Cancer is an important cause of death in pets, representing 25% of dogs over 2 years old, and 45% over 10 years old (Villalobos 2011 a). Being a common disease in humans, most owners would have had personal experience of either a family member or friend that has been affected by cancer. It has been described as one of the main concerns in owner´s minds in respect of quality of life (QoL) and health of their pets (Withrow et al 2013). In veterinary oncology, treatments have evolved in parallel with human oncology. The goal of treatment in veterinary medicine tends to be QoL as well as tumour control or remission. Qo seems an important consideration in decision-making for owners with pets diagnosed with cancer (Moore 2011). Radiation therapy has been used since the beginning of 20th century in veterinary medicine (Whiteley and Kestenman 1991). It is an effective treatment option for many solid tumours in dogs. The last two decades has seen it become more available in the United Kingdom and several centres are offering it. It can be used for curative intent or palliatively (LaRue and Gordon 2013). External beam radiotherapy is used to treat types of tumours such as nasal carcinomas, sarcomas, brain tumours, oral tumours, thyroid and mediastinal neoplasia, spinal cord and many others (LaRue and Gordon 2013). Side effects of radiation therapy can be divided into acute (or early) and late side effects. Acute effects occur soon during or after radiation therapy. They involve rapidly dividing tissues as skin, mucosa, epithelial structures of the eye and intestine. Acute side effects can be unpleasant and distressing for some owners but usually resolve quickly and are self-limiting (LaRue and Gordon 2013).