Radiotherapy

Radiotherapy (radiation therapy) is a form of treatment in which high-energy rays are used selectively to damage cancer cells or slow their growth. In dogs, it is primarily used when tumours are localised – either as sole therapy or in addition to surgery and chemotherapy. It is particularly useful for tumours that can hardly be completely removed surgically, whether due to their location or the risk of leaving tumour cells behind during the procedure.

When is radiotherapy used in dogs?

In veterinary medicine, radiotherapy is employed when a tumour is spatially limited but not easily operable. The most common diagnoses where this becomes relevant are:

1. Mast cell tumours: Among the most common types of cancer in dogs overall. Radiation is particularly considered when surgical removal was incomplete or the tumour is unfavourably located – for example on the head or a limb.
2. Soft tissue sarcomas: Malignant tumours in muscles or connective tissue. Here, irradiation often follows surgery to reach remaining cells that the scalpel could not remove.
3. Fibrosarcomas and osteosarcomas: Affect connective tissue or bone and are notoriously difficult to resect. Radiation can help alleviate pain and slow growth here – even if complete healing is not the goal.
4. Nasal tumours: Tumours in the nasal cavity are hardly accessible surgically. Therefore, radiotherapy is considered the preferred option for this location.
5. Brain tumours: Many brain tumours cannot be operated on or only at great risk. Radiation can help reduce tumour mass and slow progression.
6. Lymphomas: For certain localised or therapy-resistant lymph node tumours, radiotherapy is a supplementary or alternative method.

What should radiotherapy achieve?

The objectives depend heavily on the stage of the disease and which other treatments are running concurrently. Broadly speaking, three approaches can be distinguished:

1. Curative radiotherapy: Here, the stated goal is to completely destroy the tumour – particularly for small, clearly definable tumours with favourable initial conditions.
2. Adjuvant radiotherapy: Follows surgery and aims to eliminate residual cells that remain in the body. In other words, a follow-up treatment acting as a safety net.
3. Palliative radiotherapy: When a cure is no longer realistic, quality of life takes centre stage – alleviating pain, mitigating symptoms, and giving the dog weeks with fewer complaints.

How does radiotherapy work?

Radiotherapy cannot simply be carried out casually – it requires careful preparation so that the radiation hits the tumour as precisely as possible while sparing surrounding healthy tissue.

Preparation phase:

• Initial examination and diagnostics: First, the tumour is mapped in detail. This requires imaging techniques – X-rays, CT or MRI – to determine position, size and extent.
• Treatment planning: Based on these findings, the specialist team determines the necessary dose and from which angle the radiation is applied. This sounds technical – and it is. Errors in this phase directly affect efficacy and tolerability.

Treatment phase:

• Anaesthesia or sedation: The dog must remain absolutely still during irradiation. Therefore, it is sedated or briefly anaesthetised – which also means that each session entails requirements related to anaesthesia.
• The actual irradiation: The session itself lasts only a few minutes. High-energy radiation precisely hits the target area. Since a single high dose would do more harm than good, the total dose is usually distributed over several weeks – this maximises efficacy and reduces the risk of side effects.

Aftercare and monitoring:

• After each session, the dog remains under observation. The vet checks whether side effects occur or are indicated – and adjusts further proceedings accordingly if necessary.
• Regular check-ups are not a bureaucratic requirement but a genuine safety net: they show whether the therapy is taking effect and enable early counteraction in case of complications.

Side effects of radiotherapy

Radiotherapy is targeted – but it is not a laser that hits exclusively cancer cells. Healthy neighbouring tissue can also be affected. Side effects fall into two groups: those that occur during or shortly after treatment, and those that become visible only months or years later.

Acute side effects

They manifest during therapy or immediately afterwards and usually subside once treatment is completed.

Skin reactions:

• Redness, swelling and mild burns in the irradiated area are among the most common signs.
• The skin becomes more sensitive; in more pronounced cases, hair loss or dandruff may occur.

Inflammation in the irradiated area:

• Especially when mucous membranes are affected – for example in the oral cavity – swelling and inflammation can develop, which noticeably distress the dog.

Fatigue:

• Some dogs appear more lethargic than usual during the therapy phase. This is not imaginary: the body reacts to the strain caused by repeated anaesthesia and the radiation itself.

Loss of appetite and nausea:

• If tumours in the head, neck or digestive area are irradiated, the dog may temporarily eat less or show signs of nausea.

Late-onset side effects

These consequences sometimes develop only months or even years after completion of therapy – and are often permanent in nature.

Scarring and fibrosis:

• In the irradiated tissue, long-term hardening or fibrosis can occur, which may restrict mobility in the affected area.

Permanent hair loss:

• In some cases, the coat does not grow back in the irradiated area. This is cosmetic, but depending on the location, it can also have functional significance.

Damage to surrounding organs:

• If irradiation takes place near the brain or spinal cord, there is a risk of long-term damage to these sensitive structures – an aspect that specialised oncologists pay particular attention to during planning.

Secondary tumours:

• Very rare, but documented: In individual cases, radiation can favour the development of new tumours in the irradiated area. The risk is low, but should be addressed in the consultation.

What are the chances?

This depends – as is often the case in oncology – on several factors: type of tumour, location, stage, general condition of the dog and the timing of therapy initiation. As a rule:

• Curative radiotherapy can lead to long-term tumour control in many cases – under favourable conditions, sometimes even to complete healing.
• Palliative radiotherapy often improves quality of life noticeably: less pain, better general well-being – even if the tumour itself can no longer be completely eliminated.

Conclusion

Radiation therapy is not a panacea, but for many dogs with localised or inoperable tumours it is one of the most effective options that veterinary medicine offers today. Side effects can often be mitigated with good planning – many dogs tolerate the treatment surprisingly well. The crucial factor remains: the earlier the diagnosis is made and the better the therapy is tailored to the individual dog, the better the prognosis and quality of life.