The future of radiotherapy in small animals - should the fractions be coarse or fine?

Radiation therapy has been used to treat animal cancers for more than 100 years. Clinical experiences and experimental results have been widely published and provide a basis for the recognition of radiation therapy as an integral component of multimodal cancer management in veterinary oncology. As the expectations of pet owners and the demand for treatment of companion animals with cancer have increased, veterinary oncology itself has undergone dramatic advances in the past several decades both in terms of improved diagnostics and treatments, including increased accessibility of radiation therapy. Synchronous with development of the specialism of veterinary radiation oncology, confusion and controversy have arisen with regard to distinguishing between different types of radiotherapy and methods of treatment delivery. Importantly, the confusion extends beyond semantics, and includes opinionated debate about defining which forms of therapy (if any at all) are optimal for a given patient. This exemplifies how, despite marks of maturity including age and a robust publication history, the field of veterinary radiation oncology is in some ways still in its infancy. The purpose of this article is to review the evidence base for daily (fine) fractionation versus weekly (coarse) hypofractionation in veterinary oncology, using selected tumour types as examples.