Veterinary Radiation Therapy

Radiation therapy is an effective way to treat many kinds of cancer in almost any part of the body. 
Many veterinary patients are treated very effectively with radiation therapy for their cancers. 
Radiation may be given alone or in combination with other forms of treatment such as surgery or chemotherapy. Radiation therapy is also a very powerful pain-relieving tool and can be used in the palliative setting to significantly improve quality of life.

Sample of a three-dimensional CT based treatment plan used in the radiation planning process.  This type of planning increases the accuracy and decreases the side effects of radiation.

What is radiation therapy?

Radiation therapy is the practice of using high energy waves or particles to treat disease.  The energies used for cancer treatment are generally much higher than those used for x-ray exams.  Special equipment is used to produce and aim the radiation at the tumor area.  The most common type of machine used today in human radiation therapy is called a linear accelerator.  This is the type of radiation therapy used at the Animal Cancer & Imaging Center.

How does radiation therapy work?

Radiation kills cells by disrupting the DNA of the cell. Radiation can either kill cells or keep them from growing and dividing.  This includes tumor cells as well as normal cells of other tissues.  However, because many tumor cells are rapidly dividing, they are often more sensitive to the effects of radiation compared to normal cells.  In addition, normal cells are usually more efficient at repairing damage from radiation than tumor cells.  The goal of radiation therapy is to try to utilize these differences to destroy the tumor while minimizing damage to the normal tissues that will be included in the radiation treatment field. Like surgery, radiation therapy is a localized treatment, affecting only the area included in the radiation treatment field.

When is radiation therapy used?

Radiation therapy can be used by itself, however, it is more commonly combined with surgery and/or chemotherapy.  It may be given before surgery to shrink a tumor to a more operable size, or after surgery to stop the growth of any remaining cancer cells that the surgeon was not able to remove. The combination of treatments recommended and the sequencing of these will depend on the tumor type, the size and location of the tumor, possible side effects, as well as many other factors that we will discuss with you.

Radiation therapy may also be used for the purpose of pain relief when it is known that the cancer cannot be effectively treated by surgery, chemotherapy, or a full course of radiation therapy.  This is known as “palliative” radiation.  Just a few treatments (usually 3-6) will often relieve pain, shrink the tumor, and reduce pressure, bleeding or other symptoms of cancer.

What is the radiation treatment schedule?

The number of treatments recommended and the scheduling of those treatments are determined on an individual basis.  In general, giving many small doses increases the chances for tumor control while decreasing the likelihood for normal tissue side effects.  The treatments are typically given daily, on a Monday through Friday basis.  Your pet can be treated as an outpatient, remain in the hospital for the entire treatment course, go home on weekends, or any combination of the above.  For outpatients, you may accompany your pet to each treatment and take your pet home soon after treatment, or patients can be dropped off in the morning and picked up later in the afternoon.

What happens at each treatment appointment?

Prior to each treatment, an 8 hour fast is required.  Your pet will receive a thorough physical examination at each treatment visit.  It is important that you notify the doctor or the radiation therapist of any changes in your pet’s condition (e.g. vomiting, diarrhea, lethargy, etc.).  Your pet is anesthetized for a brief time, total anesthesia time is usually less than 15 minutes.  The actual treatment time when the radiation is being delivered is only about 2 minutes, but set-up prior to the actual treatment takes several minutes.  If you bring your pet in for the treatments, they will usually be able to go home within 30-45 minutes.  Although anesthesia carries some risk, the risk is usually minimal due to safer agents, lower doses, and short anesthesia times.  If the doctor feels that your pet has a higher risk for anesthesia due to some other medical problems, you will be informed of that risk.

What are costs involved with radiation therapy?

Treatment of cancer with radiation can be costly due to the very complex equipment and the services of many health care professionals including the veterinary oncologist, the radiation therapist, the radiation physicist, and the veterinary radiation therapy technician.  Our CT based computer treatment planning is done by Dr. Sue LaRue, Diplomate, ACVS, and ACVR (Radiation Oncology), of the Colorado State University Radiation Oncology Service.  Costs for the treatment planning vary depending on the complexity of the treatment plan and the additional services required by CSU during the treatment course.  Dr. LaRue monitors each patient closely, reviewing calculations and positioning, etc. during the course of therapy.
 
CSU has recently purchased a state of the art 3-D treatment planner.  The new equipment enables us to offer custom blocking to the computer planned patients. Custom blocking further increases our accuracy of treating the tumor and increases our ability to spare normal tissues near the treatment field.  

After your exam and the planning through CSU you will be given a treatment plan that will include the cost for the various phases of treatment.  These will vary with each patient based on their size, the details of the plan and length of treatment. Palliative courses of therapy (3-6 treatments) are typically less expensive, as they are shorter in length.  

Charges for hospitalization are separate from the radiation therapy charges and will be discussed if you plan to hospitalize your pet during radiation therapy. Overnight hospitalization is not always available on all days of the week.  Please discuss this with the doctor at the time of the consultation to determine availability.   A written treatment plan will be provided for you prior to beginning therapy.  Some types of cancer, such as certain soft tissue sarcomas or mast cell tumors on the limbs may not require port films.

What are the side effects of treatment?

Side effects of treatment in general fall into two categories: acute and late effects.  Acute effects typically start towards the middle to end of the treatment course and can continue for several weeks after.  These usually affect skin and mucous membranes in the radiation field. Late effects are those that can occur months to years after radiation and are dependent on the tissue in the radiation field. Systemic side effects are generally not seen.

ACUTE RADIATION SIDE EFFECTS:

1.) Acute radiation side effects are those side effects that occur during the treatment course or soon after radiation therapy has been completed. Acute side effects are common and generally self-limiting.  

2.) The most common acute side effect is superficial skin or mucous membrane irritation.  When the skin in the treatment field is irradiated, hair loss in the treatment field is common.  In the majority of patients, the hair will regrow but oftentimes will come in a different color.  Occasionally, hair will only regrow sparsely in the treatment field.  A more severe effect, called moist desquamation of the skin, can occur.  Treatment involves keeping the area clean and dry, keeping pets from causing self-trauma, using antibiotics if there is risk of infection, using anti-inflammatory and/or pain medication if your pet is uncomfortable.  The majority of skin side effects, even if more severe, tend to heal very quickly (usually within 1-2 weeks).  

3.) Superficial mucous membrane  damage is not uncommon, especially when the mucous membranes of the oral cavity are in the treatment field.  This side effect is called oral mucositis and will manifest as reddening/inflammation of the mucous membranes, drooling, reluctance to eat some foods, or complete anorexia.  When the radiation therapist and/or doctor notice this side effect starting, we begin medications to decrease inflammation and pain, antibiotics if there is concern for infection, and a mouthwash that has an antibiotic, anti-inflammatory, and numbing agent to help with discomfort.  At home, feeding softer, blander (especially salt-free) diets will aid in providing adequate nutrition.  In extremely rare cases, if mucositis becomes so severe that pets won't eat, the placement of a temporary esophageal feeding tube may be required.  

4.) When the ears are in the radiation treatment field, inflammation and secondary infection (otitis external or interna) can occur.  Appropriate ear medications will prescribed if this side effect is observed.

5.) When an eye is in the treatment field, acute side effects usually involve corneal irritation from radiation causing reduced tear production and subsequent dry eye. Artificial tears are recommended when this occurs.  Corneal ulcers and more severe damage are uncommon but can occur.  Blindness is rare, but cataracts later in life are commonly seen (a late side effect).  

late side effects:

1.) Late side effects are those side effects that can occur greater than 6 months to years after the completion of a radiation course.  Late term effects are a result of radiation damage to the more slowly growing tissues: connective tissues (e.g. bone, nervous tissue, cartilage), skin and eyes.  Fortunately, late term effects are rare with a likelihood of serious late effects less than 5%.  

2.) Examples of late radiation side effects include muscle fibrosis, skin fibrosis, bone necrosis (cell death) and subsequent fracture.  Radiation induced secondary cancers have been reported years after a radiation therapy course - this is also a very rare sequelae of radiation.  

3.) Because late effects can be more serious and permanent, therefore radiation dosing schemes are developed to decrease the incidence of these side effects.  Delivering a total therapeutic dose of radiation in smaller doses per treatment with more treatments is much safer than delivering the same total therapeutic dose in fewer larger doses.  Therefore, if a total dose of 48 Gy of radiation is desired, the risk of late effects would be far greater if six 8 Gy doses of radiation were given and risk of late effects would be far less if twenty sixteen 3 Gy fractions of radiation is given.  Although higher numbers of treatments at a lower dose per treatment is more expensive and time consuming, it is much safer.