Room: Exhibit Hall | Forum 7
Purpose: To determine optimal dose distribution in the treatment planning of volumetric modulated arc therapy (VMAT), a virtually perfect dose distribution calculator was developed as a reference of optimization by applying CT reconstruction like filtered back projection process.
Methods: Delineated structures on patient CT were exported from treatment planning system in DICOM format. The patient body and planning target volume (PTV) were placed on 3-D voxel space. The sinogram of PTV was calculated by its projection along X-ray direction for each rotational angle. Each projection was Fourier transformed to frequency space, applied the Shepp-Logan filter, then back to real space by inverse Fourier transformation. Since dose irradiation cannot take a negative value, filtered projections lifted up using the minimum values on inside of PTV. All values on the outside of PTV set to zero. Unlike CT image reconstruction, X-ray attenuates inside of body. Corrected projections, which applied the percent depth dose according to each voxel depth from body surface, were placed back on the 3-D voxel space along X-ray direction. Finally, dose distributions of multiple rotational angle were convoluted. Dose volume histogram (DVH) was generated from this convoluted dose distribution.
Results: The original application for geometrically ideal dose simulator was successfully developed. We confirmed the efficacy of it to determine excessive/insufficient inputs of optimization parameters by comparing DVHs between the ideal dose calculation and clinical used VMAT planning.
Conclusion: By employed CT reconstruction like techniques, the ideal dose distribution, which included some of characteristics of photon interaction while excluded device oriented limitation, could be generated. Since current planning workflow cannot establish the mathematically perfect solution, planners need to consider a good balance between covering PTV and sparing normal tissue rely on their experience. Our application will strongly support on determination of VMAT planning optimization by providing the reference dose distribution.