Comprehensive performance evaluation of single-isocenter multi-target treatment plans using a 3D-printed phantom and a Python Winston-Lutz test module

Abstract

The conventional Winston--Lutz (WL) test verifies coincidence between the mechanical and radiation isocenters of a linear accelerator (LINAC), but its standard implementation is limited to a single target at isocenter. For single-isocenter multi-target (SIMT) treatments, off-axis targets require additional geometric verification. This study evaluated a low-cost 3D-printed phantom for SIMT verification using a modified open-source multi-target WL workflow. The phantom was fabricated from eSUN PLA+ using a Bambu Lab P1P printer and embedded with five 5 mm tungsten carbide ball bearings (BBs). Ten gantry-collimator-couch combinations were delivered on a Varian Clinac CX using a 6 MV beam, and EPID DICOM images were analyzed with a modified Pylinac module. Across three trials, all BB localization deviations remained below the 2 mm tolerance applied to this IMRT-capable system, with an observed range of 0.16–1.94 mm. The results support additive manufacturing and open-source analysis as an accessible SIMT QA development approach, while further validation is required before certified clinical replacement.