What is Radiotherapy?
Radiotherapy (RT) is the use of high-energy X-rays to kill cancer cells. These are usually produced by a large machine called a linear accelerator (see photograph) which produces a beam of X-rays which can be directed at a tumour.
Radiotherapy is typically used:
- After surgery, when all the visible cancer has been removed but microscopic cancer has been left behind at the surgical site and so there is a risk of tumour re-growth ( (e.g. mast cell tumours and soft tissue sarcomas)
- For treatment of melanoma in the mouth of dogs, in combination with surgery or as an alternative to surgery
- For palliation/slowing down the growth of tumours that are not surgically removable – or where surgery would carry a significant risk to the patient
- For pain relief in dogs with primary bone tumours (e.g. osteosarcoma) or tumours that have metastasised (spread to) areas of bone.
How is the Radiotherapy Given?
The required radiation dose is not given as one single treatment, as the normal tissues surrounding the tumour would not be able to tolerate this. Each treatment is given under a very short general anaesthetic. In radiotherapy each treatment is known as a ‘fraction’.
Definitive Treatment (Curative-Intent Treatment)
This is usually the protocol of choice for most cancers as it gives the best chance of long-term tumour control.
Treatment in the UK is usually given every Monday, Wednesday and Friday for our consecutive weeks – i.e. 12 treatments over four weeks. Patients may also have to attend the Radiotherapy centre for an initial session prior to treatment for an initial assessment (especially needed for tumours of the head and neck i.e. nasal cavity tumours, brain tumours, complex oral tumours or unusual thyroid tumours). In these cases a head/neck mould will be created at the same time to allow accurate patient placement, beam alignment and to immobilise the head during therapy (if required).
Radiotherapy will require careful planning from MRI/CT scans and utilises computerised planning to target the dose to the tumour whilst avoiding the surrounding normal brain and other important structures such as the eyes, ears and inside the mouth. However, it is inevitable that there will be some dose to these areas, as a margin has to be added to target microscopic tumour cells away from the main tumour and allow for subtle patient movement during treatment. Further scans/special computerised planning is not always required, particularly for the treatment of simple post-operative scars.
Twelve small fractions of radiation are given for brain tumours (as opposed to a smaller number of treatments, each at a higher dose) to limit both any acute side-effects (e.g. brain swelling in the case of brain tumours or nasal cancers) and also to minimise risks of late side-effects, such as long-term brain damage. Using this higher number of fractions of radiotherapy, Specialists can safely administer greater total doses of radiation, which improves the probability of controlling the tumour for longer. Slightly different protocols may be given by certain centres, either as their main protocol or as modifications for individual patients.
Palliative Treatment (Hypofractionated Treatment)
Treatment in the UK is usually given once a week for four consecutive weeks i.e. four treatments in total. In certain cases, such as oral malignant melanoma in dogs, this protocol is preferred. The advantages of hypofractionated treatment are that there are fewer treatments, it is cheaper and the dose is lower resulting in fewer side effects (e.g. sore skin/gums). However, as the dose is lower there is less chance of controlling the cancer and there is a higher risk of late side effects.
What are the Possible Side Effects of Radiotherapy?
The vast majority of dogs receiving this treatment enjoy an excellent quality of life and continue with their normal daily routine. Radiotherapy is a localised treatment, (i.e. directed to one small area of the body), and so the side effects are limited to the area being treated.
Acute Side Effects (whilst the patient is undergoing a course of treatment): These side effects are more likely to happen in the third and fourth week of therapy and can sometimes worsen for a week or two after treatment ceases. Side effects will depend on the area being treated and can include localised hair loss, sore skin, sore gums/lips, a sore eye(s) and some discomfort. Medications such as tablets or topical creams/eye drops are sometimes prescribed to manage these. They are temporary and disappear within a month of stopping treatment in most cases.
Serious Late Side Effects: These side effects are fortunately very rare and the risk is reduced by the small dose administered with each fraction in the case of definitive therapy. These can occur months or even years after radiation therapy and may include; skin changes, joint changes, cataracts and retinal changes, bone damage and very rarely even second unrelated cancers in the radiation treatment field. Fortunately the only common late side effects that we see are the hair growing back white in the treatment field and some thickening/changes to the skin.
What are the Most Common Causes of Faints or Fits?
The vast majority of dogs, tolerate the course of radiotherapy with few problems and owners are often very pleasantly surprised at how little the treatment has impacted on their quality of life/normal daily routine.
Treatment involves several anaesthetics, and so patients should be free of significant heart, kidney or liver disease and not experience concurrent problems that would be problematic.
Currently centres which offer radiation therapy:
- Southfields Veterinary Specialists
- University of Liverpool Veterinary School
- University of Cambridge Veterinary School
- University of Glasgow Veterinary School
- University of Edinburgh Veterinary School
- Animal Health Trust, Newmarket
Our Oncology Specialists work closely with the Specialists at the Radiation therapy Facilities to provide the best outcome for your pet.
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Find out more
To assist owners in understanding more about Cancer Care we have put together a range of information sheets to talk you through the some of the more common conditions seen and treated by our Specialists.