The development of a new basic treatment equivalent model to assess linear accelerator throughput.

ABSTRACT

AIMS: The basic treatment equivalent (BTE) model was developed in 1996 in an attempt to improve the measurement of linear accelerator throughput in radiotherapy. This study aimed to assess the effect of treatment set-up and patient characteristics on fraction duration, to update the BTE model and to determine the better throughput measure between fields per hour and BTE per hour. MATERIALS AND METHODS: Stopwatch measurements of the duration of each radiotherapy treatment fraction delivered on each linear accelerator in participating New South Wales radiation oncology departments over a 5-day period in 2003 were undertaken. Patient, equipment and staff data were collected to assess the effect of these variables on fraction duration. A new BTE equation was derived, including the most significant variables. Statistical comparison of fields and BTE per unit time was made to assess the better predictor of fraction duration. RESULTS: Data collected on 27 linear accelerators in 13 departments included a total of 135 days of linear accelerator operation, 4316 fractions and 12 892 treatment fields. Seventeen factors significantly influenced fraction duration (P < 0.01). These accounted for 46% of the total variance in the models. The eight most influential predictors of prolonged fraction duration were included in the BTE model. These were as follows high number of fields, high number of port films/electronic portal imaging, absence of automatic field-sequencing and multi-leaf collimation, high number of junctions, use of bolus and first fraction of a treatment course. The BTE per hour was shown to be a better predictor of throughput than fields per hour. CONCLUSIONS: The BTE model is a better measure of linear accelerator throughput. It incorporates weightings for treatment and patient factors that significantly influenced fraction duration. This measure could be routinely collected by the radiation oncology departments and included in the electronic radiotherapy information systems.