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A practical method to detect target failure of a helical tomotherapy unit
S Stathakis1, A Gutierrez, C Esquivel
1Department of Radiation Oncology, University of Texas Health Science Center at San Antonio, San Antonio, TX 78229, USA. stathakis@uthscsa.edu
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.
