Can a commercially available EPID dosimetry system detect small daily patient setup errors for cranial IMRT/SRS?

Publication date: Available online 24 December 2016
Source:Practical Radiation Oncology
Author(s): Emmelyn S. Hsieh, Katherine S. Hansen, Michael S. Kent, Sanjeev Saini, Sonja Dieterich
PurposeThe purpose of this study was to determine if the Sun Nuclear PerFRACTION EPID dosimetry software would be able to detect setup errors in a clinical setting and would be able to correctly identify in which direction the setup error was introduced.Methods and MaterialsA 7-field IMRT treatment plan for a centrally located tumor was developed for one phantom and five canine cadaver heads. Systematic setup errors were introduced by manually moving the treatment couch by 1mm, 3mm, and 5mm in each translational direction to assess SRS, IMRT and 3D treatment tolerances after the initial alignment was performed. An angular setup error of 5 degrees yaw was also assessed. The delivered treatment fluence was automatically imported in the Perfraction software and compared to the baseline fluence.ResultsIn the canine phantom, a 5mm shift was undetected by gamma analysis, and up to a 2cm shift had to be introduced for the gamma pass rate of 3%/3mm to fall below a 95% pass rate criteria. The same 5mm shift using 3% percent difference caused the pass rates for two fields to drop below the 95% tolerance. For each respective translational shift, the affected beam angles were consistent across the cadaver heads and correlated with the direction of translational shift. The best field pass rate, worst field pass rate, and average pass rate across all seven fields was analyzed to develop clinical guidance on parameter settings for SRS, IMRT and 3D tolerances.ConclusionsPerFRACTION 2D mode successfully detected setup errors outside the systematic error tolerance for SRS, IMRT and 3D when an appropriate analysis metric and pass/fail criteria was implemented. Our data confirms that percent difference may be more sensitive in detecting plan failure than gamma analysis.



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