Radiotherapy (radiation therapy or RT) is a therapy for cancer treatment in cats (and other species, including people). It uses high-energy x-ray beams to destroy or damage cancer cell DNA to stop it multiplying. The type of radiation used in radiotherapy is ionising radiation.
Unlike chemotherapy, which goes everywhere in the body, radiotherapy uses a beam to focus on the area of treatment.
Radiotherapy treatments are usually performed on a machine (called a linear accelerator) delivers a highly targeted beam at the cancer cells while sparing healthy surrounding tissue.
A short-acting general anesthetic is necessary for cats undergoing radiotherapy treatment as the cat must remain perfectly still to ensure the beam only targets cancer cells.
Most treatments are performed in fractions, that is, the total radiation dose is spread out over several treatments carried out over a period of days or weeks, this allows healthy cells to recover.
External beam therapy (EBT)
The most common type of radiotherapy in cats is external beam therapy (EBT). As the name would suggest, EBT focuses a highly targeted beam at the cancer cells while sparing healthy surrounding tissue.
Similar to EBT, however stereotactic radiotherapy uses higher doses of radiation to treat very small tumours in as little as one single treatment.
Not all cats are suitable candidates for frequent general anesthesia.
Intensity-Modulated Radiation Therapy (IMRT)
An newer and more advanced mode of radiation therapy which uses uses computer-controlled linear accelerators to precicely target the tumour.
Image guided radiotherapy
This treatment can be used on moving parts of the body, such as the lungs. CT imaging tracks internal movement and the beam only works when the tumour is in the exact position. This enables a higher radiation dose to be administered due to its accuracy.
Unlike other treatments, brachytherapy is the insertion of radioactive implants directly to the targeted area.
When is radiotherapy used?
Radiotherapy can be used in the following ways.
- Preoperative: Before cancer surgery to shrink the tumour.
- Postoperative: After cancer surgery to kill any remaining cancer cells.
- Primary definitive: As a standalone treatment when surgery isn’t possible due to anatomy, such as the brain, oral cavity, bone, upper jaw and nasal cavity or to treat superficial tumours such as soft tissue and mast cell tumours.
- Chemoradiation: Some treatments combine radiotherapy and chemotherapy, without surgery.
- Palliative: To slow down progress of a tumour which can not be surgically removed and/or relieve pain and discomfort of a tumour.
What happens before and during treatment?
Your veterinarian will refer your cat to a specialist centre who have both the necessary equipment and a radiation oncologist.
- Baseline tests: Complete blood count, biochemical profile and urinalysis are performed to evaluate the overall health of the cat and assess its suitability for radiotherapy.
- CT scan: This advanced imaging technique is performed to evaluate the size and shape of the tumour and to evaluate for metastasis (spread of the tumour to other parts of the body). A CT scan enables the veterinary oncologist to match the size and shape of the beam to the size and shape of the tumour, to minimise damage to nearby tissue. The CT scan helps the veterinarian to formulate a treatment which will determine the dose and frequency.
Cats can be treated as inpatients, or return home between treatments. Inpatients have the advantage of not having to travel to and from the veterinary hospital.
Prior to the start of treatment, the area is shaved, to allow better penetration of the beam.
The treatment itself lasts between 10 and 20 minutes.
- The cat is given sedation and anesthesia, a breathing tube is inserted.
- The cat is placed on the linear accelerator, placed in position and the area marked to align the cat with the radiation beam.
- Images are taken to check the cat is properly aligned.
- Radiotherapy commences, which lasts 10-20 minutes.
- Once radiotherapy is finished, the cat moves to recovery where it is given drugs to reverse the anesthetic and the breathing tube is removed.
The treatment itself delivers a painless beam to the target area. The strength of the beam is considerably lower than that used to treat human cancers.
Early side effects:
Over the course of the multiple treatments, the skin can become dry, itchy, irritated and blistered. Other side effects include lethargy, hair loss, conjunctivitis and mucositis (inflammation of the mucus membranes) and esophagitis (inflammation of the esophagus).
Late side effects:
Permanent hair loss, scars and cataracts.
Is radiation treatment expensive?
Yes, it can cost several thousand dollars to treat a cat.