Radiotherapy

Cats today are healthier and, in general, living longer than ever before. However, the increasing numbers of ageing cats mean that they are at increasing risk of developing cancer later in life. It can be very frightening when you hear that your cat has cancer, but veterinary care has advanced rapidly over recent years and there may well be an effective treatment for your cat.

Radiotherapy uses radiation (like a powerful type of x-ray) to damage and destroy cancer cells. The radiation can be administered in a number of ways but when it contacts cells it causes permanent damage. Most commonly radiation is delivered from an external source, for a short period of time, on a regular basis (external beam therapy). Radiation delivered in high doses can do damage very rapidly so a short exposure to the radiation beam will damage the cells which then die off over the next few days to months. Most cancer cells, treated with radiotherapy, will die when they divide. Therefore, the length of time that this takes to happen depends on the tissue type. Rapidly dividing tissue (such as the intestinal lining) will have their cancer cells dying quickly, but slowly dividing tissue (such as nerve or bone) will take longer.

The aim of radiotherapy is to give a high dose of radiation to the cancer cells (doing maximum damage) whilst minimizing the dose to the rest of the body.

It is quite expensive to have radiotherapy, and you will have to travel to a specialist center to get treatment, so your veterinarian will not recommend the procedure unless they think it is likely to help in the treatment of your cat. Cancers can be treated using surgery, drugs (chemotherapy), electrochemotherapy, immunotherapy, radiotherapy or often a combination of these. Radiation therapy can be used directly on a cancer mass or after surgery, if the mass has been incompletely removed. Each type of cancer is best treated in a particular way and if your veterinarian has recommended one form of treatment it is likely that this is the best option for your cat. However, if you are concerned about the treatment then discuss your worries with your veterinarian.

Radiotherapy is usually given as a course of treatments. It is very important that all treatments in the course are given at the right time so make sure, before agreeing to treatment, that you can take your cat for every session. Most radiotherapy centers offer boarding for cats for the whole length of the treatment course, so this may be something to ask about if need be. The damage to cancer cells caused by radiotherapy builds up over time so each treatment kills off cells missed by the previous one. The time between each treatment in the course allows the normal healthy tissues to recover and grow. So the course maximizes the damage to cancer cells whilst reducing the risk of side effects.

Many owners are worried by the idea of radiotherapy for their cat because they have heard of the side-effects suffered by human cancer patients. In people the aim of cancer treatment is to kill all cancer cells and cure disease. Doses of radiotherapy for people are therefore high and side-effects such as fatigue, skin changes, vomiting and hair loss are relatively common. Although it does sometimes cure cancer, the aim of cancer treatment in cats is to prolong a good quality of life (rather than necessarily trying to cure the cancer). This means that treatment sessions are designed to have the maximum beneficial effect without causing severe side effects. Your cat should remain well throughout the course of treatment. If side effects develop, they are generally acute and resolve within 2–3 weeks after completion of the course.

If your cat is having external beam radiotherapy, the radiation does not stay in their body, which means they are able to come home between treatments. However, it is very important that the treatment is delivered at regular intervals and so if the treatment interval is short, eg daily or alternate days, your vet may recommend that they stay in hospital so that you do not have to keep travelling back and forward.

It is essential that your cat remains still throughout the whole treatment as this must be directed at a very specific area of the body. Severe damage can be caused if the radiation beam strikes the wrong tissue during the procedure.

Modern anesthetics are very safe, and your cat will probably recover more rapidly from an anesthetic than any form of sedation. As radiotherapy is usually performed at specialist centers it is likely that your cat’s anesthetic will be monitored by a veterinarian with a special interest in anesthesia and the anesthetic will be very safe. You will usually be able to take your cat home as soon as they have recovered from the anesthetic unless they are receiving further treatment.

As your cat will be having an anesthetic, your veterinarian will ask you to not feed your cat for a specified amount of time. Occasionally drugs are given before treatment to increase the effect of the radiation on cancer cells if your veterinarian gives you specific instructions make sure you follow them carefully.

There is a small risk associated with repeated anesthetics, but your cat’s health will be closely monitored, and modern anesthetics are very safe.

Radiotherapy is a very powerful treatment! The aim is to give a dose that will destroy most of the cancer cells whilst allowing the normal tissue to recover between treatments. Some cells are very sensitive to the effects of radiation so when treatment is planned your veterinarian will try to avoid particularly sensitive areas (such as the eye). Side effects may develop in the treatment field, they may be acute for rapidly dividing tissues (such as inflammation of the inside of the mouth) or delayed (such as necrosis of bones or nerves). Acute side effects develop during the treatment course and generally resolve within a couple of weeks, whereas delayed side effects may take months to years to develop. After treatment the area of skin around the tumor may become red or sore looking. Your veterinarian will prescribe tablets if they are concerned about your pet, but if you are worried make sure you voice your concerns at your next visit. Long-term problems are usually changes at the site of the treatment such as bald patches or white hair regrowing (where it should be colored).

If your cat has had an anesthetic, they should be fully recovered by the time you get home. Offer a light meal at teatime but do not be alarmed if your cat does not want to eat until the following day. Often a course of radiotherapy is given after a cancer has been removed; if your cat has stitches keep a close eye on these as the radiation treatment may delay healing.

If your cat is receiving medication for other conditions check with your veterinarian that you should continue these throughout the radiotherapy course.