Objective Little is understood about the anxiety experienced by cancer patients undergoing radiotherapy or investigative imaging. Our aim was to identify sources of anxiety, the points along the cancer journey where anxiety occurred and methods to alleviate it. Methods Six focus groups were conducted with cancer patients (n = 17), caregivers (n = 3) and healthcare practitioners (HCPs; n = 10) in the radiotherapy department. Patients described specific elements in the care pathway which induced anxiety, while HCPs focused on their perception of the patient experience. Thematic analysis was used to analyse data. Results Three broad themes emerged: The Environment, The Individual and The Unknown. The physical environment of the hospital, inside the scanner for example, emerged as a key source of anxiety. The impact of cancer on patients' individual lives was significant, with many feeling isolated. The majority of participants described anxiety associated with the unknown. HCPs reported difficulty in identifying the anxious patient. Conclusions Anxiety is experienced throughout the cancer pathway. Common sources include the physical environment and the uncertainty associated with having cancer. Identifying both anxiety-inducing factors, and the anxious patients themselves, is crucial to enable targeted interventions to alleviate anxiety.