An End-to-End Assessment of Localization and Dosimetric Accuracy for the LAP Luna 3D Sgrt System
Abstract
Purpose
To quantify the geometric localization and dosimetric accuracy of a novel 3D surface-guided radiotherapy (SGRT) system (LAP LUNA) using an end-to-end anthropomorphic phantom test.
Methods
An anthropomorphic end-to-end phantom (CIRS Model 036A) was imaged, with an Exradin A16 ion chamber inserted at the target isocenter. A single-fraction 5 Gy VMAT plan was generated using the Eclipse TPS. The DICOM dataset was exported to the SGRT system. The phantom was first positioned using only LAP LUNA SGRT guidance, and the residual real-time deltas were recorded. The plan was delivered, and the absolute dose was measured. Subsequently, a CBCT was acquired to determine setup corrections based on internal anatomy. These image-guided corrections were recorded, the phantom position was adjusted, and the plan was re-delivered to establish a baseline dosimetric measurement.
Results
The residual setup errors identified by CBCT after initial SGRT alignment were ≤1 mm in all translational axes (VRT, LNG, LAT) and ≤0.1° in all rotational axes (RTN, PITCH, ROLL). The dose measured following SGRT-only setup was within 0.05% of the dose measured with the CBCT-corrected setup. The absolute dose measured with the SGRT setup was -3.32% compared to the TPS-planned dose.
Conclusion
This end-to-end assessment demonstrates the LAP LUNA 3D SGRT system achieves a high degree of geometric localization accuracy, with translational and rotational deviations within 1 mm and 0.1°, respectively. The resulting dosimetric agreement was negligible (<0.1%) when compared to a CBCT-based setup, indicating high confidence in SGRT as a primary positioning modality. The observed geometric accuracy meets the ≤1 mm tolerance for SRS/SBRT recommended by AAPM TG-302. Furthermore, the overall end-to-end dosimetric accuracy of -3.32% (measured vs. plan) is well within the ≤5% tolerance recommended by AAPM MPPG 5.a for complex IMRT/VMAT delivery, validating the entire treatment chain.