Background: Cone Beam Computed Tomography (CBCT), the focus of a number of radiotherapy fundraising campaigns in the mid-2000s, was introduced accompanied by a fanfare of newness and discourses of ‘hope’, ‘inspiring clinical confidence’ and ‘accuracy’. The CBCT system, used in the delivery of Radiotherapy treatment, was incorporated into strategic planning priorities across the United Kingdom based on a rationale of self-evidence. During this time, the way in which the new system was discussed with patients was variable. Research objectives: The purpose (...) of this study was to uncover how experimental practices were embedded and enacted during the use of a new technological system, specifically relating to how patients were enrolled during introductory phases of technology adoption. Research design and context: Drawing on ethnographic work and interviews with staff members in one hospital, the study examines staff discussions prior to the introduction of the Cone-Beam CT imaging system in radiotherapy. It considers how staff views were at odds with practices that occurred during the ‘experimental’ stages of use and how these were shared with patients. Ethical considerations: Approval was obtained from the Local National Health Service Research Ethics Committee and National Health Service Main Research Ethics Committee (REC 07/Q1308/16) for the interview and ethnographic stages, respectively. All names have been changed and participants signed a consent form. Findings: Staff reported a lack of evidence, absence of proof and perturbing doubts with the X-ray volumetric imaging. Both patients’ and practitioners’ partial understanding about the risks and benefits of the system created incommensurable ideas regarding its use and what the patients’ role was during these introductory stages. Conclusion: Maintaining partial truth telling renders patients’ experiences of new treatment at odds with ‘experimental’ practice. This has wide-reaching implications for practice. (shrink)