PURPOSE
Helical tomotherapy has been in clinical use for several years. One of the issues with a helical tomotherapy unit is the failure of detection of the x-ray target. In this study, we are proposing a method to detect potential failure of the x-ray target.
METHODS
Currently, on-board detector data from a helical tomotherapy unit are collected and sent to TomoTherapy Inc. for comparison with the so-called gold standard for the unit. However, this is sometimes time-consuming. Furthermore, the clinical medical physicists have no access to this comparison procedure. In this study, we developed a practical method to detect target failure based on one of the monthly quality assurance (QA) procedures. The commissioning cross-plane profiles were used as the comparison baseline. Larger EDR2 film (35×43 cm) were set at source-axis distance (SAD) (85 cm) and shot with 1.5 cm solid water as build-up material and 10 cm solid water as backscattering material. Cross-plane profiles obtained from the EDR2 film were compared with the commissioning profiles.
RESULTS
When the cross-plane profiles from monthly QA have 1° degree difference from the commissioning profiles, it is time that the target be changed.
CONCLUSION
This method enables the clinical medical physicists to easily evaluate the target status and to help improving the quality assurance of a helical tomotherapy unit.