All About Radiation Therapy – Cancer Treatment in Pets
November 11, 2020
What is radiation therapy for cancer treatment in pets?
Radiation, as a cancer treatment for pets, can be broadly divided into electromagnetic and particulate radiation. Electromagnetic radiation is a form of energy that is present all around us and takes many forms including radio waves, microwaves, infrared (visible) light, ultraviolet, x-rays and gamma rays.
The form of radiation used in cancer therapy is a high-energy type referred to as ionizing radiation. Ionizing radiation is a type of energy released by atoms that travel in the form of electromagnetic waves (gamma or x-rays) or particles (neutrons, beta or alphas).
Normally, cells will grow and divide to form new cells. Cancer cells also grow and divide to form other cancer cells but do so faster. Radiation works by damaging the DNA (causing small breaks in the genetic material) in tumor cells. This process causes disruption of their growth and cell division resulting in tumor cell death. Nearby normal cells can also be affected by radiation, but most recover and continue to work the way they should.
Radiation therapy does not kill cancer cells right away. It can take days or weeks of treatment before tumor cell death can occur. When the damaged cells die, they are broken down and removed by the body.
How is radiation therapy given?
The most common type of radiation therapy used to treat cancer in companion animals is external beam radiation. A machine is used to aim radiation beams at the pet’s tumor or surgical scar while avoiding as much normal tissue as possible. Most pets are placed under general anesthesia for each treatment and carefully positioned on a treatment table. A CT scan (cat scan) is typically used prior to initiation of radiation therapy. This allows us to determine the extent of the tumor and to devise a pet-specific radiation therapy plan.
Types of external beam radiation therapy
The ways in which radiation therapy can be planned and delivered include:
- Photon beam radiation therapy: usually known as external beam radiation therapy. It uses photon beams to get to the tumor and is given by a machine called a linear accelerator.
- Three-dimensional conformal radiation therapy (3D-CRT): involves multiple radiation beams that are “sculpted” around the tumor target based on CT images.
- Intensity modulated radiation therapy (IMRT): is an advanced form of high precision radiation therapy that modulates (adjusts) the intensity of the radiation beam across the treated field. This is accomplished with the aid of a multi-leaf collimator system moving in and out of the beams allowing the dose of radiation to vary within a single beam. With this type of radiation therapy, high-energy X-rays can be directed at a patient’s tumor while minimizing complications to surrounding healthy tissue.
- Stereotactic radiation therapy (also known as stereotactic radiosurgery): uses highly conformal and focused irradiation beams directed precisely at a target and is typically delivered over 1-5 closely scheduled doses.
- Image guided radiation therapy (IGRT): uses images of the patient at the time of treatment to determine the accuracy of setup so that corrections can be made in real time before the treatment is delivered.
Common tumors treated with radiation therapy
The most common tumors treated with radiation therapy include the following:
- Brain tumors
- Nasal tumors
- Oral tumors
- Soft tissue sarcomas
- Mast cell tumors
- Injection site associated sarcomas (also known as vaccine associated sarcomas)
- Prostate tumors
- Anal sac tumors
- Bone tumors
What are the most common types of radiation therapy protocols?
- Definitive intent radiation therapy (RT): This type of radiation therapy uses a small fraction (dose) of radiation administered on a daily basis (Monday thru Friday) over a 3 to 4 week period under general anesthesia. The primary goal of this type of therapy is to achieve long term tumor control (often >1 year depending on the tumor type) while minimizing side effects. Definitive intent radiation therapy is often used after surgery for incompletely excised tumors aiming for the best chance at local tumor control. In some cases, it may be used prior to or as an alternative to surgery.
- Palliative radiation therapy: The main goal in palliative RT is to relieve pain or improve function particularly in patients with advanced cancer. With this type of radiation therapy, control of the tumor is typically shorter when compared to definitive radiation therapy. These protocols can vary and may involve weekly treatments or treatments given over the course of a few days.
What are the potential side effects that can be seen with radiation therapy?
Radiation therapy (RT) in our companion animals is generally well tolerated. Radiation therapy plans are created with the emphasis of maximizing quality of life while minimizing side effects. These side effects are dependent on the type of radiation applied, location of the tumor and RT treatment field.
When radiation therapy side effects occur, they are generally divided into early (acute) and late side effects.
Acute side effects occur in tissues that have a normal rapid cell turnover such as epithelial linings (i.e. skin, mucous membranes and gastrointestinal tract). These side effects typically occur half way through radiation and can last for a few weeks after RT. These include hair loss (alopecia), irritation of the skin, mucositis, conjunctivitis and dry eye.
Radiation therapy can also cause effects that are delayed by many months to even years (referred to as late side effects) and are not expected to resolve. Late side effects occur in tissues where cell division is slow such as bone and nervous tissue.
Acceptable late side effects include hair loss, skin hyperpigmentation and cataracts. More serious late side effects include bone necrosis, skin fibrosis and nervous tissue atrophy or necrosis. These side effects are considered rare in general but preventative measures are taken to avoid these effects especially in patients expected to have a long-term survival.
How is radiation used with other cancer treatments?
In some cases, radiation therapy may be the only treatment needed. But, most often, pets will have radiation with other treatments such as surgery, chemotherapy and/or immunotherapy. Radiation therapy can be given before, during, or after these treatments. The timing of when radiation therapy will be administered depends on the type of cancer being treated as well as the goal of radiation (definitive vs palliative).
The Cancer Center at AVCC is located in South Florida in Broward County.
8920 W. State Road 84,
Davie, Florida 33324
The Cancer Center at AVCC offers the following oncology services:
Diagnostic tests including:
- Fine needle aspirates/cytology
- Bone marrow aspirates
- Bone biopsies
- Incisional and punch biopsies
- Personalized genomic testing
- Traditional chemotherapy (intravenous/intracavitary)
- Metronomic chemotherapy
- Targeted chemotherapy
- Palliative care and pain management
- Hospice counseling
- Nutritional counseling and referral
- Referral for pet radiation therapy
For more on cancer treatment for your pet, see our Comprehensive Guide to Pet Cancer Care.
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