Purpose: To quantify the effect of CT simulation reconstruction kernels on various dose calculation algorithms with heterogeneity correction
Methods: The Gammex Electron Density (ED) Phantom was initially scanned with the Siemens PET/CT Biograph20 mCT: 120kVp, 332mAs (CareDose4D on), 2mm slices, 0.8 pitch, 500mm FOV. The raw data was reconstructed with nine different kernel options in order to generate Hounsfield Unit (HU) versus ED curves and to compare absolute differences in HU. Repeat scans were then acquired under head and pelvis protocols: 120kVp, 100mAs, 2mm slices, pitch of 0.55/0.8, 500mm FOV; and reconstructed per H40s (head) and B40s (pelvis) kernels. Raw data from a full-body patient scan was also reconstructed using the B20, B40, B70, and B80 kernels. For each reconstruction, photon (3DCRT and VMAT), electron (en face 18 and 20MeV) and proton (single field) treatment plans were generated using Varian Eclipse dose calculation algorithms: AAA, Acuros, eMC, and PCS. Photon and electron plans were also simulated to pass through cortical bone versus liver plugs of the phantom for kernel comparison. Treatment field monitor units (MU) and isodose volumes were compared across all scenarios.
Results: The largest absolute difference in HU between the nine kernels was 48.2HU (6.1%) for bone CB2-50% material when comparing B40 versus H40 kernels. The largest difference between the â€˜Bâ€™ kernels was in Cortical Bone, 14.8 HU (1.2%). The largest difference between the â€˜Bâ€™ and â€˜Dâ€™ kernels was in Cortical Bone, 19.2 HU (1.6%). MU comparisons across all calculation algorithms for the patient and phantom scans were within 1-2MU. Maximum differences in isodose volumes (V105%, V100%, V90%) observed were 22.6cc (3.3%).
Conclusion: MU differences across the various kernel generated plans were minimal for photon, electron, and proton algorithms. The changes in isodose volumes due to the different kernels were also clinically insignificant across plans.