Room: AAPM ePoster Library
Purpose: To introduce and evaluate a 3-dimensional (3D) film stack dosimeter formulated using leuco crystal violet (PRESAGE-LCV) and its application of dose verification for treatments involving complex dose distributions such as volumetric modulated arc therapy (VMAT).
Methods: Twenty-nine PRESAGE-LCV sheets with dimensions of 12 cm x 13 cm x 0.3 cm were used in the creation of a film stack with four nylon rods holding the stack together at the edge of each sheet. The PRESAGE-LCV stack was irradiated using a VMAT 6X treatment plan delivered using two arcs from a clinical linear accelerator. Following the stack’s irradiation, each sheet from the stack was scanned, with the netOD distribution image of each scanned sheet translated, rotated, and aligned after applying image registration. Image registration of each scanned sheet was guided by the holes in the corners of each sheet used for the insertion of the nylon rods holding the stack together. Using the registered netOD image of the sheets, the twenty-nine sheet images were imported into MATLAB as a 3D matrix with the measured pixel intensity values from each sheet normalized to the maximum value of the sheet at the isocenter. Comparison of the normalized measured dose distribution with the treatment planning system (TPS) was performed in the coronal, sagittal, and transverse orientations.
Results: At selected planes in the coronal, sagittal, and transverse orientations, the 2D gamma pass-rate exceeds 95% when using a criteria of 2%/2mm (10% threshold). 2D gamma tests were also performed at different depths (1.5 cm above and below the isocenter) in the coronal orientation of the film stack, all of which exceed a 90% pass-rate using a criteria of 3%/3mm.
Conclusion: The results from this study show that PRESAGE-LCV film-stack has the potential to provide a high resolution, accurate, three-dimensional tool for VMAT dose distribution verification.