Since ionising radiation always has clinical consequences for a patient no matter how small the quantity, one must be careful in its use for diagnosis and treatment; always ensure there is a net benefit to the patient whenever it is used. As such, there are tight legal frameworks for ensuring ionising radiation is used wisely and that the risks of its use are suitably understood. In general terms, this means that keeping all doses As Low as Reasonably Achievable (ALARA) or Practicable (ALARP) are highly important considerations and are the basis of international guidance governing the use of radiation and protection from its use; e.g. through the International Commission on Radiological Protection (ICRP). Each country has its own legal framework within which the safe use of ionising radiation is governed, particularly for medical exposure. In the UK, this comes under the Ionising Radiations (Medical Exposure) Legislation 2017 (IRMER 2017), the legislation that governs both diagnostic and therapeutic use. Once the clinical team (in the UK, within the multidisciplinary team, or MDT) has decided to treat a patient with radiotherapy, one must be aware of all the exposures of radiation needed to plan and verify the treatment course; this can be numerous in a radiotherapy clinical pathway. In this chapter, we discuss the types of radiation exposure anticipated, which are not part of the treatment itself, the principles involved in minimising such doses, and the legal frameworks that operate to ensure these aspects that protect the patient.