Quality assurance in preoperative radiotherapy of rectal cancer: evaluation of a pre-trial dummy-run

Purpose: To assess inter-institution variability of treated volumes in preo perative radiotherapy for rectal cancer among Austrian radiotherapy institu tions in the framework of a multi-centre phase-In clinical trial. Materials and,methods: All eleven Austrian radiotherapy departments were in vited to participate in this pre-study dummy-run. They received a short his tory of two 'dummy patients' (case A and case B); three computer assisted t omography (CT) slices. simulation films; and the protocol describing the ra diation technique to be used. Participants were asked to prepare a treatmen t plan for tither case on the basis of the materials provided and to use th eir computerized planning systems. Additionally and independently of the CT -based treatment plans. they were asked to delineate the fields to be treat ed on the simulation films. Results: Nine of eleven departments participated. All participants used a t hree or four field technique as requested. The variation of beam widths and planning target volumes (PPVs) in the central plane was 6-11% and 11-16%, respectively. The standard deviations (SD) were 21 and 24% for the two case s for mean treated volumes of 2.1 and 2.91, respectively. The variation of beam widths in the central plane was less pronounced in the simulation base d treatment plans as compared with the CT-based treatment plans for the dor sal fields: the opposite was true for the laterals. Conclusion: Considerable variation of treated volumes is inevitable in mult i-institution trials despite detailed treatment guidelines Simulator based treatment fields seem to result in less pronounced inter-institution variat ions compared with CT-based treatment planning, if bony landmarks can be us ed as is the case in rectal cancer. Continuous quality control is thus wan- anted in multi-centre trials to increase homogeneity of volumes treated. (C ) 2000 Elsevier Science Ireland Ltd. All rights reserved.