Quality assurance in the CHART clinical trial.

As part of the clinical trial of CHART (continuous hyperfractionated accelerated radiotherapy) a quality assurance programme was included. The technical part of this--which is reported in this paper--is a series of tests designed to check all aspects of treatment planning and delivery. The results of visits to the 13 participating centres--and repeat visits to some of these centres--are discussed. The main areas tested were as follows. The linear accelerator: mechanical, and optical, scales and indicators; radiation field size; flatness and symmetry. DOSIMETRY: output; wedge factor; beam energy; phantom measurements against a plan calculated by the centre. SIMULATOR: mechanical, optical scales and indicators. The results show these centres work within the tolerances chosen for most parameters. Flatness, wedge factor and energy were areas of weakness in some centres. This must be partly the cause of the spread of phantom measurements which, after removal of variations in output, still range from -7 to +6% between calculated and measured values.