Radiation Oncology

Stereotactic radiation therapy (SRT) is a method of delivering a curative dose of radiation therapy with very few treatments.

Conventional radiation treatments can take many weeks as where SRT can be done within a few days. The planning and treatments are much more complex than conventional treatments, leading to less normal tissue being irradiated and much less intense side effects.

SRT provides an alternative to surgery as the tumour needs to be intact for this type of treatment. Your radiation oncologist will let you know if your pet is eligible for SRT.

Radiation therapy works by damaging the DNA within cancer cells and destroying the ability of the cancer cells to reproduce. When these damaged cancer cells die, the body naturally eliminates them. Normal cells are also affected by radiation, but they are able to repair themselves in a way that cancer cells cannot.

Sometimes radiation therapy is the only treatment a patient needs, and other times it is only one part of a patient’s treatment. For example, non-resectable brain tumours are often treated with radiation alone, but a dog or cat with a soft tissue sarcoma may be treated with surgery, radiation therapy and chemotherapy.

Sometimes radiation therapy is used as adjuvant therapy to make your pet’s primary treatment more effective. For example, your pet can be treated with radiation therapy (the adjuvant treatment) before surgery (the primary treatment) to help shrink the cancer and allow less radical surgery than would otherwise be required, or your pet may be treated with radiation after surgery to destroy microscopic cells that may have been left behind.

A veterinary radiation oncologist may choose to use radiation therapy in a number of different ways. Sometimes the goal is to cure the cancer. In this case, radiation therapy may be used to:

• destroy tumours that have not spread to other parts of your pet’s body
• reduce the risk that cancer will return after your pet undergoes surgery or chemotherapy by killing tiny cancer cells that may remain.

• shrink tumours that are interfering with your pet’s quality of life, such as a tumour in the mouth that is interfering with your pet’s ability to eat
• alleviate pain caused by a cancer such as a painful bone tumour.

It is important for you to discuss the goal of your pet’s treatment with your veterinary radiation oncology team.

Radiation oncologist

Your radiation oncologist will also monitor your pet’s progress and adjust the treatment as necessary to make sure the radiation is hitting its target while minimizing side effects. Before, during and after your pet’s radiation therapy treatments, your radiation oncologist works closely with other veterinarians, such as internal medicine specialists and surgeons, to maximize the radiation's effectiveness.

Clinical associate

The clinical associate is a veterinarian who oversees your pet’s care and management during the radiation therapy. She assists the radiation oncologist with consultations, post-treatment check-ups and record the daily progress of each patient. The clinical associate also acts as a liaison between the radiation therapy team, the referral veterinarians and the clients. 

Radiation therapist

The radiation therapist is responsible for the technical aspects of the treatment. This team member designs the immobilization equipment, performs the CT simulation scan, assists the radiation oncologist with treatment plans and administers the daily treatments.

Because your pet needs to be anesthetized for each treatment, the radiation therapist will work closely with an anesthesia veterinary technician that will anesthetize and monitor the patient during the actual treatment. The radiation therapist's responsibilities also include doing daily quality control tests to ensure the equipment is in proper working order.

Medical physicist

Qualified medical physicists help to ensure that complex treatments are correct and properly tailored for each patient.

Medical physicists are responsible for developing and directing quality control programs for equipment and procedures. Their responsibilities also include ensuring that the equipment works properly by taking precise measurements of the radiation beam and performing other safety tests on a regular basis.

• VMC Oncology Team Members

It is important that you fully understand the potential benefits, side effects and goals of radiation therapy for your pet. Your veterinary radiation oncologist and radiation therapist are available to answer any questions you may have during your pet’s treatment.

Coping with a diagnosis of cancer for your dog or cat and researching the various treatment options can be a stressful experience. To assist you in this process, below is a list of questions you may want to ask your radiation oncologist if you are considering radiation therapy for your pet.

• What type and stage of cancer does my pet have?
• What is the purpose of radiation treatment for my pet’s type of cancer?
• How will the radiation therapy be administered? Will the treatments hurt?
• For how many weeks will my pet receive radiation? How many treatments will they receive per week?
• What are the chances that radiation therapy will work?
• What is the chance that the cancer will spread or come back if my pet does not have radiation therapy?
• Will my pet need chemotherapy, surgery or other treatments? If so, in what order will they receive these treatments, and how soon after radiation therapy can they start them?
• How can I expect my pet to feel during treatment and in the weeks following radiation therapy?
• Will my pet be able to continue with their normal activity level?
• What side effects may occur from the radiation and how are they managed?
• Do I need to take any special precautions, like keeping my pet out of the sun or avoiding certain diet supplements?
• Does my pet need a special diet during or after their treatment?
• Will side effects change my pet’s appearance? If so, will the changes be permanent or temporary? If temporary, how long will they last?
• How often do I need to return for checkups for my pet?
• How and when will you know if my pet is cured of cancer?
• What are the chances that the cancer will come back?
• What are the costs associated with radiation therapy for my pet?

Consultation with a veterinary radiation oncologist

If you are considering radiation therapy as a treatment option, you must first schedule a visit with a veterinary radiation oncologist to see if radiation therapy is right for your pet. Before a consultation can be booked, your family veterinarian must submit a veterinary oncology referral form to the WCVM Veterinary Medical Centre.

After reviewing your pet’s medical tests (including radiographs, CT scans and MR scans) and completing a thorough examination, your radiation oncologist will fully discuss with you the potential benefits and risks of radiation therapy for your pet and answer your questions.

Radiation treatment planning

To be most effective, radiation therapy must be aimed precisely at the same target or targets each and every time treatment is given. The process of measuring your pet’s anatomy and determining landmarks to help your team direct the beams of radiation safely and exactly to their intended locations is accomplished with a special treatment planning CT scan. This CT scan may be in addition to your pet’s diagnostic CT scan.

During the treatment planning CT, your radiation oncologist and radiation therapist will place your pet in the exact position that he/she will be in during the actual treatment. This may require an immobilization device to be constructed. Your pet’s radiation therapist then places marks that help locate the area to be treated directly on your pet’s skin or onto the immobilization device. The radiation therapist marks your pet’s skin with a bright, temporary paint or a set of small permanent tattoos.

Once a treatment planning CT scan is done, sophisticated treatment-planning computer software is used to help design the best possible treatment plan. After reviewing all of this information, your doctor writes a prescription that outlines the exact course of your pet’s radiation therapy treatment.

Pre-treatment care instructions

Your animal will undergo a short general anesthesia with every treatment. The night before radiation therapy, your pet needs to be fasted from 10:00 p.m. on. This means they can have no food beyond this time.They can still have water available to them until 8 a.m. the morning of treatment — at which time water must be taken away as well.

When your pet undergoes external beam radiation therapy treatment, each session is painless, like getting an X-ray. The radiation is directed to your pet’s tumour from a machine located outside of their body. One of the benefits of radiation therapy is that it is usually given as a series of outpatient treatments and your pet may be able to return home each afternoon after they have recovered from the general anesthetic.

Treatments are usually scheduled five days a week, every day except Saturday and Sunday, and continue for three to five weeks. Other times, only one or a few treatments are required, such as for the treatment of cancer that has spread to the bone. The number of radiation treatments you will need depends on the size, location and type of cancer your pet has, their general health and other medical treatments they are receiving.

Your pet will undergo a short, general anesthesia to make sure that they remain completely still during the treatment. The effects of the anesthetic drugs will have mostly worn off by the time your pet goes home each day, but they may still sleep more than usual or act slightly differently.

The radiation therapist will administer your pet’s external beam treatment following the radiation oncologist’s instructions. It will take about 10 to 20 minutes for your pet to be positioned for treatment and for the equipment to be set up. Once your pet is positioned correctly, the therapist will leave the room and go into an adjoining control room to closely monitor your pet on a television screen while administering the radiation. There is a microphone in the treatment room and video monitors so your pet can be closely watched. The machine can be stopped at any time if needed.

The radiation therapy team carefully aims the radiation to decrease the dose to the normal tissues surrounding the tumour. Still, radiation will affect some healthy cells. The time in between daily treatments allows your pet’s healthy cells to repair much of the radiation damage. Most dogs and cats are treated on an outpatient basis, and many can continue with their normal activity level.

Sometimes a course of treatment is interrupted for a day or more. This may happen if your pet develops side effects that require a break in treatment. Adding treatments at the end of your pet’s protocol may be recommended to make up missed treatments. Try to bring your pet on time and avoid missing any of your appointments.

Your radiation oncologist monitors your pet’s daily treatment and may alter their radiation dose based on these observations. Your radiation oncologist may also order blood tests, X-ray examinations and other tests to see how your pet’s body is responding to treatment.

Weekly status checks

During radiation therapy, your radiation oncologist and radiation therapist will see you regularly to discuss your pet’s progress and any side effects they are experiencing, and to recommend treatments for those side effects (such as medication) and address any questions you may have. As treatment progresses, your doctor may make changes in the schedule or treatment plan depending on your pet’s response or reaction to the therapy.

Imaging protocols

During treatment, your pet’s radiation therapist will routinely use the treatment machines to take special X-rays called port films. Your pet’s treatment team routinely reviews these films to be sure that the treatment beams remain precisely aimed at the proper target. These X-rays are not used to evaluate your pet’s tumour.

Follow up

After treatment is completed, follow-up appointments will be scheduled so that your pet’s radiation oncologist and your veterinarian can make sure their recovery is proceeding normally and can continue to monitor their health status. You will also be contacted by phone to discuss your pet’s progress. Reports on your pet’s radiation treatment will be sent to your veterinarian.

As time goes on, the frequency of your pet’s visits will decrease. However, you should know that your radiation oncology team will always be available should you need to speak to someone about your pet’s treatment.

Side effects usually begin by the second or third week of treatment, and they may last for several weeks after the final radiation treatment. In rare instances, serious side effects develop after radiation therapy is finished. Your radiation oncologist and radiation therapist are the best people to advise you about the side effects your pet may experience. Talk with them about any side effects your pet is having. They can give you information about how to manage them and may prescribe medicines that can help relieve your pet’s symptoms.

General side effects from radiation that most pets receiving daily treatments will experience include skin changes, mild fatigue and a decrease in appetite.

Skin changes

Side effects of radiation therapy are limited to the area that is receiving treatment. After about two to three weeks of treatment, your pet’s skin will start to show side effects from the therapy. Skin side effects will usually be at their worst about two weeks after the radiation protocol is over. These side effects will get worse before they get better.

Cats generally have mild skin changes compared to dogs. Most skin reactions will go away several weeks after treatment is finished. In most cases, though, the treated skin will change colour permanently. Hair regrowth may take months and may remain sparse. Your pet’s hair will usually regrow in a different colour. Depending on your pet’s specific treatment, the following changes can happen to his or her skin:

• reddening (like a sunburn)
• temporary and/or permanent hair loss in the treatment area. Your pet may also be shaved for the treatments in order to help position him or her accurately from day to day
• dryness and itchiness
• blistering in the treatment area that may lead to oozing or bleeding.

Because of these side effects, we recommend:

• Do not use any soaps, lotions or creams on your pet’s skin in the area we are treating unless directed otherwise. Many skin products can leave a coating on the skin that may cause irritation and some can interfere with penetration of radiation into the body.
• It is important to keep the area clean, so gently rinse the area with lukewarm water if necessary (for muddy paws, etc.) Gently pat to dry. Do not rub.
• Please do not put any bandages, collars or clothing on the treated area. Your pet’s radiation treatment staff will monitor your pet’s side effects at each treatment, and will let you know if bandaging is recommended (for oozing or bleeding).
• Your pet may need to wear an Elizabethan collar (“cone”) if he is licking the area.
• Avoid direct exposure of the treated area to the elements (sun, wind, cold, snow) as much as possible.
• If we are treating your pet’s leg or paw, clear an area of mud and snow for bathroom breaks during the winter. This will help prevent irritation to the skin we are treating.
• Do not apply direct heat or cold to the treatment area.
• Protect your pet’s skin in the treated area from the sun for the rest of his or her life if the area is not covered by hair (or does not re-grow hair).

Fatigue

Tiredness is common from radiation treatments and general anesthesia; your pet may not seem as alert and active as usual. He or she may want to sleep more often — this is normal. Your pet may also be "moody" from this tiredness (and from the added stress of being away from home). This might make him or her less tolerant of children or other pets, for example. Your radiation therapist or radiation oncologist will advise you if there are any activity restrictions for your pet.

Loss of appetite

It is very common for pets with cancer to experience a loss of appetite, even before treatments begin. This is so common that it has a special name: cachexia.

It is important that your pet does not lose a lot of weight (more than five per cent of its starting body weight) while on treatment. This is so your pet's body can put energy into healing their normal cells.

Some things that can help your pet to eat more include:

• divide your pet’s total daily food into three to five equal amounts, and feed these at different times throughout the day (instead of larger sized meals)
• vary the foods you offer your pet through the day
• make sure your pet has access to water at all times
• avoid coarse foods such as raw vegetables and popcorn if your pet’s mouth or neck is in the treatment field
• do not offer them foods or fluids that are very cold or very warm
• chicken breasts, tuna fish and strongly scented foods that have been warmed up will encourage a reluctant eater
• gently stroking your cat or dog while offering them food may encourage them to eat
• it may help to increase your pet’s protein intake during treatments. Dietary supplements may help increase protein, but please talk to your radiation therapist or radiation oncologist before giving them to your pet.

Talk to your therapist or oncologist if your pet is having difficulty eating and these suggestions do not help. A prescription may be given to ease discomfort or stimulate appetite.

Your radiation treatment team will discuss your pet’s diet with you if any changes are recommended. Acupuncture may help with discomfort from side effects and increase your pet's appetite during radiotherapy.

Ensure that they get plenty of rest. Many pets experience mild fatigue during radiation therapy, so it is important to make sure they have quiet times to rest in a comfortable environment during the day.

Feed your pet a balanced, nutritious diet. Offer your pet tasty, easily digested foods. Low sodium, softer foods that have a strong smell and have been warmed up may help increase your pet’s desire to eat. Cats often enjoy fish-flavoured canned foods, tuna fish and chicken breast. The radiation oncologist may prescribe a medication to enhance your pet’s appetite. Your pet’s weight will be monitored closely during their treatment and a feeding tube may be recommended if they experience soreness that interferes with their desire to eat.

Treat the skin that is exposed to radiation with extra care. The skin in the area receiving treatment may become red and sensitive. The radiation therapist will review specific instructions for caring for your pet’s skin with you. Some guidelines include:

• avoid using any lotions or any other products in the treatment area unless approved by your radiation oncologist or radiation therapist
• avoid putting anything hot or cold on your pet’s treated skin. This includes heating pads and ice packs
• protect the treated area from the sun. If possible, avoid exposing the treated area to the sun altogether.

The desired benefits can include a reduction in the size of the tumour, thus providing temporary relief of such symptoms as pain or other tumour complications that cause suffering. Palliative radiation therapy would not, therefore, be considered as an option if either cure or long-term remission could be obtained through a more intensive protocol. Nor would radiation be offered as a palliative therapy if a pet were considered too critically ill to benefit.

During "external beam radiation therapy," a beam of radiation is directed through the skin to the tumour and the surrounding area in order to kill whatever cancer cells it encounters. The desired effect is that growth of the tumour is slowed, and the symptoms the tumour was causing are reduced, at least for a time.

The machine used to deliver external beam radiation therapy at the WCVM Veterinary Medical Centre is a Varian Cliniac 21EX linear accelerator (otherwise known as a LINAC). It uses high energy X-rays to produce either photon or electron beams.

Your pet will be precisely positioned on the treatment bed using laser guidance so that the beam passes through the tumour. The beam dimensions as well as the radiation dose are tailored to your pet’s need. Normal tissue exposure is limited as much as possible by using advanced software programs.

Receiving external beam radiation therapy is somewhat similar to having an X-ray taken. A short general anesthetic is used to prevent the patient from moving during treatment. During treatment, the machine itself never touches your pet nor does it leave your pet in a radioactive state after the radiation beam is turned off.

Treatment protocol

The treatment protocol for palliative therapy varies depending on the particular cancer. In some cases, a single dose provides benefit. In other situations, radiation yields a better response when the dose is administered on two consecutive days, or over a period of 28 days with a week or two between treatments. Hospitalization is not typically required. Patients are free to return home as soon as recovery from the anesthesia is complete.

Side effects

Palliative radiation generally produces minimal side effects. Your pet could seem a little tired after treatment, as a result of the anesthetic and the stress he or she might be feeling from the change in routine. As well, if your pet’s symptoms include pain, this could seem a little more pronounced for a day or so after treatment, primarily due to the positioning we must use on the hard treatment table. Occasionally, the skin can become slightly reddened and lose hair, but this will happen only in the area being treated. Temporary swelling of the tissue in the area can also occur.

Outcome

The desired outcome of using radiation in your pet’s particular case will be discussed with you in detail prior to the initiation of treatment. Most patients will demonstrate some improvement in their symptoms within one to two weeks after receiving radiation. Improvement could continue to increase for up to one month after treatment. The length of response varies depending on the patient and the cancer involved. If the patient shows a good response after his or her treatment, additional doses can be given on an as-needed basis.

Palliative radiation will not prevent spread of the cancer from the primary site of disease. Nor will it necessarily increase the length of time that your pet will continue to be with you. The goal of palliative radiation therapy is to increase your pet’s sense of comfort and well-being, and thus improve his or her overall quality of remaining life.

Adjuvant treatment: A treatment that is given in addition to the primary treatment to enhance its effectiveness and reduce the chance of the tumour recurring.

Blocks: Pieces of metal alloy that can be used to shape the radiation beam.

Bolus: Pieces of soft material placed on the patient’s skin during treatments.

Boost: An additional dose of radiation that is given after an initial course of radiation to enhance tumour control. A boost may be given to the tumour and areas to which the tumour may have spread.

Brachytherapy: Internal radiation therapy that involves placing radioactive sources inside or adjacent to the tumour.

Cancer: A group of diseases in which abnormal cells divide uncontrollably, forming a tumour or mass. Cancerous tumours can invade and destroy healthy tissue. They can also spread to other parts of the body, forming new tumours or metastases.

Catheter: A tube inserted into the vein that can be used to deliver drugs and fluids, often placed during anesthetic procedures.

Clinical trials: Studies that test new cancer therapies.

CT or CAT scan: A computer assisted tomography scan is an X-ray procedure that uses a computer to produce detailed pictures of the body.

General anesthesia: Using anesthetic drugs to put an animal in a state of total unconsciousness.

Immobilization device: A device that is used to help a patient remain in the same position during every treatment.

Local anesthesia: Using injection of a drug to create a loss of sensation in a small area of the body (as when a local anesthetic is injected for a tooth extraction).

Metastases: Cancer that has spread from one part of the body to another, such as from the mouth to the lymph nodes or lungs.

MR or MRI scan: A magnetic resonance imaging scan is a procedure that uses a magnetic field to create detailed pictures of the body, often used to create pictures of the brain or spinal cord.

Palliative care/palliation: Treatment that is intended to relieve symptoms, but not cure disease.

Port films: Port films are pictures of the position of the radiation beams used to treat cancer. They are used to verify the position of the beams and confirm that treatment is delivered to the right place.

Radiation oncologist: A veterinarian who specializes in treating cancer and other diseases with radiation therapy.

Radiation oncology: The medical specialty that deals with treating cancer and other diseases with radiation.

Radiation therapy: The careful use of various forms of radiation to treat cancer and other diseases.

Radioprotector: A type of drug that protects normal tissues in the area being treated.

Radioresistant: A term used to describe a tumour that does not respond well to radiation therapy.

Radiosensitizer: A type of drug that can make a tumour respond better to radiation therapy.

Systemic radiation therapy: The use of radioactive isotopes that can travel throughout the body to treat certain cancers.

Treatment plan: A radiation oncologist’s prescription describing how a patient should be treated with radiation therapy. The radiation oncology team uses sophisticated treatment planning software to maximize radiation to the tumour while sparing healthy tissue.

Tumour: An abnormal lump or mass of tissue.