Purpose: To use Compass as a model-based quality assurance (QA) tool for stereotactic body radiation therapy(SBRT) and stereotactic radiation therapy (SRT) volumetric modulated arc therapy (VMAT) treatment plans calculated with Eclipse treatment planning system (TPS).

Materials and methods: Twenty clinical stereotactic VMAT SBRT and SRT treatment plans were blindly selected for evaluation. Those plans included four different treatment sites: prostate, brain, lung and body. The plans were evaluated against dose-volume histogram (DVH) parameters and 2D and 3D gamma analysis. The dose calculated with Eclipse treatment planning system (TPS) was compared to Compass calculated dose (CCD) and Compass reconstructed dose (CRD).

Results: The maximum differences in mean dose of planning target volume (PTV) were 2.7 ± 1.0% between
AAA and Acuros XB calculation algorithm TPS dose, −7.6 ± 3.5% between Eclipse TPS dose and CCD dose and −5.9 ± 3.7% between Eclipse TPS dose and CRD dose for both Eclipse calculation algorithms, respectively. 2D gamma analysis was not able to identify all the cases that 3D gamma analysis specified for further verification.

Conclusions: Compass is suitable for QA of SBRT and SRT treatment plans. However, the QA process should
include wide set of DVH-based dose parameters and 3D gamma analysis should be the preferred method when performing clinical patient QA. The results suggest that the Compass should not be used for smaller field sizes than 3×3 cm2 or the beam model should be adjusted separately for both small (FS≤3 cm) and large
(FS > 3 cm) field sizes.