TABLE III.

Descriptions of the analysis methods used to help identify the errors.

Method	Description
Ion chamber	Measure absolute dose in region of interest with micro-chamber (if possible). This method is useful if there is a large enough region of consistent and unidirectional dose bias
Dose profiles	Plot absolute dose profiles, planned vs measured, through region(s) of interest
2%L/2 mm error pattern	Employ a sensitive metric and examine patterns of error in the dose distribution
EPID-based	Use EPID input to predict high-density dose planes for more thorough analysis than sparse arrays. The specific tool used in this study was EPIDose. This implementation of EPID-based dosimetry reconstructs planar dose in a phantom for comparison with TPS-calculated dose, as opposed to comparing EPID images generated by a separate algorithm, which does not audit the TPS dose calculation (Ref. 25)
3D measurement guided dose reconstruction (MGDR)	Use measurement-guided dose reconstruction technique to use QA measurements to estimate 3D dose with the TPS voxel resolution, either on a phantom dose or on the patient CT dataset. The specific tool used in this study was 3DVH
Dose grid inspection	Use graphical tools to inspect the TPS dose grid, including extents, resolution, and volume filled by nonzero dose voxels