On request, the IAEA performs comprehensive audits of radiotherapy programmes to assess the whole process, including aspects such as organization, infrastructure and clinical and medical physics components. The objective of a comprehensive clinical audit is to review and evaluate the quality of all components of the practice of radiotherapy at the institution, including its professional competence, with a view to quality improvement. A multidisciplinary team, known as Quality Assurance Team in Radiation Oncology (QUATRO), comprising a radiation oncologist, a medical physicist and a radiation therapist, are required to carry out the audit. The present publication provides revisions of the QUATRO guidelines published in 2007, by incorporating new procedures relevant to newer technologies and modalities that have become routinely used in radiotherapy centres in the interim period.