sessions with a higher radiation dose are often used. For radiation therapy in cases of osteoarthritis, only a few sessions are required, with a dose that is very low compared to tumor radiation.
Radiation therapy is an outpatient treatment. The radiation itself lasts only a few seconds each time. To ensure precise targeting, your pet must not move. Therefore, it must be placed under brief anesthesia for each session. After monitoring the recovery phase, your pet will be discharged home.
Acute radiation reactions occur primarily during curative radiation therapy. They can develop two to three weeks into treatment. Hair loss, skin redness, and inflammation of the skin or mucous membranes may occur within the radiation field. These changes usually resolve on their own within a few weeks after the end of radiation therapy. Hair regrowth takes a little longer. It usually grows back white. Acute radiation reactions are treated, if necessary, with pain relievers and anti-inflammatory drugs, and antibiotics if needed. To protect the affected area, your pet should wear an Elizabethan collar or a protective bodysuit.
Chronic radiation reactions do not occur until months or even years after the completion of radiation therapy. They occur primarily with palliative radiation therapy. In animals with a low life expectancy due to a tumor, this is accepted as a necessary trade-off. However, treatment plans are designed so that late radiation reactions occur only very rarely. These can manifest as:
Secondary tumors can also develop very rarely as a result of radiation therapy. At the edge of the radiation field, these are usually osteosarcomas (see relevant article). Tumors can also develop in body regions that were farther away from the radiation field but were nevertheless exposed to a low radiation dose. The development time for secondary tumors is several years. Therefore, this risk is only a concern in young animals.
Since radiation is administered only locally in the area of the tumor, side effects such as nausea, dizziness, or vomiting are unlikely.
This article is for informational purposes only and does not replace veterinary advice. Please contact your veterinary practice directly.
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