Analysis of utilization-related parameters on a 6-MV linear accelerator.

An analysis of unscheduled downtime and of patient treatment data for a 6-MV linear accelerator is presented for a 7-yr period. Following the initial year of clinical use, the unscheduled downtime has averaged 2.4%, with a corresponding loss of 1.3% in patient treatments. The quality assurance, preventive maintenance, and repairs are handled in-house, with an investment of approximately 500 man-hours annually.

A statistical analysis of ionometrically measured 6-MV x-ray beam parameters.

A statistical analysis has been made of ionometrically measured parameters related to the central-axis output, the beam symmetry, the beam flatness, and the depth dose for the 6-MV x-ray beam from the Therac-6 linear accelerator. The means and coefficients of variation of the measurements are determined on a monthly basis for each parameter. Mean coefficients of variation less than +/- 1% have been determined and are useful in establishing the optimal limits of acceptance of these parameters. The results of this study indicate that the long-term stability of the radiation parameters associated with this unit can be maintained within acceptable limits with a consistent quality-assurance program.