“…Much of the recent work on outlining variation in the UK has been conducted within the Radiotherapy Trials Quality Assurance (RTTQA) group. Outlining for clinical trials is assessed both in the clinician pre-trial approval for participation in a specific trial or group of trials [4] and in individual case reviews of on-trial patients [10]. The pre-accrual outlining exercise is commonly compared with a predefined reference (gold standard) volume, which may be defined by an individual clinician, but more commonly by a group of senior clinical oncologists, as this reflects the uncertainties and variations that occur even among expert outliners [11].…”