First experiences in using a dose control system on a TomoTherapy Hi·Art II

The purpose of this study was to investigate the impact of a dose control system (DCS) servo installed on two fully commissioned TomoTherapy Hi·Art II treatment units. This servo is designed to actively adjust machine parameters to control the output variation of a tomotherapy unit to within ± 0.5% of the nominal dose rate. Machine output, dose rate, and patient-specific quality assurance data were retrospectively analyzed for periods prior to and following the installation of the servo system. Quality assurance tests indicate a reduction in the rotational variation of the output during a procedure, where the peak-to-peak amplitude of the variation was ± 1.30 prior to DCS and equal to ± 0.4 with DCS. Comparing two tomotherapy unit static outputs over four years the percentage error was 1.05% ± 0.7% and -0.4% ± 0.66% and, once DCS was installed, was reduced to -0.22% ± 0.29% and -0.08% ± 0.16%. The results of the quality assurance tests indicate that the dose control system reduced the output variation of each machine for both static and rotational delivery, leading to an improvement in the overall performance of the machine and providing greater certainty in treatment delivery.